Using the awslogs log driver
You can configure the containers in your tasks to send log information to CloudWatch Logs.
If you're using the Fargate launch type for your tasks,
you can view the logs from your containers. If you're using the EC2 launch
type, you can view different logs from your containers in one convenient location, and
it prevents your container logs from taking up disk space on your container instances.
This topic goes over how you can 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 typically might 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 about how Docker logs are processed, including alternative
ways to capture different file data or streams, see View logs for a container
or service
To send system logs from your Amazon ECS container instances to CloudWatch Logs, see Monitoring Log Files and CloudWatch Logs quotas in the Amazon CloudWatch Logs User Guide.
Turning on the awslogs log driver for your containers
If you're using the Fargate launch type for your tasks, you need to add
the required logConfiguration
parameters to your task definition to turn on
the awslogs
log driver. For more information, see Specifying a log configuration in your task
definition.
If you're using the EC2 launch type for your tasks and
want to turn on the awslogs
log driver, your Amazon ECS container instances
require at least version 1.9.0 of the container agent. For
information about how to check your agent version and updating to the latest version,
see Updating the Amazon ECS container agent.
Note
If you aren't using the Amazon ECS optimized AMI (with at least version 1.9.0-1 of
the ecs-init
package) for your container instances, you also need to
specify that the awslogs
logging driver is available on the container
instance when you start the agent by using the following environment variable in
your docker run statement or environment variable file. For more
information, see Installing the Amazon ECS container agent.
ECS_AVAILABLE_LOGGING_DRIVERS=["json-file","
awslogs
"]
Your Amazon ECS container instances also require
logs:CreateLogStream
and logs:PutLogEvents
permission on
the IAM role that you can launch your container instances with. If you created your
Amazon ECS container instance role before awslogs
log driver support was enabled
in Amazon ECS, you might need to add this permission. The ecsTaskExecutionRole
is used when it's assigned to the task and likely contains the correct permissions. For
information about the task execution role, see Amazon ECS task execution IAM role. If your container instances use the
managed IAM policy for container instances, your container instances likely have the
correct permissions. For information about the managed IAM policy for container
instances, see Amazon ECS container instance IAM role.
Creating a log group
The awslogs
log driver can send log streams to an existing log group in
CloudWatch Logs or 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 creates the log groups on your behalf.
Note
To use the awslogs-create-group
option to have your log group
created, your task execution IAM role policy or EC2 instance role 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 you register a task definition,in the Amazon ECS console, you can allow Amazon ECS to
auto-configure your CloudWatch logs. Doing this causes a log group to be created on your
behalf using the task definition family name with ecs
as the prefix.
For more information, see Creating a task definition using the
console.
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 to be created automatically. If this option isn't specified, it defaults to
false
.Note
Your IAM policy must include the
logs:CreateLogGroup
permission before you attempt to useawslogs-create-group
. awslogs-region
-
Required: Yes
Specify the AWS Region that the
awslogs
log driver is to send your Docker logs to. You can choose to send all of your logs from clusters in different Regions to a single region in CloudWatch Logs. This is so that they're all visible in one location. Otherwise, you can separate them by Region for more granularity. Make sure that the specified log group exists in the Region that you specify with this option. awslogs-group
-
Required: Yes
Make sure to specify a log group that the
awslogs
log driver sends its log streams to. For more information, see Creating a log group. awslogs-stream-prefix
-
Required: Yes, when using the Fargate launch type. Optional for the EC2 launch type, required for the Fargate launch type.
Use the
awslogs-stream-prefix
option to associate a log stream with the specified prefix, the container name, and the ID of the Amazon ECS task that the container belongs to. If you specify a prefix with this option, then the log stream takes the following format.prefix-name
/container-name
/ecs-task-id
If you don't specify a prefix with this option, then the log stream is named after the container ID that's assigned by the Docker daemon on the container instance. Because it's difficult to trace logs back to the container that sent them with just the Docker container ID (which is only available on the container instance), we recommend that you specify a prefix with this option.
For Amazon ECS services, you can use the service name as the prefix. Doing so, you can 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 that the container belongs to.
You must specify a stream-prefix for your logs to have your logs appear in the Log pane when using the Amazon ECS console.
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. 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
. You cannot configure both the
awslogs-datetime-format
andawslogs-multiline-pattern
options.Note
Multiline logging performs regular expression parsing and matching of all log messages. This might have a negative impact on logging performance.
awslogs-multiline-pattern
-
Required: No
This option defines a multiline start pattern that uses a regular expression. A log message consists of a line that matches the pattern and any following lines that don’t match the pattern. 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.You cannot configure both the
awslogs-datetime-format
andawslogs-multiline-pattern
options.Note
Multiline logging performs regular expression parsing and matching of all log messages. This might have a negative impact on logging performance.
mode
-
Required: No
Valid values:
non-blocking
|blocking
Default value:
blocking
This option defines the delivery mode of log messages from the container to CloudWatch Logs. The delivery mode you choose affects application availability when the flow of logs from container to CloudWatch is interrupted.
If you use the default
blocking
mode and the flow of logs to CloudWatch is interrupted, calls from container code to write to thestdout
andstderr
streams will block. The logging thread of the application will block as a result. This may cause the application to become unresponsive and lead to container healthcheck failure.If you use the
non-blocking
mode, the container's logs are instead stored in an in-memory intermediate buffer configured with themax-buffer-size
option. This prevents the application from becoming unresponsive when logs cannot be sent to CloudWatch. We recommendusing this mode if you want to ensure service availability and are okay with some log loss. max-buffer-size
-
Required: No
Default value:
1m
When
non-blocking
mode is used, themax-buffer-size
log option controls the size of the buffer that's used for intermediate message storage. Make sure to specify an adequate buffer size based on your application. When the buffer fills up, further logs cannot be stored. Logs that cannot be stored are lost.
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
console.
The task definition JSON that follows has a logConfiguration
object
specified for each container. One is for the WordPress container that sends logs to a
log group called awslogs-wordpress
. The other is for a MySQL container that
sends logs to a log group that's 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-create-group": "true", "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-create-group": "true", "awslogs-group": "awslogs-mysql
", "awslogs-region": "us-west-2
", "awslogs-stream-prefix": "awslogs-example
", "mode": "non-blocking", "max-buffer-size": "25m" } } } ], "family": "awslogs-example" }
After you have registered a task definition with the
awslogs
log driver in a container definition log configuration, you can
run a task or create a service with that task definition to start sending logs to CloudWatch Logs.
For more information, see Run an application as an Amazon ECS task and Creating a service using the console.