Using the awslogs log driver

You can configure the containers in your tasks to send log information to CloudWatch Logs. This allows you to view the logs from the containers in your Fargate tasks.This topic helps you get started using the awslogs log driver in your task definitions.

Note

The type of information that is logged by the containers in your task depends mostly on their ENTRYPOINT command. By default, the logs that are captured show the command output that you would normally see in an interactive terminal if you ran the container locally, which are the STDOUT and STDERR I/O streams. The awslogs log driver simply passes these logs from Docker to CloudWatch Logs. For more information on how Docker logs are processed, including alternative ways to capture different file data or streams, see View logs for a container or service in the Docker documentation.

Turning on the awslogs log driver for your containers

If you are using the Fargate launch type for your tasks, all you need to do to turn on the awslogs log driver is add the required logConfiguration parameters to your task definition. For more information, see Specifying a log configuration in your task definition.

Creating a log group

The awslogs log driver can send log streams to an existing log group in CloudWatch Logs or it can create a new log group on your behalf. The AWS Management Console provides an auto-configure option which creates a log group on your behalf using the task definition family name with ecs as the prefix. Alternatively, you can manually specify your log configuration options and specify the awslogs-create-group option with a value of true which will create the log groups on your behalf.

Note

To use the awslogs-create-group option to have your log group created, your IAM policy must include the logs:CreateLogGroup permission.

The following code shows how to set the awslogs-create-group option.

{
    "containerDefinitions": [
        {
            "logConfiguration": {
                "logDriver": "awslogs",
                "options": {
                    "awslogs-group": "firelens-container",
                    "awslogs-region": "us-west-2",
                    "awslogs-create-group": "true",
                    "awslogs-stream-prefix": "firelens"
                }
            }
}

Using the auto-configuration feature to create a log group

When registering a task definition in the Amazon ECS console, you have the option to allow Amazon ECS to auto-configure your CloudWatch logs. This option creates a log group on your behalf using the task definition family name with ecs as the prefix.

To use log group auto-configuration option in the Amazon ECS console

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

2. In the left navigation pane, choose Task Definitions, Create new Task Definition.

3. Select your compatibility option and choose Next Step.

4. Choose Add container.

5. In the Storage and Logging section, for Log configuration, choose Auto-configure CloudWatch Logs.

6. Enter your awslogs log driver options. For more information, see Specifying a log configuration in your task definition.

7. Complete the rest of the task definition wizard.

Available awslogs log driver options

The awslogs log driver supports the following options in Amazon ECS task definitions. For more information, see CloudWatch Logs logging driver.

awslogs-create-group

Required: No

Specify whether you want the log group automatically created. If this option is not specified, it defaults to false.

Note

Your IAM policy must include the logs:CreateLogGroup permission before you attempt to use awslogs-create-group.

awslogs-region

Required: Yes

Specify the region to which the awslogs log driver should send your Docker logs. You can choose to send all of your logs from clusters in different regions to a single region in CloudWatch Logs so that they are all visible in one location, or you can separate them by region for more granularity. Be sure that the specified log group exists in the region that you specify with this option.

awslogs-group

Required: Yes

You must specify a log group to which the awslogs log driver sends its log streams. For more information, see Creating a log group.

awslogs-stream-prefix

Required: Yes, when using the Fargate launch type.

The awslogs-stream-prefix option allows you to associate a log stream with the specified prefix, the container name, and the ID of the Amazon ECS task to which the container belongs. If you specify a prefix with this option, then the log stream takes the following format:

prefix-name/container-name/ecs-task-id

For Amazon ECS services, you could use the service name as the prefix, which would allow you to trace log streams to the service that the container belongs to, the name of the container that sent them, and the ID of the task to which the container belongs.

awslogs-datetime-format

Required: No

This option defines a multiline start pattern in Python strftime format. A log message consists of a line that matches the pattern and any following lines that don’t match the pattern. Thus the matched line is the delimiter between log messages.

One example of a use case for using this format is for parsing output such as a stack dump, which might otherwise be logged in multiple entries. The correct pattern allows it to be captured in a single entry.

For more information, see awslogs-datetime-format.

This option always takes precedence if both awslogs-datetime-format and awslogs-multiline-pattern are configured.

Note

Multiline logging performs regular expression parsing and matching of all log messages, which may have a negative impact on logging performance.

awslogs-multiline-pattern

Required: No

This option defines a multiline start pattern using a regular expression. A log message consists of a line that matches the pattern and any following lines that don’t match the pattern. Thus the matched line is the delimiter between log messages.

For more information, see awslogs-multiline-pattern.

This option is ignored if awslogs-datetime-format is also configured.

Note

Multiline logging performs regular expression parsing and matching of all log messages. This may have a negative impact on logging performance.

mode

Required: No

Valid values: non-blocking | blocking

Default value: blocking

The delivery mode of log messages from the container to awslogs. For more information, see Configure logging drivers.

max-buffer-size

Required: No

Default value: 1m

When non-blocking mode is used, the max-buffer-size log option controls the size of the ring buffer used for intermediate message storage.

Specifying a log configuration in your task definition

Before your containers can send logs to CloudWatch, you must specify the awslogs log driver for containers in your task definition. This section describes the log configuration for a container to use the awslogs log driver. For more information, see Creating a task definition using the new console.

The task definition JSON shown below has a logConfiguration object specified for each container; one for the WordPress container that sends logs to a log group called awslogs-wordpress, and one for a MySQL container that sends logs to a log group called awslogs-mysql. Both containers use the awslogs-example log stream prefix.

{
    "containerDefinitions": [
        {
            "name": "wordpress",
            "links": [
                "mysql"
            ],
            "image": "wordpress",
            "essential": true,
            "portMappings": [
                {
                    "containerPort": 80,
                    "hostPort": 80
                }
            ],
            "logConfiguration": {
                "logDriver": "awslogs",
                "options": {
                    "awslogs-group": "awslogs-wordpress",
                    "awslogs-region": "us-west-2",
                    "awslogs-stream-prefix": "awslogs-example"
                }
            },
            "memory": 500,
            "cpu": 10
        },
        {
            "environment": [
                {
                    "name": "MYSQL_ROOT_PASSWORD",
                    "value": "password"
                }
            ],
            "name": "mysql",
            "image": "mysql",
            "cpu": 10,
            "memory": 500,
            "essential": true,
            "logConfiguration": {
                "logDriver": "awslogs",
                "options": {
                    "awslogs-group": "awslogs-mysql",
                    "awslogs-region": "us-west-2",
                    "awslogs-stream-prefix": "awslogs-example"
                }
            }
        }
    ],
    "family": "awslogs-example"
}

In the Amazon ECS console, the log configuration for the wordpress container is specified as shown in the image below.

Viewing awslogs container logs in CloudWatch Logs

After your Fargate tasks that use the awslogs log driver have launched, your configured containers should be sending their log data to CloudWatch Logs. You can view and search these logs in the console.

To view your CloudWatch Logs data for a container from the Amazon ECS console

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

2. On the Clusters page, select the cluster that contains the task to view.

3. On the Cluster: cluster_name page, choose Tasks and select the task to view.

4. On the Task: task_id page, expand the container view by choosing the arrow to the left of the container name.

5. In the Log Configuration section, choose View logs in CloudWatch, which opens the associated log stream in the CloudWatch console.

   

To view your CloudWatch Logs data in the CloudWatch console

1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

2. In the left navigation pane, choose Logs.

3. Select a log group to view. You should see the log groups that you created in Creating a log group.

   

4. Choose a log stream to view.