# Restart individual containers in Amazon ECS tasks with container restart policies
<a name="container-restart-policy"></a>

You can enable a restart policy for each essential and non-essential container defined in your task definition, to overcome transient failures faster and maintain task availability. When you enable a restart policy for a container, Amazon ECS can restart the container if it exits, without needing to replace the task.

Restart policies are not enabled for containers by default. When you enable a restart policy for a container, you can specify exit codes that the container will not be restarted on. These can be exit codes that indicate success, like exit code `0`, that don't require a restart. You can also specify how long a container must run succesfully before a restart can be attempted. For more information about these parameters, see [Restart policy](task_definition_parameters.md#container_definition_restart_policy). For an example task definition that specifies these values, see [Specifying a container restart policy in an Amazon ECS task definition](container-restart-policy-example.md).

You can use the Amazon ECS task metadata endpoint or CloudWatch Container Insights to monitor the number of times a container has restarted. For more information about the task metadata endpoint, see [Amazon ECS task metadata endpoint version 4](task-metadata-endpoint-v4.md) and [Amazon ECS task metadata endpoint version 4 for tasks on Fargate](task-metadata-endpoint-v4-fargate.md). For more information about Container Insights metrics for Amazon ECS, see [Amazon ECS Container Insights metrics](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Container-Insights-metrics-ECS.html) in the *Amazon CloudWatch User Guide*.

Container restart policies are supported by tasks hosted on Fargate, Amazon EC2 instances, and external instances using Amazon ECS Anywhere.

## Considerations
<a name="container-restart-policy-considerations"></a>

Consider the following before enabling a restart policy for your container:
+ Restart policies aren't supported for Windows containers on Fargate.
+ For tasks hosted on Amazon EC2 instances, this feature requires version `1.86.0` or later of the container agent. However, we recommend using the latest container agent version. For information about how to check your agent version and update to the latest version, see [Updating the Amazon ECS container agent](ecs-agent-update.md).
+ If you're using EC2 with the `bridge` network mode, the `FLUENT_HOST` environment variable in your application container can become inaccurate after a restart of the FireLens log router container (the container with the `firelensConfiguration` object in its container definition). This is because `FLUENT_HOST` is a dynamic IP address and can change after a restart. Logging directly from the application container to the `FLUENT_HOST` IP address can start failing after the address changes. For more information about `FLUENT_HOST`, see [Configuring Amazon ECS logs for high throughput](firelens-docker-buffer-limit.md).
+ The Amazon ECS agent handles the container restart policies. If for some unexpected reason the Amazon ECS agent fails or is no longer running, the container won't be restarted.
+  The restart attempt period defined in your policy determines the period of time (in seconds) that the container must run for before Amazon ECS restarts a container.

# Specifying a container restart policy in an Amazon ECS task definition
<a name="container-restart-policy-example"></a>

To specify a restart policy for a container in a task definition, within the container definition, specify the `restartPolicy` object. For more information about the `restartPolicy` object, see [Restart policy](task_definition_parameters.md#container_definition_restart_policy).

The following is a task definition using the Linux containers on Fargate that sets up a web server. The container definition includes the `restartPolicy` object, with `enabled` set to true to enable a restart policy for the container. The container must run for 180 seconds before it can be restarted and will not be restarted if it exits with the exit code `0`, which indicates success.

```
{
  "containerDefinitions": [
    {
      "command": [
        "/bin/sh -c \"echo '<html> <head> <title>Amazon ECS Sample App</title> <style>body {margin-top: 40px; background-color: #333;} </style> </head><body> <div style=color:white;text-align:center> <h1>Amazon ECS Sample App</h1> <h2>Congratulations!</h2> <p>Your application is now running on a container in Amazon ECS.</p> </div></body></html>' >  /usr/local/apache2/htdocs/index.html && httpd-foreground\""
      ],
      "entryPoint": ["sh", "-c"],
      "essential": true,
      "image": "public.ecr.aws/docker/library/httpd:2.4",
      "logConfiguration": {
        "logDriver": "awslogs",
        "options": {
          "awslogs-group": "/ecs/fargate-task-definition",
          "awslogs-region": "us-east-1",
          "awslogs-stream-prefix": "ecs"
        }
      },
      "name": "sample-fargate-app",
      "portMappings": [
        {
          "containerPort": 80,
          "hostPort": 80,
          "protocol": "tcp"
        }
      ],
      "restartPolicy": {
        "enabled": true,
        "ignoredExitCodes": [0],
        "restartAttemptPeriod": 180
      }
    }
  ],
  "cpu": "256",
  "executionRoleArn": "arn:aws:iam::012345678910:role/ecsTaskExecutionRole",
  "family": "fargate-task-definition",
  "memory": "512",
  "networkMode": "awsvpc",
  "runtimePlatform": {
    "operatingSystemFamily": "LINUX"
  },
  "requiresCompatibilities": ["FARGATE"]
}
```

After you have registered a task definition with the `restartPolicy` object in a container definition, you can run a task or create a service with that task definition. For more information, see [Running an application as an Amazon ECS task](standalone-task-create.md) and [Creating an Amazon ECS rolling update deployment](create-service-console-v2.md).