Using custom log routing - Amazon Elastic Container Service

Using custom log routing

You can use FireLens for Amazon ECS to use task definition parameters to route logs to an AWS service or AWS Partner Network (APN) destination for log storage and analytics. The AWS Partner Network is a global community of partners that leverages programs, expertise, and resources to build, market, and sell customer offerings. For more information see AWS Partner. FireLens works with Fluentd and Fluent Bit. We provide the AWS for Fluent Bit image or you can use your own Fluentd or Fluent Bit image.


Consider the following when using FireLens for Amazon ECS:

  • We recommend that you add my_service_ to the log container name so that you can easily distinguish container names in the console.

  • Amazon ECS adds a start container order dependency between the application containers and the FireLens container by default. When you specify a container order between the application containers and the FireLens container, then the default start container order is overridden.

  • FireLens for Amazon ECS is supported for tasks that are hosted on both AWS Fargate on Linux and Amazon EC2 on Linux. Windows containers don't support FireLens.

    For information about how to configure centralized logging for Windows containers, see Centralized logging for Windows containers on Amazon ECS using Fluent Bit.

  • FireLens for Amazon ECS is supported in AWS CloudFormation templates. For more information, see AWS::ECS::TaskDefinition FirelensConfiguration in the AWS CloudFormation User Guide

  • FireLens listens on port 24224, so to ensure that the FireLens log router isn't reachable outside of the task, you must not allow inbound traffic on port 24224 in the security group your task uses. For tasks that use the awsvpc network mode, this is the security group associated with the task. For tasks using the host network mode, this is the security group that's associated with the Amazon EC2 instance hosting the task. For tasks that use the bridge network mode, don't create any port mappings that use port 24224.

  • For tasks that use the bridge network mode, the container with the FireLens configuration must start before any application containers that rely on it start. To control the start order of your containers, use dependency conditions in your task definition. For more information, see Container dependency.


    If you use dependency condition parameters in container definitions with a FireLens configuration, ensure that each container has a START or HEALTHY condition requirement.

  • By default, FireLens adds the cluster and task definition name and the Amazon Resource Name (ARN) of the cluster as metadata keys to your stdout/stderr container logs. The following is an example of the metadata format.

    "ecs_cluster": "cluster-name", "ecs_task_arn": "arn:aws:ecs:region:111122223333:task/cluster-name/f2ad7dba413f45ddb4EXAMPLE", "ecs_task_definition": "task-def-name:revision",

    If you do not want the metadata in your logs, set enable-ecs-log-metadata to false in the firelensConfiguration section of the task definition.

    "firelensConfiguration":{ "type":"fluentbit", "options":{ "enable-ecs-log-metadata":"false", "config-file-type":"file", "config-file-value":"/extra.conf" }

Required IAM permissions

To use this feature, you must create an IAM role for your tasks that provides the permissions necessary to use any AWS services that the tasks require. For example, if a container is routing logs to Firehose, the task requires permission to call the firehose:PutRecordBatch API. For more information, see Adding and Removing IAM Identity Permissions in the IAM User Guide.

The following example IAM policy adds the required permissions for routing logs to Firehose.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "firehose:PutRecordBatch" ], "Resource": [ "*" ] } ] }

The following example IAM policy adds the required permissions for routing logs to Amazon CloudWatch Logs.

{ "Version": "2012-10-17", "Statement": [{ "Effect": "Allow", "Action": [ "logs:CreateLogStream", "logs:CreateLogGroup", "logs:PutLogEvents" ], "Resource": "*" }] }

Your task may also require the Amazon ECS task execution role under the following conditions. For more information, see Amazon ECS task execution IAM role.

  • If your task is hosted on Fargate and you are pulling container images from Amazon ECR or referencing sensitive data from AWS Secrets Manager in your log configuration, then you must include the task execution IAM role.

  • If you are specifying a custom configuration file that's hosted in Amazon S3, your task execution IAM role must include the s3:GetObject permission for the configuration file and the s3:GetBucketLocation permission on the Amazon S3 bucket that the file is in. For more information, see Specifying Permissions in a Policy in the Amazon Simple Storage Service User Guide.

    The following example IAM policy adds the required permissions for retrieving a file from Amazon S3. Specify the name of your Amazon S3 bucket and configuration file name.

    { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:GetObject" ], "Resource": [ "arn:aws:s3:::examplebucket/folder_name/config_file_name" ] }, { "Effect": "Allow", "Action": [ "s3:GetBucketLocation" ], "Resource": [ "arn:aws:s3:::examplebucket" ] } ] }

Fluentd buffer limit

When you create a task definition, you can specify the number of events that are buffered in memory by specifying the value (in bytes) 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. The lost logs might make it difficult to troubleshoot. Setting the buffer limit might help to prevent this issue.

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

{ "containerDefinitions": [ { "essential": true, "image": "", "name": "my_service_log_router", "firelensConfiguration": { "type": "fluentbit" }, "logConfiguration": { "logDriver": "awslogs", "options": { "awslogs-group": "firelens-container", "awslogs-region": "us-west-2", "awslogs-create-group": "true", "awslogs-stream-prefix": "firelens" } }, "memoryReservation": 50 }, { "essential": true, "image": "httpd", "name": "app", "logConfiguration": { "logDriver": "awsfirelens", "options": { "Name": "firehose", "region": "us-west-2", "delivery_stream": "my-stream", "log-driver-buffer-limit": "2097152" } }, "dependsOn": [ { "containerName": "log_router", "condition": "START" } ], "memoryReservation": 100 } ] }

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

  • This option is supported on the Amazon EC2 launch type and the Fargate launch 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 1 MiB.

  • The valid values are 0 and 536870912 (512 MiB).

  • The total amount of memory allocated at the task level must be greater than the amount of memory that's allocated for all the containers in addition to the memory buffer limit. The total amount of buffer memory specified must be less than 536870912 (512MiB) when you don't specify the container memory and memoryReservation values. More specifically, you can have an app container with the awsfirelens log driver and the log-driver-buffer-limit option set to 300 MiB. However, you won’t be allowed to run tasks if you have more than two containers with the log-driver-buffer-limit set to 300 MiB (300 MiB * 2 > 512 MiB).

Using Fluent logger libraries or Log4j over TCP

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


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


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.