Warning

The ECS Executor is alpha/experimental at the moment and may be subject to change without warning.

AWS ECS Executor

This is an Airflow executor powered by Amazon Elastic Container Service (ECS). Each task that Airflow schedules for execution is run within its own ECS container. Some benefits of an executor like this include:

  1. Task isolation: No task can be a noisy neighbor for another. Resources like CPU, memory and disk are isolated to each individual task. Any actions or failures which affect networking or fail the entire container only affect the single task running in it. No single user can overload the environment by triggering too many tasks, because there are no shared workers.

  2. Customized environments: You can build different container images which incorporate specific dependencies (such as system level dependencies), binaries, or data required for a task to run.

  3. Cost effective: Compute resources only exist for the lifetime of the Airflow task itself. This saves costs by not requiring persistent/long lived workers ready at all times, which also need maintenance and patching.

For a quick start guide please see here, it will get you up and running with a basic configuration.

The below sections provide more generic details about configuration, the provided example Dockerfile and logging.

Config Options

There are a number of configuration options available, which can either be set directly in the airflow.cfg file under an “aws_ecs_executor” section or via environment variables using the AIRFLOW__AWS_ECS_EXECUTOR__<OPTION_NAME> format, for example AIRFLOW__AWS_ECS_EXECUTOR__CONTAINER_NAME = "myEcsContainer". For more information on how to set these options, see Setting Configuration Options

Note

Configuration options must be consistent across all the hosts/environments running the Airflow components (Scheduler, Webserver, ECS Task containers, etc). See here for more details on setting configurations.

In the case of conflicts, the order of precedence from lowest to highest is:

  1. Load default values for options which have defaults.

  2. Load any values explicitly provided through airflow.cfg or environment variables. These are checked with Airflow’s config precedence.

  3. Load any values provided in the RUN_TASK_KWARGS option if one is provided.

Required config options:

  • CLUSTER - Name of the Amazon ECS Cluster. Required.

  • CONTAINER_NAME - Name of the container that will be used to execute Airflow tasks via the ECS executor. The container should be specified in the ECS Task Definition. Required.

  • REGION - The name of the AWS Region where Amazon ECS is configured. Required.

Optional config options:

  • ASSIGN_PUBLIC_IP - Whether to assign a public IP address to the containers launched by the ECS executor. Defaults to “False”.

  • CONN_ID - The Airflow connection (i.e. credentials) used by the ECS executor to make API calls to AWS ECS. Defaults to “aws_default”.

  • LAUNCH_TYPE - Launch type can either be ‘FARGATE’ OR ‘EC2’. Defaults to “FARGATE”.

  • PLATFORM_VERSION - The platform version the ECS task uses if the FARGATE launch type is used. Defaults to “LATEST”.

  • RUN_TASK_KWARGS - A JSON string containing arguments to provide the ECS run_task API.

  • SECURITY_GROUPS - Up to 5 comma-separated security group IDs associated with the ECS task. Defaults to the VPC default.

  • SUBNETS - Up to 16 comma-separated subnet IDs associated with the ECS task or service. Defaults to the VPC default.

  • TASK_DEFINITION - The family and revision (family:revision) or full ARN of the ECS task definition to run. Defaults to the latest ACTIVE revision.

  • MAX_RUN_TASK_ATTEMPTS - The maximum number of times the Ecs Executor should attempt to run a task. This refers to instances where the task fails to start (i.e. ECS API failures, container failures etc.)

  • CHECK_HEALTH_ON_STARTUP - Whether or not to check the ECS Executor health on startup

For a more detailed description of available options, including type hints and examples, see the config_templates folder in the Amazon provider package.

Dockerfile for ECS Executor

An example Dockerfile can be found here, it creates an image that can be used on an ECS container to run Airflow tasks using the AWS ECS Executor in Apache Airflow. The image supports AWS CLI/API integration, allowing you to interact with AWS services within your Airflow environment. It also includes options to load DAGs (Directed Acyclic Graphs) from either an S3 bucket or a local folder.

Base Image

The Docker image is built upon the apache/airflow:latest image. See here for more information about the image.

Important note: The Airflow and python versions in this image must align with the Airflow and python versions on the host/container which is running the Airflow scheduler process (which in turn runs the executor). The Airflow version of the image can be verified by running the container locally with the following command:

docker run <image_name> version

Similarly, the python version of the image can be verified the following command:

docker run <image_name> python --version

Ensure that these versions match the versions on the host/container which is running the Airflow scheduler process (and thus, the ECS executor.) Apache Airflow images with specific python versions can be downloaded from the Dockerhub registry, and filtering tags by the python version. For example, the tag latest-python3.8 specifies that the image will have python 3.8 installed.

Prerequisites

Docker must be installed on your system. Instructions for installing Docker can be found here.

AWS Credentials

The AWS CLI is installed within the container, and there are multiple ways to pass AWS authentication information to the container. This guide will cover 2 methods.

The most secure method is to use IAM roles. When creating an ECS Task Definition, you are able to select a Task Role and a Task Execution Role. The Task Execution Role is the role that is used by the container agent to make AWS API requests on your behalf. For the purposes of the ECS Executor, this role needs to have at least the AmazonECSTaskExecutionRolePolicy as well as the CloudWatchLogsFullAccess (or CloudWatchLogsFullAccessV2) policies. The Task Role is the role that is used by the containers to make AWS API requests. This role needs to have permissions based on the tasks that are described in the DAG being run. If you are loading DAGs via an S3 bucket, this role needs to have permission to read the S3 bucket.

To create a new Task Role or Task Execution Role, follow the steps below:

  1. Navigate to the IAM page on the AWS console, and from the left hand tab, under Access Management, select Roles.

  2. On the Roles page, click Create role on the top right hand corner.

  3. Under Trusted entity type, select AWS Service.

  4. Select Elastic Container Service from the drop down under Use case, and Elastic Container Service Task as the specific use case. Click Next.

  5. In the Permissions page, select the permissions the role will need, depending on whether the role is a Task Role or a Task Execution Role. Click Next after selecting all the required permissions.

  6. Enter a name for the new role, and an optional description. Review the Trusted Entities, and the permissions for the role. Add any tags as necessary, and click Create role.

When creating the Task Definition for the ECS cluster (see the setup guide for more details), select the appropriate newly created Task Role and Task Execution role for the Task Definition.

The second method is to use the build-time arguments (aws_access_key_id, aws_secret_access_key, aws_default_region, and aws_session_token).

Note: This method is not recommended for use in production environments, because user credentials are stored in the container, which may be a security vulnerability.

To pass AWS authentication information using these arguments, use the --build-arg option during the Docker build process. For example:

docker build -t my-airflow-image \
 --build-arg aws_access_key_id=YOUR_ACCESS_KEY \
 --build-arg aws_secret_access_key=YOUR_SECRET_KEY \
 --build-arg aws_default_region=YOUR_DEFAULT_REGION \
 --build-arg aws_session_token=YOUR_SESSION_TOKEN .

Replace YOUR_ACCESS_KEY, YOUR_SECRET_KEY, YOUR_SESSION_TOKEN, and YOUR_DEFAULT_REGION with valid AWS credentials.

Alternatively, you can authenticate to AWS using the ~/.aws folder. See instructions on how to generate this folder here. Uncomment the line in the Dockerfile to copy the ./.aws folder from your host machine to the container’s /home/airflow/.aws directory. Keep in mind the Docker build context when copying the .aws folder to the container.

Loading DAGs

There are many ways to load DAGs on the ECS container. This Dockerfile is preconfigured with two possible ways: copying from a local folder, or downloading from an S3 bucket. Other methods of loading DAGs are possible as well.

From S3 Bucket

To load DAGs from an S3 bucket, uncomment the entrypoint line in the Dockerfile to synchronize the DAGs from the specified S3 bucket to the /opt/airflow/dags directory inside the container. You can optionally provide container_dag_path as a build argument if you want to store the DAGs in a directory other than /opt/airflow/dags.

Add --build-arg s3_url=YOUR_S3_URL in the docker build command. Replace YOUR_S3_URL with the URL of your S3 bucket. Make sure you have the appropriate permissions to read from the bucket.

Note that the following command is also passing in AWS credentials as build arguments.

docker build -t my-airflow-image \
 --build-arg aws_access_key_id=YOUR_ACCESS_KEY \
 --build-arg aws_secret_access_key=YOUR_SECRET_KEY \
 --build-arg aws_default_region=YOUR_DEFAULT_REGION \
 --build-arg aws_session_token=YOUR_SESSION_TOKEN \
 --build-arg s3_url=YOUR_S3_URL .

From Local Folder

To load DAGs from a local folder, place your DAG files in a folder within the docker build context on your host machine, and provide the location of the folder using the host_dag_path build argument. By default, the DAGs will be copied to /opt/airflow/dags, but this can be changed by passing the container_dag_path build-time argument during the Docker build process:

docker build -t my-airflow-image --build-arg host_dag_path=./dags_on_host --build-arg container_dag_path=/path/on/container .

If choosing to load DAGs onto a different path than /opt/airflow/dags, then the new path will need to be updated in the Airflow config.

Installing Python Dependencies

This Dockerfile supports installing Python dependencies via pip from a requirements.txt file. Place your requirements.txt file in the same directory as the Dockerfile. If it is in a different location, it can be specified using the requirements_path build-argument. Keep in mind the Docker context when copying the requirements.txt file. Uncomment the two appropriate lines in the Dockerfile that copy the requirements.txt file to the container, and run pip install to install the dependencies on the container.

Building Image for ECS Executor

Detailed instructions on how to use the Docker image, that you have created via this readme, with the ECS Executor can be found here.

Logging

Airflow tasks executed via this executor run in ECS containers within the configured VPC. This means that logs are not directly accessible to the Airflow Webserver and when containers are stopped, after task completion, the logs would be permanently lost.

Remote logging should be employed when using the ECS executor to persist your Airflow Task logs and make them viewable from the Airflow Webserver.

Configuring Remote Logging

There are many ways to configure remote logging and several supported destinations. A general overview of Airflow Task logging can be found here. Instructions for configuring S3 remote logging can be found here and Cloudwatch remote logging here. Some important things to point out for remote logging in the context of the ECS executor:

  • The configuration options for Airflow remote logging should be configured on all hosts and containers running Airflow. For example the Webserver requires this config so that it can fetch logs from the remote location and the ECS container requires the config so that it can upload the logs to the remote location. See here to read more about how to set Airflow configuration via config file or environment variable exports.

  • Adding the Airflow remote logging config to the container can be done in many ways. Some examples include, but are not limited to:

    • Exported as environment variables directly in the Dockerfile (see the Dockerfile section above)

    • Updating the airflow.cfg file or copy/mounting/downloading a custom airflow.cfg in the Dockerfile.

    • Added in the ECS Task Definition in plain text or via Secrets/System Manager

    • Or, using ECS Task Environment Files

  • You must have credentials configured within the container to be able to interact with the remote service for your logs (e.g. S3, CloudWatch Logs, etc). This can be done in many ways. Some examples include, but are not limited to:

    • Export credentials into the Dockerfile directly (see the Dockerfile section above)

    • Configure an Airflow Connection and provide this as the remote logging conn id (exported into the container by any of the means listed above or your preferred method). Airflow will then use these credentials specifically for interacting with your chosen remote logging destination.

Note

Configuration options must be consistent across all the hosts/environments running the Airflow components (Scheduler, Webserver, ECS Task containers, etc). See here for more details on setting configurations.

ECS Task Logging

ECS can be configured to use the awslogs log driver to send log information to CloudWatch Logs for the ECS Tasks themselves. These logs will include the Airflow Task Operator logging and any other logging that occurs throughout the life of the process running in the container (in this case the Airflow CLI command airflow tasks run ...). This can be helpful for debugging issues with remote logging or while testing remote logging configuration. Information on enabling this logging can be found here.

Note: These logs will NOT be viewable from the Airflow Webserver UI.

Performance and Tuning

While the ECS executor adds about 50-60 seconds of latency to each Airflow task execution, due to container startup time, it allows for a higher degree of parallelism and isolation. We have tested this executor with over 1,000 tasks scheduled in parallel and observed that up to 500 tasks could be run in parallel simultaneously. The limit of 500 tasks is in accordance with ECS Service Quotas.

When running this executor, and Airflow generally, at a large scale there are some configuration options to take into consideration. Many of the below configurations will either limit how many tasks can run concurrently or the performance of the scheduler.

Setting up an ECS Executor for Apache Airflow

There are 3 steps involved in getting an ECS Executor to work in Apache Airflow:

  1. Creating a database that Airflow and the tasks running in ECS can connect to.

  2. Creating and configuring an ECS Cluster that can run tasks from Airflow.

  3. Configuring Airflow to use the ECS Executor and the database.

There are different options for selecting a database backend. See here for more information about the different options supported by Airflow. The following guide will explain how to set up a PostgreSQL RDS Instance on AWS. The guide will also cover setting up an ECS cluster. The ECS Executor supports various launch types, but this guide will explain how to set up an ECS Fargate cluster.

Setting up an RDS DB Instance for ECS Executors

Create the RDS DB Instance

  1. Log in to your AWS Management Console and navigate to the RDS service.

  2. Click “Create database” to start creating a new RDS instance.

  3. Choose the “Standard create” option, and select PostreSQL.

  4. Select the appropriate template, availability and durability.

    • NOTE: At the time of this writing, the “Multi-AZ DB Cluster” option does not support setting the database name, which is a required step below.

  5. Set the DB Instance name, the username and password.

  6. Choose the instance configuration, and storage parameters.

  7. In the Connectivity section, select Don’t connect to an EC2 compute resource

  8. Select or create a VPC and subnet, and allow public access to the DB. Select or create security group and select the Availability Zone.

  9. Open the Additional Configuration tab and set the database name to airflow_db.

  10. Select other settings as required, and create the database by clicking Create database.

Test Connectivity

In order to be able to connect to the new RDS instance, you need to allow inbound traffic to the database from your IP address.

  1. Under the “Security” heading in the “Connectivity & security” tab of the RDS instance, find the link to the VPC security group for your new RDS DB instance.

  2. Create an inbound rule that allows traffic from your IP address(es) on TCP port 5432 (PostgreSQL).

  3. Confirm that you can connect to the DB after modifying the security group. This will require having psql installed. Instructions for installing psql can be found here.

NOTE: Be sure that the status of your DB is Available before testing connectivity

psql -h <endpoint> -p 5432 -U <username> <db_name>

The endpoint can be found on the “Connectivity and Security” tab, the username (and password) are the credentials used when creating the database.

The db_name should be airflow_db (unless a different one was used when creating the database.)

You will be prompted to enter the password if the connection is successful.

Creating an ECS Cluster with Fargate, and Task Definitions

In order to create a Task Definition for the ECS Cluster that will work with Apache Airflow, you will need a Docker image that is properly configured. See the Dockerfile section for instructions on how to do that.

Once the image is built, it needs to be put in a repository where it can be pulled by ECS. There are multiple ways to accomplish this. This guide will go over doing this using Amazon Elastic Container Registry (ECR).

Create an ECR Repository

  1. Log in to your AWS Management Console and navigate to the ECR service.

  2. Click Create repository.

  3. Name the repository and fill out other information as required.

  4. Click Create Repository.

  5. Once the repository has been created, click on the repository. Click on the “View push commands” button on the top right.

  6. Follow the instructions to push the Docker image, replacing image names as appropriate. Ensure the image is uploaded by refreshing the page once the image is pushed.

Create ECS Cluster

  1. Log in to your AWS Management Console and navigate to the Amazon Elastic Container Service.

  2. Click “Clusters” then click “Create Cluster”.

  3. Make sure that AWS Fargate (Serverless) is selected under Infrastructure.

  4. Select other options as required and click Create to create the cluster.

Create Task Definition

  1. Click on Task Definitions on the left hand bar, and click Create new task definition.

  2. Choose the Task Definition Family name. Select AWS Fargate for the Launch Type.

  3. Select or create the Task Role and Task Execution Role, and ensure the roles have the required permissions to accomplish their respective tasks. You can choose to create a new Task Execution role that will have the basic minimum permissions in order for the task to run.

  4. Select a name for the container, and use the image URI of the image that was pushed in the previous section. Make sure the role being used has the required permissions to pull the image.

  5. Add the following environment variables to the container:

  • AIRFLOW__DATABASE__SQL_ALCHEMY_CONN, with the value being the PostgreSQL connection string in the following format using the values set during the Database section above:

postgresql+psycopg2://<username>:<password>@<endpoint>/<database_name>

  • AIRFLOW__ECS_EXECUTOR__SECURITY_GROUPS, with the value being a comma separated list of security group IDs associated with the VPC used for the RDS instance.

  • AIRFLOW__ECS_EXECUTOR__SUBNETS, with the value being a comma separated list of subnet IDs of the subnets associated with the RDS instance.

  1. Add other configuration as necessary for Airflow generally (see here), the ECS executor (see here) or for remote logging (see here). Note that any configuration changes should be made across the entire Airflow environment to keep configuration consistent.

  2. Click Create.

Allow ECS Containers to Access RDS Database

As a final step, access to the database must be configured for the ECS containers. Many different networking configurations are possible, but one possible approach is:

  1. Log in to your AWS Management Console and navigate to the VPC Dashboard.

  2. On the left hand, under the Security heading, click Security groups.

  3. Select the security group associated with your RDS instance, and click Edit inbound rules.

  4. Add a new rule that allows PostgreSQL type traffic to the CIDR of the subnet(s) associated with the DB.

Configure Airflow

To configure Airflow to utilize the ECS Executor and leverage the resources we’ve set up, create a script (e.g., ecs_executor_config.sh) with the following contents:

export AIRFLOW**CORE**EXECUTOR='airflow.providers.amazon.aws.executors.ecs.ecs_executor.AwsEcsExecutor'

export AIRFLOW**DATABASE**SQL*ALCHEMY*CONN=<postgres-connection-string>

export AIRFLOW__AWS_ECS_EXECUTOR__REGION=<executor-region>

export AIRFLOW__AWS_ECS_EXECUTOR__CLUSTER=<ecs-cluster-name>

export AIRFLOW__AWS_ECS_EXECUTOR__CONTAINER_NAME=<ecs-container-name>

export AIRFLOW__AWS_ECS_EXECUTOR__TASK_DEFINITION=<task-definition-name>

export AIRFLOW__AWS_ECS_EXECUTOR__LAUNCH_TYPE='FARGATE'

export AIRFLOW__AWS_ECS_EXECUTOR__PLATFORM_VERSION='LATEST'

export AIRFLOW__AWS_ECS_EXECUTOR__ASSIGN_PUBLIC_IP='True'

export AIRFLOW__AWS_ECS_EXECUTOR__SECURITY_GROUPS=<security-group-id-for-rds>

export AIRFLOW__AWS_ECS_EXECUTOR__SUBNETS=<subnet-id-for-rds>

This script should be run on the host(s) running the Airflow Scheduler and Webserver, before those processes are started.

The script sets environment variables that configure Airflow to use the ECS Executor and provide necessary information for task execution. Any other configuration changes made (such as for remote logging) should be added to this example script to keep configuration consistent across the Airflow environment.

Initialize the Airflow DB

The Airflow DB needs to be initialized before it can be used and a user needs to be added for you to log in. The below command adds an admin user (the command will also initialize the DB if it hasn’t been already):

airflow users create --username admin --password admin --firstname <your first name> --lastname <your last name> --email <your email> --role Admin

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