Configuring Amazon ECS logs for high throughput

When you create a task definition, you can specify the number of log lines that are buffered in memory by specifying the value in the log-driver-buffer-limit. For more information, see Fluentd logging driver in the Docker documentation.

Use this option when there's high throughput, because Docker might run out of buffer memory and discard buffer messages, so it can add new messages.

Consider the following when using FireLens for Amazon ECS with the buffer limit option:

• This option is supported on EC2 and Fargate type with platform version 1.4.0 or later.

• The option is only valid when logDriver is set to awsfirelens.

• The default buffer limit is 1048576 log lines.

• The buffer limit must be greater than or equal to 0 and less than 536870912 log lines.

• The maximum amount of memory used for this buffer is the product of the size of each log line and the size of the buffer. For example, if the application’s log lines are on average 2 KiB, a buffer limit of 4096 would use at most 8 MiB. The total amount of memory allocated at the task level should be greater than the amount of memory that's allocated for all the containers in addition to the log driver memory buffer.

When the awsfirelens log driver is specified in a task definition, the Amazon ECS container agent injects the following environment variables into the container:

FLUENT_HOST

The IP address that's assigned to the FireLens container.

Note

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 restarting individual containers, see Restart individual containers in Amazon ECS tasks with container restart policies.

FLUENT_PORT

The port that the Fluent Forward protocol is listening on.

You can use the FLUENT_HOST and FLUENT_PORT environment variables to log directly to the log router from code instead of going through stdout. For more information, see fluent-logger-golang on GitHub.

The following shows the syntax for specifying the log-driver-buffer-limit. Replace my_service_ with the name of your service:

{
    "containerDefinitions": [
        {
            "name": "my_service_log_router",
            "image": "public.ecr.aws/aws-observability/aws-for-fluent-bit:stable",
            "cpu": 0,
            "memoryReservation": 51,
            "portMappings": [],
            "essential": true,
            "environment": [],
            "mountPoints": [],
            "volumesFrom": [],
            "logConfiguration": {
                "logDriver": "awslogs",
                "options": {
                    "awslogs-group": "/ecs/ecs-aws-firelens-sidecar-container",
                    "mode": "non-blocking",
                    "awslogs-create-group": "true",
                    "max-buffer-size": "25m",
                    "awslogs-region": "us-east-1",
                    "awslogs-stream-prefix": "firelens"
                },
                "secretOptions": []
            },
            "systemControls": [],
            "firelensConfiguration": {
                "type": "fluentbit"
            }
        },
        {
            "essential": true,
            "image": "public.ecr.aws/docker/library/httpd:latest",
            "name": "app",
            "logConfiguration": {
                "logDriver": "awsfirelens",
                "options": {
                    "Name": "firehose",
                    "region": "us-west-2",
                    "delivery_stream": "my-stream",
                    "log-driver-buffer-limit": "51200"
                }
            },
            "dependsOn": [
                {
                    "containerName": "log_router",
                    "condition": "START"
                }
            ],
            "memoryReservation": 100
        }
    ]
}