Configuration

Setting up the sandbox in the Quick Start section was easy; building a production-grade environment requires a bit more work!

Setting Configuration Options

The first time you run Airflow, it will create a file called airflow.cfg in your $AIRFLOW_HOME directory (~/airflow by default). This file contains Airflow’s configuration and you can edit it to change any of the settings. You can also set options with environment variables by using this format: $AIRFLOW__{SECTION}__{KEY} (note the double underscores).

For example, the metadata database connection string can either be set in airflow.cfg like this:

[core]
sql_alchemy_conn = my_conn_string

or by creating a corresponding environment variable:

AIRFLOW__CORE__SQL_ALCHEMY_CONN=my_conn_string

You can also derive the connection string at run time by appending _cmd to the key like this:

[core]
sql_alchemy_conn_cmd = bash_command_to_run

But only three such configuration elements namely sql_alchemy_conn, broker_url and celery_result_backend can be fetched as a command. The idea behind this is to not store passwords on boxes in plain text files. The order of precedence is as follows -

  1. environment variable
  2. configuration in airflow.cfg
  3. command in airflow.cfg
  4. default

Setting up a Backend

If you want to take a real test drive of Airflow, you should consider setting up a real database backend and switching to the LocalExecutor.

As Airflow was built to interact with its metadata using the great SqlAlchemy library, you should be able to use any database backend supported as a SqlAlchemy backend. We recommend using MySQL or Postgres.

Note

If you decide to use Postgres, we recommend using the psycopg2 driver and specifying it in your SqlAlchemy connection string. Also note that since SqlAlchemy does not expose a way to target a specific schema in the Postgres connection URI, you may want to set a default schema for your role with a command similar to ALTER ROLE username SET search_path = airflow, foobar;

Once you’ve setup your database to host Airflow, you’ll need to alter the SqlAlchemy connection string located in your configuration file $AIRFLOW_HOME/airflow.cfg. You should then also change the “executor” setting to use “LocalExecutor”, an executor that can parallelize task instances locally.

# initialize the database
airflow initdb

Connections

Airflow needs to know how to connect to your environment. Information such as hostname, port, login and passwords to other systems and services is handled in the Admin->Connection section of the UI. The pipeline code you will author will reference the ‘conn_id’ of the Connection objects.

_images/connections.png

By default, Airflow will save the passwords for the connection in plain text within the metadata database. The crypto package is highly recommended during installation. The crypto package does require that your operating system have libffi-dev installed.

If crypto package was not installed initially, you can still enable encryption for connections by following steps below:

  1. Install crypto package pip install airflow[crypto]
  2. Generate fernet_key, using this code snippet below. fernet_key must be a base64-encoded 32-byte key.
from cryptography.fernet import Fernet
fernet_key= Fernet.generate_key()
print(fernet_key) # your fernet_key, keep it in secured place!

3. Replace airflow.cfg fernet_key value with the one from step 2. Alternatively, you can store your fernet_key in OS environment variable. You do not need to change airflow.cfg in this case as AirFlow will use environment variable over the value in airflow.cfg:

# Note the double underscores
EXPORT AIRFLOW__CORE__FERNET_KEY = your_fernet_key
  1. Restart AirFlow webserver.
  2. For existing connections (the ones that you had defined before installing airflow[crypto] and creating a Fernet key), you need to open each connection in the connection admin UI, re-type the password, and save it.

Connections in Airflow pipelines can be created using environment variables. The environment variable needs to have a prefix of AIRFLOW_CONN_ for Airflow with the value in a URI format to use the connection properly. Please see the Concepts documentation for more information on environment variables and connections.

Scaling Out with Celery

CeleryExecutor is one of the ways you can scale out the number of workers. For this to work, you need to setup a Celery backend (RabbitMQ, Redis, ...) and change your airflow.cfg to point the executor parameter to CeleryExecutor and provide the related Celery settings.

For more information about setting up a Celery broker, refer to the exhaustive Celery documentation on the topic.

Here are a few imperative requirements for your workers:

  • airflow needs to be installed, and the CLI needs to be in the path
  • Airflow configuration settings should be homogeneous across the cluster
  • Operators that are executed on the worker need to have their dependencies met in that context. For example, if you use the HiveOperator, the hive CLI needs to be installed on that box, or if you use the MySqlOperator, the required Python library needs to be available in the PYTHONPATH somehow
  • The worker needs to have access to its DAGS_FOLDER, and you need to synchronize the filesystems by your own means. A common setup would be to store your DAGS_FOLDER in a Git repository and sync it across machines using Chef, Puppet, Ansible, or whatever you use to configure machines in your environment. If all your boxes have a common mount point, having your pipelines files shared there should work as well

To kick off a worker, you need to setup Airflow and kick off the worker subcommand

airflow worker

Your worker should start picking up tasks as soon as they get fired in its direction.

Note that you can also run “Celery Flower”, a web UI built on top of Celery, to monitor your workers. You can use the shortcut command airflow flower to start a Flower web server.

Scaling Out with Dask

DaskExecutor allows you to run Airflow tasks in a Dask Distributed cluster.

Dask clusters can be run on a single machine or on remote networks. For complete details, consult the Distributed documentation.

To create a cluster, first start a Scheduler:

# default settings for a local cluster
DASK_HOST=127.0.0.1
DASK_PORT=8786

dask-scheduler --host $DASK_HOST --port $DASK_PORT

Next start at least one Worker on any machine that can connect to the host:

dask-worker $DASK_HOST:$DASK_PORT

Edit your airflow.cfg to set your executor to DaskExecutor and provide the Dask Scheduler address in the [dask] section.

Please note:

  • Each Dask worker must be able to import Airflow and any dependencies you require.
  • Dask does not support queues. If an Airflow task was created with a queue, a warning will be raised but the task will be submitted to the cluster.

Logs

Users can specify a logs folder in airflow.cfg. By default, it is in the AIRFLOW_HOME directory.

In addition, users can supply a remote location for storing logs and log backups in cloud storage. At this time, Amazon S3 and Google Cloud Storage are supported. To enable this feature, airflow.cfg must be configured as in this example:

[core]
# Airflow can store logs remotely in AWS S3 or Google Cloud Storage. Users
# must supply a remote location URL (starting with either 's3://...' or
# 'gs://...') and an Airflow connection id that provides access to the storage
# location.
remote_base_log_folder = s3://my-bucket/path/to/logs
remote_log_conn_id = MyS3Conn
# Use server-side encryption for logs stored in S3
encrypt_s3_logs = False

Remote logging uses an existing Airflow connection to read/write logs. If you don’t have a connection properly setup, this will fail. In the above example, Airflow will try to use S3Hook('MyS3Conn').

In the Airflow Web UI, local logs take precedance over remote logs. If local logs can not be found or accessed, the remote logs will be displayed. Note that logs are only sent to remote storage once a task completes (including failure). In other words, remote logs for running tasks are unavailable.

Scaling Out on Mesos (community contributed)

MesosExecutor allows you to schedule airflow tasks on a Mesos cluster. For this to work, you need a running mesos cluster and you must perform the following steps -

  1. Install airflow on a machine where web server and scheduler will run, let’s refer to this as the “Airflow server”.
  2. On the Airflow server, install mesos python eggs from mesos downloads.
  3. On the Airflow server, use a database (such as mysql) which can be accessed from mesos slave machines and add configuration in airflow.cfg.
  4. Change your airflow.cfg to point executor parameter to MesosExecutor and provide related Mesos settings.
  5. On all mesos slaves, install airflow. Copy the airflow.cfg from Airflow server (so that it uses same sql alchemy connection).
  6. On all mesos slaves, run the following for serving logs:
airflow serve_logs
  1. On Airflow server, to start processing/scheduling DAGs on mesos, run:
airflow scheduler -p

Note: We need -p parameter to pickle the DAGs.

You can now see the airflow framework and corresponding tasks in mesos UI. The logs for airflow tasks can be seen in airflow UI as usual.

For more information about mesos, refer to mesos documentation. For any queries/bugs on MesosExecutor, please contact @kapil-malik.

Integration with systemd

Airflow can integrate with systemd based systems. This makes watching your daemons easy as systemd can take care of restarting a daemon on failure. In the scripts/systemd directory you can find unit files that have been tested on Redhat based systems. You can copy those to /usr/lib/systemd/system. It is assumed that Airflow will run under airflow:airflow. If not (or if you are running on a non Redhat based system) you probably need to adjust the unit files.

Environment configuration is picked up from /etc/sysconfig/airflow. An example file is supplied. Make sure to specify the SCHEDULER_RUNS variable in this file when you run the scheduler. You can also define here, for example, AIRFLOW_HOME or AIRFLOW_CONFIG.

Integration with upstart

Airflow can integrate with upstart based systems. Upstart automatically starts all airflow services for which you have a corresponding *.conf file in /etc/init upon system boot. On failure, upstart automatically restarts the process (until it reaches re-spawn limit set in a *.conf file).

You can find sample upstart job files in the scripts/upstart directory. These files have been tested on Ubuntu 14.04 LTS. You may have to adjust start on and stop on stanzas to make it work on other upstart systems. Some of the possible options are listed in scripts/upstart/README.

Modify *.conf files as needed and copy to /etc/init directory. It is assumed that airflow will run under airflow:airflow. Change setuid and setgid in *.conf files if you use other user/group

You can use initctl to manually start, stop, view status of the airflow process that has been integrated with upstart

initctl airflow-webserver status

Test Mode

Airflow has a fixed set of “test mode” configuration options. You can load these at any time by calling airflow.configuration.load_test_config() (note this operation is not reversible!). However, some options (like the DAG_FOLDER) are loaded before you have a chance to call load_test_config(). In order to eagerly load the test configuration, set test_mode in airflow.cfg:

[tests]
unit_test_mode = True

Due to Airflow’s automatic environment variable expansion (see Setting Configuration Options), you can also set the env var AIRFLOW__CORE__UNIT_TEST_MODE to temporarily overwrite airflow.cfg.