Concepts¶
The Airflow platform is a tool for describing, executing, and monitoring workflows.
Basic Airflow architecture¶
Primarily intended for development use, the basic Airflow architecture with the Local and Sequential executors is an excellent starting point for understanding the architecture of Apache Airflow.
There are a few components to note:
Metadata Database: Airflow uses a SQL database to store metadata about the data pipelines being run. In the diagram above, this is represented as Postgres which is extremely popular with Airflow. Alternate databases supported with Airflow include MySQL.
Web Server and Scheduler: The Airflow web server and Scheduler are separate processes run (in this case) on the local machine and interact with the database mentioned above.
The Executor is shown separately above, since it is commonly discussed within Airflow and in the documentation, but in reality it is NOT a separate process, but run within the Scheduler.
The Worker(s) are separate processes which also interact with the other components of the Airflow architecture and the metadata repository.
airflow.cfg
is the Airflow configuration file which is accessed by the Web Server, Scheduler, and Workers.DAGs refers to the DAG files containing Python code, representing the data pipelines to be run by Airflow. The location of these files is specified in the Airflow configuration file, but they need to be accessible by the Web Server, Scheduler, and Workers.
Core Ideas¶
DAGs¶
In Airflow, a DAG
-- or a Directed Acyclic Graph -- is a collection of all
the tasks you want to run, organized in a way that reflects their relationships
and dependencies.
A DAG is defined in a Python script, which represents the DAGs structure (tasks and their dependencies) as code.
For example, a simple DAG could consist of three tasks: A, B, and C. It could say that A has to run successfully before B can run, but C can run anytime. It could say that task A times out after 5 minutes, and B can be restarted up to 5 times in case it fails. It might also say that the workflow will run every night at 10pm, but should not start until a certain date.
In this way, a DAG describes how you want to carry out your workflow; but notice that we haven't said anything about what we actually want to do! A, B, and C could be anything. Maybe A prepares data for B to analyze while C sends an email. Or perhaps A monitors your location so B can open your garage door while C turns on your house lights. The important thing is that the DAG isn't concerned with what its constituent tasks do; its job is to make sure that whatever they do happens at the right time, or in the right order, or with the right handling of any unexpected issues.
DAGs are defined in standard Python files that are placed in Airflow's
DAG_FOLDER
. Airflow will execute the code in each file to dynamically build
the DAG
objects. You can have as many DAGs as you want, each describing an
arbitrary number of tasks. In general, each one should correspond to a single
logical workflow.
Note
When searching for DAGs, Airflow only considers Python files
that contain the strings "airflow" and "dag" by default (case-insensitive).
To consider all Python files instead, disable the DAG_DISCOVERY_SAFE_MODE
configuration flag.
Scope¶
Airflow will load any DAG
object it can import from a DAG file. Critically,
that means the DAG must appear in globals()
. Consider the following two
DAGs. Only dag_1
will be loaded; the other one only appears in a local
scope.
dag_1 = DAG('this_dag_will_be_discovered')
def my_function():
dag_2 = DAG('but_this_dag_will_not')
my_function()
Sometimes this can be put to good use. For example, a common pattern with
SubDagOperator
is to define the subdag inside a function so that Airflow
doesn't try to load it as a standalone DAG.
Default Arguments¶
If a dictionary of default_args
is passed to a DAG, it will apply them to
any of its operators. This makes it easy to apply a common parameter to many operators without having to type it many times.
default_args = {
'start_date': datetime(2016, 1, 1),
'owner': 'airflow'
}
dag = DAG('my_dag', default_args=default_args)
op = DummyOperator(task_id='dummy', dag=dag)
print(op.owner) # airflow
Context Manager¶
Added in Airflow 1.8
DAGs can be used as context managers to automatically assign new operators to that DAG.
with DAG('my_dag', start_date=datetime(2016, 1, 1)) as dag:
op = DummyOperator('op')
op.dag is dag # True
TaskFlow API¶
New in version 2.0.0.
Airflow 2.0 adds a new style of authoring dags called the TaskFlow API which removes a lot of the boilerplate around creating PythonOperators, managing dependencies between task and accessing XCom values (During development this feature was called "Functional DAGs", so if you see or hear any references to that, it's the same thing).
Outputs and inputs are sent between tasks using XCom values. In addition, you can wrap functions as tasks using the task decorator. Airflow will also automatically add dependencies between tasks to ensure that XCom messages are available when operators are executed.
Example DAG built with the TaskFlow API
with DAG(
'send_server_ip', default_args=default_args, schedule_interval=None
) as dag:
# Using default connection as it's set to httpbin.org by default
get_ip = SimpleHttpOperator(
task_id='get_ip', endpoint='get', method='GET', xcom_push=True
)
@dag.task(multiple_outputs=True)
def prepare_email(raw_json: str) -> Dict[str, str]:
external_ip = json.loads(raw_json)['origin']
return {
'subject':f'Server connected from {external_ip}',
'body': f'Seems like today your server executing Airflow is connected from the external IP {external_ip}<br>'
}
email_info = prepare_email(get_ip.output)
send_email = EmailOperator(
task_id='send_email',
to='example@example.com',
subject=email_info['subject'],
html_content=email_info['body']
)
DAG decorator¶
New in version 2.0.0.
In addition to creating DAGs using context manager, in Airflow 2.0 you can also
create DAGs from a function. DAG decorator creates a DAG generator function. Any function decorated with @dag
returns a DAG object.
DAG decorator also sets up the parameters you have in the function as DAG params. This allows you to parameterize your DAGs and set the parameters when triggering the DAG manually. See Passing Parameters when triggering dags to learn how to pass parameters when triggering DAGs.
You can also use the parameters on jinja templates by using the {{context.params}}
dictionary.
Example DAG with decorator:
@dag(default_args=DEFAULT_ARGS, schedule_interval=None, start_date=days_ago(2), tags=['example'])
def example_dag_decorator(email: str = 'example@example.com'):
"""
DAG to send server IP to email.
:param email: Email to send IP to. Defaults to example@example.com.
:type email: str
"""
get_ip = GetRequestOperator(task_id='get_ip', url="http://httpbin.org/get")
@task(multiple_outputs=True)
def prepare_email(raw_json: Dict[str, Any]) -> Dict[str, str]:
external_ip = raw_json['origin']
return {
'subject': f'Server connected from {external_ip}',
'body': f'Seems like today your server executing Airflow is connected from IP {external_ip}<br>',
}
email_info = prepare_email(get_ip.output)
EmailOperator(
task_id='send_email', to=email, subject=email_info['subject'], html_content=email_info['body']
)
dag = example_dag_decorator()
Note
Note that Airflow will only load DAGs that appear in globals()
as noted in scope section.
This means you need to make sure to have a variable for your returned DAG in the module scope.
Otherwise Airflow won't detect your decorated DAG.
executor_config
¶
The executor_config
is an argument placed into operators that allow Airflow users to override tasks
before launch. Currently this is primarily used by the KubernetesExecutor
, but will soon be available
for other overrides.
DAG Runs¶
A DAG run is an instantiation of a DAG, containing task instances that run for a specific execution_date
.
A DAG run is usually created by the Airflow scheduler, but can also be created by an external trigger.
Multiple DAG runs may be running at once for a particular DAG, each of them having a different execution_date
.
For example, we might currently have two DAG runs that are in progress for 2016-01-01 and 2016-01-02 respectively.
execution_date¶
The execution_date
is the logical date and time which the DAG Run, and its task instances, are running for.
This allows task instances to process data for the desired logical date & time. While a task instance or DAG run might have an actual start date of now, their logical date might be 3 months ago because we are busy reloading something.
In the prior example the execution_date
was 2016-01-01 for the first DAG Run and 2016-01-02 for the second.
A DAG run and all task instances created within it are instanced with the same execution_date
, so
that logically you can think of a DAG run as simulating the DAG running all of its tasks at some
previous date & time specified by the execution_date
.
Tasks¶
A Task defines a unit of work within a DAG; it is represented as a node in the DAG graph, and it is written in Python.
Each task is an implementation of an Operator, for example a PythonOperator
to execute some Python code,
or a BashOperator
to run a Bash command.
The task implements an operator by defining specific values for that operator,
such as a Python callable in the case of PythonOperator
or a Bash command in the case of BashOperator
.
Relations between Tasks¶
Consider the following DAG with two tasks. Each task is a node in our DAG, and there is a dependency from task_1 to task_2:
with DAG('my_dag', start_date=datetime(2016, 1, 1)) as dag:
task_1 = DummyOperator('task_1')
task_2 = DummyOperator('task_2')
task_1 >> task_2 # Define dependencies
We can say that task_1 is upstream of task_2, and conversely task_2 is downstream of task_1. When a DAG Run is created, task_1 will start running and task_2 waits for task_1 to complete successfully before it may start.
Python task decorator¶
New in version 2.0.0.
Airflow task
decorator converts any Python function to an Airflow operator.
The decorated function can be called once to set the arguments and key arguments for operator execution.
with DAG('my_dag', start_date=datetime(2020, 5, 15)) as dag:
@dag.task
def hello_world():
print('hello world!')
# Also...
from airflow.decorators import task
@task
def hello_name(name: str):
print(f'hello {name}!')
hello_name('Airflow users')
Task decorator captures returned values and sends them to the XCom backend. By default,
the returned value is saved as a single XCom value. You can set multiple_outputs
key argument to True
to unroll dictionaries, lists or tuples into separate XCom values. This can be used with regular operators to
create DAGs with Task Flow API.
Calling a decorated function returns an XComArg
instance. You can use it to set templated fields on downstream
operators.
You can call a decorated function more than once in a DAG. The decorated function will automatically generate
a unique task_id
for each generated operator.
with DAG('my_dag', start_date=datetime(2020, 5, 15)) as dag:
@dag.task
def update_user(user_id: int):
...
# Avoid generating this list dynamically to keep DAG topology stable between DAG runs
for user_id in user_ids:
update_user(user_id)
# This will generate an operator for each user_id
Task ids are generated by appending a number at the end of the original task id. For the above example, the DAG will have
the following task ids: [update_user, update_user__1, update_user__2, ... update_user__n]
.
Due to dynamic nature of the ids generations users should be aware that changing a DAG by adding or removing additional
invocations of task-decorated function may change task_id
of other task of the same type within a single DAG.
For example, if there are many task-decorated tasks without explicitly given task_id. Their task_id
will be
generated sequentially: task__1
, task__2
, task__3
, etc. After the DAG goes into production, one day
someone inserts a new task before task__2
. The task_id
after that will all be shifted forward by one place.
This is going to produce task__1
, task__2
, task__3
, task__4
. But at this point the task__3
is
no longer the same task__3
as before. This may create confusion when analyzing history logs / DagRuns of a DAG
that changed over time.
Accessing current context¶
To retrieve current execution context you can use get_current_context
method. In this way
you can gain access to context dictionary from within your operators. This is especially helpful when
using @task
decorator.
from airflow.decorators import task
from airflow.operators.python import get_current_context
@task
def my_task():
context = get_current_context()
ti = context["ti"]
Current context is accessible only during the task execution. The context is not accessible during
pre_execute
or post_execute
. Calling this method outside execution context will raise an error.
Task Instances¶
A task instance represents a specific run of a task and is characterized as the
combination of a DAG, a task, and a point in time (execution_date
). Task instances
also have an indicative state, which could be "running", "success", "failed", "skipped", "up
for retry", etc.
Tasks are defined in DAGs, and both are written in Python code to define what you want to do.
Task Instances belong to DAG Runs, have an associated execution_date
, and are instantiated, runnable entities.
Relations between Task Instances¶
Again consider the following tasks, defined for some DAG:
with DAG('my_dag', start_date=datetime(2016, 1, 1)) as dag:
task_1 = DummyOperator('task_1')
task_2 = DummyOperator('task_2')
task_1 >> task_2 # Define dependencies
When we enable this DAG, the scheduler creates several DAG Runs - one with execution_date
of 2016-01-01,
one with execution_date
of 2016-01-02, and so on up to the current date.
Each DAG Run will contain a task_1 Task Instance and a task_2 Task instance. Both Task Instances will
have execution_date
equal to the DAG Run's execution_date
, and each task_2 will be downstream of
(depends on) its task_1.
We can also say that task_1 for 2016-01-01 is the previous task instance of the task_1 for 2016-01-02.
Or that the DAG Run for 2016-01-01 is the previous DAG Run to the DAG Run of 2016-01-02.
Here, previous refers to the logical past/prior execution_date
, that runs independently of other runs,
and upstream refers to a dependency within the same run and having the same execution_date
.
Note
The Airflow documentation sometimes refers to previous instead of upstream in places, and vice-versa. If you find any occurrences of this, please help us improve by contributing some corrections!
Task Lifecycle¶
A task goes through various stages from start to completion. In the Airflow UI (graph and tree views), these stages are displayed by a color representing each stage:
The complete lifecycle of the task looks like this:
The happy flow consists of the following stages:
No status (scheduler created empty task instance)
Scheduled (scheduler determined task instance needs to run)
Queued (scheduler sent task to executor to run on the queue)
Running (worker picked up a task and is now running it)
Success (task completed)
Operators¶
While DAGs describe how to run a workflow, Operators
determine what
actually gets done by a task.
An operator describes a single task in a workflow. Operators are usually (but not always) atomic, meaning they can stand on their own and don't need to share resources with any other operators. The DAG will make sure that operators run in the correct order; other than those dependencies, operators generally run independently. In fact, they may run on two completely different machines.
This is a subtle but very important point: in general, if two operators need to share information, like a filename or small amount of data, you should consider combining them into a single operator. If it absolutely can't be avoided, Airflow does have a feature for operator cross-communication called XCom that is described in the section XComs.
Airflow provides many built-in operators for many common tasks, including:
BashOperator
- executes a bash commandPythonOperator
- calls an arbitrary Python functionEmailOperator
- sends an email
There are also other, commonly used operators that are installed together with airflow automatically, by pre-installing some Provider packages packages (they are always available no matter which extras you chose when installing Apache Airflow):
SimpleHttpOperator
- sends an HTTP requestSqliteOperator
- SQLite DB operator
In addition to these basic building blocks, there are many more specific operators developed by the
community that you can install additionally by installing community-maintained provider packages. You
can install them by adding an extra (for example ([mysql]
) when installing Airflow or by installing
additional packages manually (for example apache-airflow-providers-mysql
package).
Some examples of popular operators are:
But there are many, many more - you can see the list of those by following the providers documentation at Provider packages.
Operators are only loaded by Airflow if they are assigned to a DAG.
Sensors¶
Sensor
is an Operator that waits (polls) for a certain time, file, database row, S3 key, another DAG/task, etc...
There are currently 3 different modes for how a sensor operates:
Schedule Mode |
Description |
Use case |
---|---|---|
|
The sensor is taking up a worker slot for its whole execution time and sleeps between pokes. |
Use this mode if the expected runtime of the sensor is short or if a short poke interval is required. Note that the sensor will hold onto a worker slot and a pool slot for the duration of the sensor's runtime in this mode. |
|
The sensor task frees the worker slot when the criteria is not yet met and it's rescheduled at a later time. |
Use this mode if the time before the criteria is met is expected to be quite long. The poke interval should be more than one minute to prevent too much load on the scheduler. |
|
smart sensor is a service (run by a builtin DAG) which consolidate the execution of sensors in batches.
Instead of holding a long running process for each sensor and poking periodically, a sensor will only
store poke context at |
Use this mode if you have a large amount of sensor tasks running in your airflow cluster. This can largely reduce airflow’s infrastructure cost and improve cluster stability - reduce meta database load. |
How to use:
For poke|reschedule
mode, you can configure them at the task level by supplying the mode
parameter,
i.e. S3KeySensor(task_id='check-bucket', mode='reschedule', ...)
.
For smart sensor
, you need to configure it in airflow.cfg
, for example:
[smart_sensor]
use_smart_sensor = true
shard_code_upper_limit = 10000
# Users can change the following config based on their requirements
shards = 5
sensors_enabled = NamedHivePartitionSensor, MetastorePartitionSensor
For more information on how to configure smart sensor
and its architecture, see:
Smart Sensor Architecture and Configuration
DAG Assignment¶
Added in Airflow 1.8
Operators do not have to be assigned to DAGs immediately (previously dag
was
a required argument). However, once an operator is assigned to a DAG, it can not
be transferred or unassigned. DAG assignment can be done explicitly when the
operator is created, through deferred assignment, or even inferred from other
operators.
dag = DAG('my_dag', start_date=datetime(2016, 1, 1))
# sets the DAG explicitly
explicit_op = DummyOperator(task_id='op1', dag=dag)
# deferred DAG assignment
deferred_op = DummyOperator(task_id='op2')
deferred_op.dag = dag
# inferred DAG assignment (linked operators must be in the same DAG)
inferred_op = DummyOperator(task_id='op3')
inferred_op.set_upstream(deferred_op)
Bitshift Composition¶
Added in Airflow 1.8
We recommend you setting operator relationships with bitshift operators rather than set_upstream()
and set_downstream()
.
Traditionally, operator relationships are set with the set_upstream()
and
set_downstream()
methods. In Airflow 1.8, this can be done with the Python
bitshift operators >>
and <<
. The following four statements are all
functionally equivalent:
op1 >> op2
op1.set_downstream(op2)
op2 << op1
op2.set_upstream(op1)
When using the bitshift to compose operators, the relationship is set in the
direction that the bitshift operator points. For example, op1 >> op2
means
that op1
runs first and op2
runs second. Multiple operators can be
composed -- keep in mind the chain is executed left-to-right and the rightmost
object is always returned. For example:
op1 >> op2 >> op3 << op4
is equivalent to:
op1.set_downstream(op2)
op2.set_downstream(op3)
op3.set_upstream(op4)
We can put this all together to build a simple pipeline:
with DAG('my_dag', start_date=datetime(2016, 1, 1)) as dag:
(
DummyOperator(task_id='dummy_1')
>> BashOperator(
task_id='bash_1',
bash_command='echo "HELLO!"')
>> PythonOperator(
task_id='python_1',
python_callable=lambda: print("GOODBYE!"))
)
Bitshift can also be used with lists. For example:
op1 >> [op2, op3] >> op4
is equivalent to:
op1 >> op2 >> op4
op1 >> op3 >> op4
and equivalent to:
op1.set_downstream([op2, op3])
op4.set_upstream([op2, op3])
Relationship Builders¶
Moved in Airflow 2.0
chain
and cross_downstream
function provide easier ways to set relationships
between operators in specific situation.
In Airflow 2.0 those two methods moved from airflow.utils.helpers
to airflow.models.baseoperator
.
When setting a relationship between two lists, if we want all operators in one list to be upstream to all operators in the other, we cannot use a single bitshift composition. Instead we have to split one of the lists:
[op1, op2, op3] >> op4
[op1, op2, op3] >> op5
[op1, op2, op3] >> op6
cross_downstream
could handle list relationships easier.
cross_downstream([op1, op2, op3], [op4, op5, op6])
When setting single direction relationships to many operators, we could concat them with bitshift composition.
op1 >> op2 >> op3 >> op4 >> op5
This can be accomplished using chain
chain(op1, op2, op3, op4, op5)
even without operator's name
chain([DummyOperator(task_id='op' + i, dag=dag) for i in range(1, 6)])
chain
can handle a list of operators
chain(op1, [op2, op3], op4)
is equivalent to:
op1 >> [op2, op3] >> op4
When chain
sets relationships between two lists of operators, they must have the same size.
chain(op1, [op2, op3], [op4, op5], op6)
is equivalent to:
op1 >> [op2, op3]
op2 >> op4
op3 >> op5
[op4, op5] >> op6
Workflows¶
You're now familiar with the core building blocks of Airflow. Some of the concepts may sound very similar, but the vocabulary can be conceptualized like this:
DAG: The work (tasks), and the order in which work should take place (dependencies), written in Python.
DAG Run: An instance of a DAG for a particular logical date and time.
Operator: A class that acts as a template for carrying out some work.
Task: Defines work by implementing an operator, written in Python.
Task Instance: An instance of a task - that has been assigned to a DAG and has a state associated with a specific DAG run (i.e. for a specific execution_date).
execution_date: The logical date and time for a DAG Run and its Task Instances.
By combining DAGs
and Operators
to create TaskInstances
, you can
build complex workflows.
Additional Functionality¶
In addition to the core Airflow objects, there are a number of more complex features that enable behaviors like limiting simultaneous access to resources, cross-communication, conditional execution, and more.
Hooks¶
Hooks are interfaces to external platforms and databases like Hive, S3,
MySQL, Postgres, HDFS, and Pig. Hooks implement a common interface when
possible, and act as a building block for operators. They also use
the airflow.models.connection.Connection
model to retrieve hostnames
and authentication information. Hooks keep authentication code and
information out of pipelines, centralized in the metadata database.
Hooks are also very useful on their own to use in Python scripts, Airflow airflow.operators.PythonOperator, and in interactive environments like iPython or Jupyter Notebook.
See also
Pools¶
Some systems can get overwhelmed when too many processes hit them at the same
time. Airflow pools can be used to limit the execution parallelism on
arbitrary sets of tasks. The list of pools is managed in the UI
(Menu -> Admin -> Pools
) by giving the pools a name and assigning
it a number of worker slots. Tasks can then be associated with
one of the existing pools by using the pool
parameter when
creating tasks (i.e., instantiating operators).
aggregate_db_message_job = BashOperator(
task_id='aggregate_db_message_job',
execution_timeout=timedelta(hours=3),
pool='ep_data_pipeline_db_msg_agg',
bash_command=aggregate_db_message_job_cmd,
dag=dag)
aggregate_db_message_job.set_upstream(wait_for_empty_queue)
The pool
parameter can
be used in conjunction with priority_weight
to define priorities
in the queue, and which tasks get executed first as slots open up in the
pool. The default priority_weight
is 1
, and can be bumped to any
number. When sorting the queue to evaluate which task should be executed
next, we use the priority_weight
, summed up with all of the
priority_weight
values from tasks downstream from this task. You can
use this to bump a specific important task and the whole path to that task
gets prioritized accordingly.
Tasks will be scheduled as usual while the slots fill up. Once capacity is
reached, runnable tasks get queued and their state will show as such in the
UI. As slots free up, queued tasks start running based on the
priority_weight
(of the task and its descendants).
Note that if tasks are not given a pool, they are assigned to a default
pool default_pool
. default_pool
is initialized with 128 slots and
can changed through the UI or CLI (though it cannot be removed).
To combine Pools with SubDAGs see the SubDAGs section.
Connections¶
The information needed to connect to external systems is stored in the Airflow metastore database and can be
managed in the UI (Menu -> Admin -> Connections
). A conn_id
is defined there, and hostname / login /
password / schema information attached to it. Airflow pipelines retrieve centrally-managed connections
information by specifying the relevant conn_id
.
Airflow also provides a mechanism to store connections outside the database, e.g. in environment variables. Additional sources may be enabled, e.g. AWS SSM Parameter Store, or you may roll your own secrets backend.
Many hooks have a default conn_id
, where operators using that hook do not
need to supply an explicit connection ID. For example, the default
conn_id
for the PostgresHook
is
postgres_default
.
See Managing Connections for details on creating and managing connections.
XComs¶
XComs let tasks exchange messages, allowing more nuanced forms of control and shared state. The name is an abbreviation of "cross-communication". XComs are principally defined by a key, value, and timestamp, but also track attributes like the task/DAG that created the XCom and when it should become visible. Any object that can be pickled can be used as an XCom value, so users should make sure to use objects of appropriate size.
XComs can be "pushed" (sent) or "pulled" (received). When a task pushes an
XCom, it makes it generally available to other tasks. Tasks can push XComs at
any time by calling the xcom_push()
method. In addition, if a task returns
a value (either from its Operator's execute()
method, or from a
PythonOperator's python_callable
function), then an XCom containing that
value is automatically pushed.
Tasks call xcom_pull()
to retrieve XComs, optionally applying filters
based on criteria like key
, source task_ids
, and source dag_id
. By
default, xcom_pull()
filters for the keys that are automatically given to
XComs when they are pushed by being returned from execute functions (as
opposed to XComs that are pushed manually).
If xcom_pull
is passed a single string for task_ids
, then the most
recent XCom value from that task is returned; if a list of task_ids
is
passed, then a corresponding list of XCom values is returned.
# inside a PythonOperator called 'pushing_task'
def push_function():
return value
# inside another PythonOperator
def pull_function(task_instance):
value = task_instance.xcom_pull(task_ids='pushing_task')
When specifying arguments that are part of the context, they will be automatically passed to the function.
It is also possible to pull XCom directly in a template, here's an example of what this may look like:
SELECT * FROM {{ task_instance.xcom_pull(task_ids='foo', key='table_name') }}
Note that XComs are similar to Variables, but are specifically designed for inter-task communication rather than global settings.
Custom XCom backend¶
It is possible to change XCom
behaviour of serialization and deserialization of tasks' result.
To do this one have to change xcom_backend
parameter in Airflow config. Provided value should point
to a class that is subclass of BaseXCom
. To alter the serialization /
deserialization mechanism the custom class should override serialize_value
and deserialize_value
methods.
It is also possible to override the orm_deserialize_value
method which is used for deserialization when
recreating ORM XCom object. This happens every time we query the XCom table, for example when we want to populate
XCom list view in webserver. If your XCom backend performs expensive operations, or has large values that are not
useful to show in such a view, override this method to provide an alternative representation. By default Airflow will
use BaseXCom.orm_deserialize_value
method which returns the value stored in Airflow database.
See Modules Management for details on how Python and Airflow manage modules.
Variables¶
Variables are a generic way to store and retrieve arbitrary content or
settings as a simple key value store within Airflow. Variables can be
listed, created, updated and deleted from the UI (Admin -> Variables
),
code or CLI. In addition, json settings files can be bulk uploaded through
the UI. While your pipeline code definition and most of your constants
and variables should be defined in code and stored in source control,
it can be useful to have some variables or configuration items
accessible and modifiable through the UI.
from airflow.models import Variable
foo = Variable.get("foo")
bar = Variable.get("bar", deserialize_json=True)
baz = Variable.get("baz", default_var=None)
The second call assumes json
content and will be deserialized into
bar
. Note that Variable
is a sqlalchemy model and can be used
as such. The third call uses the default_var
parameter with the value
None
, which either returns an existing value or None
if the variable
isn't defined. The get function will throw a KeyError
if the variable
doesn't exist and no default is provided.
You can use a variable from a jinja template with the syntax :
echo {{ var.value.<variable_name> }}
or if you need to deserialize a json object from the variable :
echo {{ var.json.<variable_name> }}
See Managing Variables for details on managing variables.
Branching¶
Sometimes you need a workflow to branch, or only go down a certain path
based on an arbitrary condition which is typically related to something
that happened in an upstream task. One way to do this is by using the
BranchPythonOperator
.
The BranchPythonOperator
is much like the PythonOperator except that it
expects a python_callable
that returns a task_id (or list of task_ids). The
task_id returned is followed, and all of the other paths are skipped.
The task_id returned by the Python function has to reference a task
directly downstream from the BranchPythonOperator task.
Note that when a path is a downstream task of the returned task (list), it will not be skipped:
Paths of the branching task are branch_a
, join
and branch_b
. Since
join
is a downstream task of branch_a
, it will be excluded from the skipped
tasks when branch_a
is returned by the Python callable.
The BranchPythonOperator
can also be used with XComs allowing branching
context to dynamically decide what branch to follow based on upstream tasks.
For example:
def branch_func(ti):
xcom_value = int(ti.xcom_pull(task_ids='start_task'))
if xcom_value >= 5:
return 'continue_task'
else:
return 'stop_task'
start_op = BashOperator(
task_id='start_task',
bash_command="echo 5",
xcom_push=True,
dag=dag)
branch_op = BranchPythonOperator(
task_id='branch_task',
python_callable=branch_func,
dag=dag)
continue_op = DummyOperator(task_id='continue_task', dag=dag)
stop_op = DummyOperator(task_id='stop_task', dag=dag)
start_op >> branch_op >> [continue_op, stop_op]
If you wish to implement your own operators with branching functionality, you
can inherit from BaseBranchOperator
,
which behaves similarly to BranchPythonOperator
but expects you to provide
an implementation of the method choose_branch
. As with the callable for
BranchPythonOperator
, this method should return the ID of a downstream task,
or a list of task IDs, which will be run, and all others will be skipped.
class MyBranchOperator(BaseBranchOperator):
def choose_branch(self, context):
"""
Run an extra branch on the first day of the month
"""
if context['execution_date'].day == 1:
return ['daily_task_id', 'monthly_task_id']
else:
return 'daily_task_id'
SubDAGs¶
SubDAGs are perfect for repeating patterns. Defining a function that returns a DAG object is a nice design pattern when using Airflow.
Airbnb uses the stage-check-exchange pattern when loading data. Data is staged in a temporary table, after which data quality checks are performed against that table. Once the checks all pass the partition is moved into the production table.
As another example, consider the following DAG:
We can combine all of the parallel task-*
operators into a single SubDAG,
so that the resulting DAG resembles the following:
Note that SubDAG operators should contain a factory method that returns a DAG object. This will prevent the SubDAG from being treated like a separate DAG in the main UI. For example:
from airflow import DAG
from airflow.operators.dummy import DummyOperator
from airflow.utils.dates import days_ago
def subdag(parent_dag_name, child_dag_name, args):
"""
Generate a DAG to be used as a subdag.
:param str parent_dag_name: Id of the parent DAG
:param str child_dag_name: Id of the child DAG
:param dict args: Default arguments to provide to the subdag
:return: DAG to use as a subdag
:rtype: airflow.models.DAG
"""
dag_subdag = DAG(
dag_id=f'{parent_dag_name}.{child_dag_name}',
default_args=args,
start_date=days_ago(2),
schedule_interval="@daily",
)
for i in range(5):
DummyOperator(
task_id='{}-task-{}'.format(child_dag_name, i + 1),
default_args=args,
dag=dag_subdag,
)
return dag_subdag
This SubDAG can then be referenced in your main DAG file:
airflow/example_dags/example_subdag_operator.py
from airflow import DAG
from airflow.example_dags.subdags.subdag import subdag
from airflow.operators.dummy import DummyOperator
from airflow.operators.subdag import SubDagOperator
from airflow.utils.dates import days_ago
DAG_NAME = 'example_subdag_operator'
args = {
'owner': 'airflow',
}
with DAG(
dag_id=DAG_NAME, default_args=args, start_date=days_ago(2), schedule_interval="@once", tags=['example']
) as dag:
start = DummyOperator(
task_id='start',
)
section_1 = SubDagOperator(
task_id='section-1',
subdag=subdag(DAG_NAME, 'section-1', args),
)
some_other_task = DummyOperator(
task_id='some-other-task',
)
section_2 = SubDagOperator(
task_id='section-2',
subdag=subdag(DAG_NAME, 'section-2', args),
)
end = DummyOperator(
task_id='end',
)
start >> section_1 >> some_other_task >> section_2 >> end
You can zoom into a SubDagOperator
from the graph view of the main DAG to show
the tasks contained within the SubDAG:
Some other tips when using SubDAGs:
by convention, a SubDAG's
dag_id
should be prefixed by its parent and a dot. As inparent.child
share arguments between the main DAG and the SubDAG by passing arguments to the SubDAG operator (as demonstrated above)
SubDAGs must have a schedule and be enabled. If the SubDAG's schedule is set to
None
or@once
, the SubDAG will succeed without having done anythingclearing a
SubDagOperator
also clears the state of the tasks withinmarking success on a
SubDagOperator
does not affect the state of the tasks withinrefrain from using
depends_on_past=True
in tasks within the SubDAG as this can be confusingit is possible to specify an executor for the SubDAG. It is common to use the SequentialExecutor if you want to run the SubDAG in-process and effectively limit its parallelism to one. Using LocalExecutor can be problematic as it may over-subscribe your worker, running multiple tasks in a single slot
See airflow/example_dags
for a demonstration.
Note that airflow pool is not honored by SubDagOperator
. Hence
resources could be consumed by SubdagOperators.
TaskGroup¶
TaskGroup can be used to organize tasks into hierarchical groups in Graph View. It is
useful for creating repeating patterns and cutting down visual clutter. Unlike
SubDagOperator
, TaskGroup is a UI grouping concept.
Tasks in TaskGroups live on the same original DAG. They honor all the pool configurations.
Dependency relationships can be applied across all tasks in a TaskGroup with the >>
and <<
operators. For example, the following code puts task1
and task2
in TaskGroup group1
and then puts both tasks upstream of task3
:
with TaskGroup("group1") as group1:
task1 = DummyOperator(task_id="task1")
task2 = DummyOperator(task_id="task2")
task3 = DummyOperator(task_id="task3")
group1 >> task3
Note
By default, child tasks and TaskGroups have their task_id and group_id prefixed with the
group_id of their parent TaskGroup. This ensures uniqueness of group_id and task_id throughout
the DAG. To disable the prefixing, pass prefix_group_id=False
when creating the TaskGroup.
This then gives the user full control over the actual group_id and task_id. They have to ensure
group_id and task_id are unique throughout the DAG. The option prefix_group_id=False
is
mainly useful for putting tasks on existing DAGs into TaskGroup without altering their task_id.
Here is a more complicated example DAG with multiple levels of nested TaskGroups:
with DAG(dag_id="example_task_group", start_date=days_ago(2), tags=["example"]) as dag:
start = DummyOperator(task_id="start")
# [START howto_task_group_section_1]
with TaskGroup("section_1", tooltip="Tasks for section_1") as section_1:
task_1 = DummyOperator(task_id="task_1")
task_2 = BashOperator(task_id="task_2", bash_command='echo 1')
task_3 = DummyOperator(task_id="task_3")
task_1 >> [task_2, task_3]
# [END howto_task_group_section_1]
# [START howto_task_group_section_2]
with TaskGroup("section_2", tooltip="Tasks for section_2") as section_2:
task_1 = DummyOperator(task_id="task_1")
# [START howto_task_group_inner_section_2]
with TaskGroup("inner_section_2", tooltip="Tasks for inner_section2") as inner_section_2:
task_2 = BashOperator(task_id="task_2", bash_command='echo 1')
task_3 = DummyOperator(task_id="task_3")
task_4 = DummyOperator(task_id="task_4")
[task_2, task_3] >> task_4
# [END howto_task_group_inner_section_2]
# [END howto_task_group_section_2]
end = DummyOperator(task_id='end')
start >> section_1 >> section_2 >> end
This animated gif shows the UI interactions. TaskGroups are expanded or collapsed when clicked:
SLAs¶
Service Level Agreements, or time by which a task or DAG should have
succeeded, can be set at a task level as a timedelta
. If
one or many instances have not succeeded by that time, an alert email is sent
detailing the list of tasks that missed their SLA. The event is also recorded
in the database and made available in the web UI under Browse->SLA Misses
where events can be analyzed and documented.
SLAs can be configured for scheduled tasks by using the sla
parameter.
In addition to sending alerts to the addresses specified in a task's email
parameter,
the sla_miss_callback
specifies an additional Callable
object to be invoked when the SLA is not met.
If you don't want to check SLAs, you can disable globally (all the DAGs) by
setting check_slas=False
under [core]
section in airflow.cfg
file:
[core]
check_slas = False
Note
For information on the email configuration, see Email Configuration
Trigger Rules¶
Though the normal workflow behavior is to trigger tasks when all their directly upstream tasks have succeeded, Airflow allows for more complex dependency settings.
All operators have a trigger_rule
argument which defines the rule by which
the generated task get triggered. The default value for trigger_rule
is
all_success
and can be defined as "trigger this task when all directly
upstream tasks have succeeded". All other rules described here are based
on direct parent tasks and are values that can be passed to any operator
while creating tasks:
all_success
: (default) all parents have succeededall_failed
: all parents are in afailed
orupstream_failed
stateall_done
: all parents are done with their executionone_failed
: fires as soon as at least one parent has failed, it does not wait for all parents to be doneone_success
: fires as soon as at least one parent succeeds, it does not wait for all parents to be donenone_failed
: all parents have not failed (failed
orupstream_failed
) i.e. all parents have succeeded or been skippednone_failed_or_skipped
: all parents have not failed (failed
orupstream_failed
) and at least one parent has succeeded.none_skipped
: no parent is in askipped
state, i.e. all parents are in asuccess
,failed
, orupstream_failed
statedummy
: dependencies are just for show, trigger at will
Note that these can be used in conjunction with depends_on_past
(boolean)
that, when set to True
, keeps a task from getting triggered if the
previous schedule for the task hasn't succeeded.
One must be aware of the interaction between trigger rules and skipped tasks
in schedule level. Skipped tasks will cascade through trigger rules
all_success
and all_failed
but not all_done
, one_failed
, one_success
,
none_failed
, none_failed_or_skipped
, none_skipped
and dummy
.
For example, consider the following DAG:
#dags/branch_without_trigger.py
import datetime as dt
from airflow.models import DAG
from airflow.operators.dummy import DummyOperator
from airflow.operators.python import BranchPythonOperator
dag = DAG(
dag_id='branch_without_trigger',
schedule_interval='@once',
start_date=dt.datetime(2019, 2, 28)
)
run_this_first = DummyOperator(task_id='run_this_first', dag=dag)
branching = BranchPythonOperator(
task_id='branching', dag=dag,
python_callable=lambda: 'branch_a'
)
branch_a = DummyOperator(task_id='branch_a', dag=dag)
follow_branch_a = DummyOperator(task_id='follow_branch_a', dag=dag)
branch_false = DummyOperator(task_id='branch_false', dag=dag)
join = DummyOperator(task_id='join', dag=dag)
run_this_first >> branching
branching >> branch_a >> follow_branch_a >> join
branching >> branch_false >> join
In the case of this DAG, join
is downstream of follow_branch_a
and branch_false
. The join
task will show up as skipped
because its trigger_rule
is set to all_success
by default and
skipped tasks will cascade through all_success
.
By setting trigger_rule
to none_failed_or_skipped
in join
task,
#dags/branch_with_trigger.py
...
join = DummyOperator(task_id='join', dag=dag, trigger_rule='none_failed_or_skipped')
...
The join
task will be triggered as soon as
branch_false
has been skipped (a valid completion state) and
follow_branch_a
has succeeded. Because skipped tasks will not
cascade through none_failed_or_skipped
.
Latest Run Only¶
Standard workflow behavior involves running a series of tasks for a particular date/time range. Some workflows, however, perform tasks that are independent of run time but need to be run on a schedule, much like a standard cron job. In these cases, backfills or running jobs missed during a pause just wastes CPU cycles.
For situations like this, you can use the LatestOnlyOperator
to skip
tasks that are not being run during the most recent scheduled run for a
DAG. The LatestOnlyOperator
skips all direct downstream tasks, if the time
right now is not between its execution_time
and the next scheduled
execution_time
or the DagRun has been externally triggered.
For example, consider the following DAG:
import datetime as dt
from airflow import DAG
from airflow.operators.dummy import DummyOperator
from airflow.operators.latest_only import LatestOnlyOperator
from airflow.utils.dates import days_ago
from airflow.utils.trigger_rule import TriggerRule
with DAG(
dag_id='latest_only_with_trigger',
schedule_interval=dt.timedelta(hours=4),
start_date=days_ago(2),
tags=['example3'],
) as dag:
latest_only = LatestOnlyOperator(task_id='latest_only')
task1 = DummyOperator(task_id='task1')
task2 = DummyOperator(task_id='task2')
task3 = DummyOperator(task_id='task3')
task4 = DummyOperator(task_id='task4', trigger_rule=TriggerRule.ALL_DONE)
latest_only >> task1 >> [task3, task4]
task2 >> [task3, task4]
In the case of this DAG, the task task1
is directly downstream of
latest_only
and will be skipped for all runs except the latest.
task2
is entirely independent of latest_only
and will run in all
scheduled periods. task3
is downstream of task1
and task2
and
because of the default trigger_rule
being all_success
will receive
a cascaded skip from task1
. task4
is downstream of task1
and
task2
, but it will not be skipped, since its trigger_rule
is set to
all_done
.
Zombies & Undeads¶
Task instances die all the time, usually as part of their normal life cycle, but sometimes unexpectedly.
Zombie tasks are characterized by the absence
of a heartbeat (emitted by the job periodically) and a running
status
in the database. They can occur when a worker node can't reach the database,
when Airflow processes are killed externally, or when a node gets rebooted
for instance. Zombie killing is performed periodically by the scheduler's
process.
Undead processes are characterized by the existence of a process and a matching
heartbeat, but Airflow isn't aware of this task as running
in the database.
This mismatch typically occurs as the state of the database is altered,
most likely by deleting rows in the "Task Instances" view in the UI.
Tasks are instructed to verify their state as part of the heartbeat routine,
and terminate themselves upon figuring out that they are in this "undead"
state.
Cluster Policy¶
Cluster policies provide an interface for taking action on every Airflow task or DAG either at DAG load time or just before task execution. In this way users are able to do the following:
set default arguments on each DAG/task
checks that DAG/task meets required standards
perform custom logic of routing task to a queue
And many other options. To use cluster-wide policies users can define in their
airflow_local_settings
the following functions
dag_policy
- which as an input takesdag
argument ofDAG
type. This function allows users to define dag-level policy which is executed for every DAG at loading time.task_policy
- which as an input takestask
argument ofBaseOperator
type. This function allows users to define task-level policy which is executed for every task at DAG loading time.task_instance_mutation_hook
- which as an input takestask_instance
argument ofTaskInstance
type. This function allows users to define task-level policy that is executed right before the task execution.
In case of DAG and task policies users may raise AirflowClusterPolicyViolation
to prevent a DAG from being imported or prevent a task from being executed if the task is not compliant with
users' check.
Please note, cluster policy will have precedence over task attributes defined in DAG meaning that
if task.sla
is defined in dag and also mutated via cluster policy then the latter will have precedence.
In next sections we show examples of each type of cluster policy.
Where to put airflow_local_settings.py
?¶
Add a airflow_local_settings.py
file to your $PYTHONPATH
or to $AIRFLOW_HOME/config
folder.
See Modules Management for details on how Python and Airflow manage modules.
DAG level cluster policy¶
In this example we check if each DAG has at least one tag defined. Here is what it may look like:
def dag_policy(dag: DAG):
"""Ensure that DAG has at least one tag"""
if not dag.tags:
raise AirflowClusterPolicyViolation(
f"DAG {dag.dag_id} has no tags. At least one tag required. File path: {dag.filepath}"
)
Task level cluster policy¶
For example, this function could apply a specific queue property when using a specific operator, or enforce a task timeout policy, making sure that no tasks run for more than 48 hours. Here's an example of what this may look like:
def task_policy(task: BaseOperator):
if task.task_type == 'HivePartitionSensor':
task.queue = "sensor_queue"
if task.timeout > timedelta(hours=48):
task.timeout = timedelta(hours=48)
As a more advanced example we may consider implementing checks that are intended to help teams using Airflow to protect against common beginner errors that may get past a code reviewer, rather than as technical security controls.
For example, don't run tasks without airflow owners:
def task_must_have_owners(task: BaseOperator):
if not task.owner or task.owner.lower() == conf.get('operators', 'default_owner'):
raise AirflowClusterPolicyViolation(
f'''Task must have non-None non-default owner. Current value: {task.owner}'''
)
If you have multiple checks to apply, it is best practice to curate these rules
in a separate python module and have a single policy / task mutation hook that
performs multiple of these custom checks and aggregates the various error
messages so that a single AirflowClusterPolicyViolation
can be reported in
the UI (and import errors table in the database).
For Example in airflow_local_settings.py
:
TASK_RULES: List[Callable[[BaseOperator], None]] = [
task_must_have_owners,
]
def _check_task_rules(current_task: BaseOperator):
"""Check task rules for given task."""
notices = []
for rule in TASK_RULES:
try:
rule(current_task)
except AirflowClusterPolicyViolation as ex:
notices.append(str(ex))
if notices:
notices_list = " * " + "\n * ".join(notices)
raise AirflowClusterPolicyViolation(
f"DAG policy violation (DAG ID: {current_task.dag_id}, Path: {current_task.dag.filepath}):\n"
f"Notices:\n"
f"{notices_list}"
)
def cluster_policy(task: BaseOperator):
"""Ensure Tasks have non-default owners."""
_check_task_rules(task)
Task instance mutation hook¶
Task instance mutation hook can be used for example to re-routes the task to execute in a different queue during retries:
def task_instance_mutation_hook(task_instance: TaskInstance):
if task_instance.try_number >= 1:
task_instance.queue = 'retry_queue'
Documentation & Notes¶
It's possible to add documentation or notes to your DAGs & task objects that become visible in the web interface ("Graph View" & "Tree View" for DAGs, "Task Instance Details" for tasks). There are a set of special task attributes that get rendered as rich content if defined:
attribute |
rendered to |
---|---|
doc |
monospace |
doc_json |
json |
doc_yaml |
yaml |
doc_md |
markdown |
doc_rst |
reStructuredText |
Please note that for DAGs, doc_md is the only attribute interpreted.
This is especially useful if your tasks are built dynamically from configuration files, it allows you to expose the configuration that led to the related tasks in Airflow.
"""
### My great DAG
"""
dag = DAG('my_dag', default_args=default_args)
dag.doc_md = __doc__
t = BashOperator("foo", dag=dag)
t.doc_md = """\
#Title"
Here's a [url](www.airbnb.com)
"""
This content will get rendered as markdown respectively in the "Graph View" and "Task Instance Details" pages.
Jinja Templating¶
Airflow leverages the power of Jinja Templating and this can be a powerful tool to use in combination with macros (see the Macros reference section).
For example, say you want to pass the execution date as an environment variable
to a Bash script using the BashOperator
.
# The execution date as YYYY-MM-DD
date = "{{ ds }}"
t = BashOperator(
task_id='test_env',
bash_command='/tmp/test.sh ',
dag=dag,
env={'EXECUTION_DATE': date})
Here, {{ ds }}
is a macro, and because the env
parameter of the
BashOperator
is templated with Jinja, the execution date will be available
as an environment variable named EXECUTION_DATE
in your Bash script.
You can use Jinja templating with every parameter that is marked as "templated" in the documentation. Template substitution occurs just before the pre_execute function of your operator is called.
You can also use Jinja templating with nested fields, as long as these nested fields
are marked as templated in the structure they belong to: fields registered in
template_fields
property will be submitted to template substitution, like the
path
field in the example below:
class MyDataReader:
template_fields = ['path']
def __init__(self, my_path):
self.path = my_path
# [additional code here...]
t = PythonOperator(
task_id='transform_data',
python_callable=transform_data
op_args=[
MyDataReader('/tmp/{{ ds }}/my_file')
],
dag=dag)
Note
template_fields
property can equally be a class variable or an
instance variable.
Deep nested fields can also be substituted, as long as all intermediate fields are marked as template fields:
class MyDataTransformer:
template_fields = ['reader']
def __init__(self, my_reader):
self.reader = my_reader
# [additional code here...]
class MyDataReader:
template_fields = ['path']
def __init__(self, my_path):
self.path = my_path
# [additional code here...]
t = PythonOperator(
task_id='transform_data',
python_callable=transform_data
op_args=[
MyDataTransformer(MyDataReader('/tmp/{{ ds }}/my_file'))
],
dag=dag)
You can pass custom options to the Jinja Environment
when creating your DAG.
One common usage is to avoid Jinja from dropping a trailing newline from a
template string:
my_dag = DAG(dag_id='my-dag',
jinja_environment_kwargs={
'keep_trailing_newline': True,
# some other jinja2 Environment options here
})
See Jinja documentation to find all available options.
Exceptions¶
Airflow defines a number of exceptions; most of these are used internally, but a few
are relevant to authors of custom operators or Python callables called from PythonOperator
tasks. Normally any exception raised from an execute
method or Python callable will either
cause a task instance to fail if it is not configured to retry or has reached its limit on
retry attempts, or to be marked as "up for retry". A few exceptions can be used when different
behavior is desired:
AirflowSkipException
can be raised to set the state of the current task instance to "skipped"AirflowFailException
can be raised to set the state of the current task to "failed" regardless of whether there are any retry attempts remaining.
This example illustrates some possibilities
from airflow.exceptions import AirflowFailException, AirflowSkipException
def fetch_data():
try:
data = get_some_data(get_api_key())
if not data:
# Set state to skipped and do not retry
# Downstream task behavior will be determined by trigger rules
raise AirflowSkipException("No data available.")
except Unauthorized:
# If we retry, our api key will still be bad, so don't waste time retrying!
# Set state to failed and move on
raise AirflowFailException("Our api key is bad!")
except TransientError:
print("Looks like there was a blip.")
# Raise the exception and let the task retry unless max attempts were reached
raise
handle(data)
task = PythonOperator(task_id="fetch_data", python_callable=fetch_data, retries=10)
See also
Packaged DAGs¶
While often you will specify DAGs in a single .py
file it might sometimes
be required to combine a DAG and its dependencies. For example, you might want
to combine several DAGs together to version them together or you might want
to manage them together or you might need an extra module that is not available
by default on the system you are running Airflow on. To allow this you can create
a zip file that contains the DAG(s) in the root of the zip file and have the extra
modules unpacked in directories.
For instance you can create a zip file that looks like this:
my_dag1.py
my_dag2.py
package1/__init__.py
package1/functions.py
Airflow will scan the zip file and try to load my_dag1.py
and my_dag2.py
.
It will not go into subdirectories as these are considered to be potential
packages.
In case you would like to add module dependencies to your DAG you basically would do the same, but then it is more suitable to use a virtualenv and pip.
virtualenv zip_dag
source zip_dag/bin/activate
mkdir zip_dag_contents
cd zip_dag_contents
pip install --install-option="--install-lib=$PWD" my_useful_package
cp ~/my_dag.py .
zip -r zip_dag.zip *
Note
the zip file will be inserted at the beginning of module search list (sys.path) and as such it will be available to any other code that resides within the same interpreter.
Note
packaged dags cannot be used with pickling turned on.
Note
packaged dags cannot contain dynamic libraries (eg. libz.so) these need to be available on the system if a module needs those. In other words only pure Python modules can be packaged.
.airflowignore
¶
A .airflowignore
file specifies the directories or files in DAG_FOLDER
or PLUGINS_FOLDER
that Airflow should intentionally ignore.
Each line in .airflowignore
specifies a regular expression pattern,
and directories or files whose names (not DAG id) match any of the patterns
would be ignored (under the hood, Pattern.search()
is used to match the pattern).
Overall it works like a .gitignore
file.
Use the #
character to indicate a comment; all characters
on a line following a #
will be ignored.
.airflowignore
file should be put in your DAG_FOLDER
.
For example, you can prepare a .airflowignore
file with contents
project_a
tenant_[\d]
Then files like project_a_dag_1.py
, TESTING_project_a.py
, tenant_1.py
,
project_a/dag_1.py
, and tenant_1/dag_1.py
in your DAG_FOLDER
would be ignored
(If a directory's name matches any of the patterns, this directory and all its subfolders
would not be scanned by Airflow at all. This improves efficiency of DAG finding).
The scope of a .airflowignore
file is the directory it is in plus all its subfolders.
You can also prepare .airflowignore
file for a subfolder in DAG_FOLDER
and it
would only be applicable for that subfolder.