Running a script when you launch an Amazon ECS Linux container instance - Amazon Elastic Container Service

Running a script when you launch an Amazon ECS Linux container instance

You might need to run a specific container on every container instance to deal with operations or security concerns such as monitoring, security, metrics, service discovery, or logging.

To do this, you can configure your container instances to call the docker run command with the user data script at launch, or in some init system such as Upstart or systemd. While this method works, it has some disadvantages because Amazon ECS has no knowledge of the container and cannot monitor the CPU, memory, ports, or any other resources used. To ensure that Amazon ECS can properly account for all task resources, create a task definition for the container to run on your container instances. Then, use Amazon ECS to place the task at launch time with Amazon EC2 user data.

The Amazon EC2 user data script in the following procedure uses the Amazon ECS introspection API to identify the container instance. Then, it uses the AWS CLI and the start-task command to run a specified task on itself during startup.

To start a task at container instance launch time

  1. Modify your ecsInstanceRole IAM role to add permissions for the StartTask API operation. For more information, see Update permissions for a role in the AWS Identity and Access Management User Guide.

  2. Launch one or more container instances using the Amazon ECS-optimized Amazon Linux 2 AMI. Launch new container instances and use the following example script in the EC2 User data. Replace your_cluster_name with the cluster for the container instance to register into and my_task_def with the task definition to run on the instance at launch.

    For more information, see Launching an Amazon ECS Linux container instance.

    Note

    The MIME multi-part content below uses a shell script to set configuration values and install packages. It also uses a systemd job to start the task after the ecs service is running and the introspection API is available.

    Content-Type: multipart/mixed; boundary="==BOUNDARY=="
MIME-Version: 1.0

--==BOUNDARY==
Content-Type: text/x-shellscript; charset="us-ascii"

#!/bin/bash
# Specify the cluster that the container instance should register into
cluster=your_cluster_name

# Write the cluster configuration variable to the ecs.config file
# (add any other configuration variables here also)
echo ECS_CLUSTER=$cluster >> /etc/ecs/ecs.config

START_TASK_SCRIPT_FILE="/etc/ecs/ecs-start-task.sh"
cat <<- 'EOF' > ${START_TASK_SCRIPT_FILE}
	exec 2>>/var/log/ecs/ecs-start-task.log
	set -x
	
	# Install prerequisite tools
	yum install -y jq aws-cli
	
	# Wait for the ECS service to be responsive
	until curl -s http://localhost:51678/v1/metadata
	do
		sleep 1
	done

	# Grab the container instance ARN and AWS Region from instance metadata
	instance_arn=$(curl -s http://localhost:51678/v1/metadata | jq -r '. | .ContainerInstanceArn' | awk -F/ '{print $NF}' )
	cluster=$(curl -s http://localhost:51678/v1/metadata | jq -r '. | .Cluster' | awk -F/ '{print $NF}' )
	region=$(curl -s http://localhost:51678/v1/metadata | jq -r '. | .ContainerInstanceArn' | awk -F: '{print $4}')

	# Specify the task definition to run at launch
	task_definition=my_task_def

	# Run the AWS CLI start-task command to start your task on this container instance
	aws ecs start-task --cluster $cluster --task-definition $task_definition --container-instances $instance_arn --started-by $instance_arn --region $region
EOF

# Write systemd unit file
UNIT="ecs-start-task.service"
cat <<- EOF > /etc/systemd/system/${UNIT}
      [Unit]
      Description=ECS Start Task
      Requires=ecs.service
      After=ecs.service
 
      [Service]
      Restart=on-failure
      RestartSec=30
      ExecStart=/usr/bin/bash ${START_TASK_SCRIPT_FILE}

      [Install]
      WantedBy=default.target
EOF

# Enable our ecs.service dependent service with `--no-block` to prevent systemd deadlock
# See https://github.com/aws/amazon-ecs-agent/issues/1707
systemctl enable --now --no-block "${UNIT}"
--==BOUNDARY==--

  3. Verify that your container instances launch into the correct cluster and that your tasks have started.

    1. Open the console at https://console.aws.amazon.com/ecs/v2.

    2. From the navigation bar, choose the Region that your cluster is in.

    3. In the navigation pane, choose Clusters and select the cluster that hosts your container instances.

    4. On the Cluster page, choose Tasks, and then choose yor tasks.

      Each container instance you launched should have your task running on it.

      If you do not see your tasks, you can log in to your container instances with SSH and check the /var/log/ecs/ecs-start-task.log file for debugging information.