Amazon CloudWatch Logs logging driver

Table of contents

The awslogs logging driver sends container logs to Amazon CloudWatch Logs. Log entries can be retrieved through the AWS Management Console or the AWS SDKs and Command Line Tools.

Usage

To use the awslogs driver as the default logging driver, set the log-driver and log-opt keys to appropriate values in the daemon.json file, which is located in /etc/docker/ on Linux hosts or C:\ProgramData\docker\config\daemon.json on Windows Server. For more about configuring Docker using daemon.json, see daemon.json. The following example sets the log driver to awslogs and sets the awslogs-region option.

{
  "log-driver": "awslogs",
  "log-opts": {
    "awslogs-region": "us-east-1"
  }
}

Restart Docker for the changes to take effect.

You can set the logging driver for a specific container by using the --log-driver option to docker run:

$ docker run --log-driver=awslogs ...

If you are using Docker Compose, set awslogs using the following declaration example:

myservice:
  logging:
    driver: awslogs
    options:
      awslogs-region: us-east-1

Amazon CloudWatch Logs options

You can add logging options to the daemon.json to set Docker-wide defaults, or use the --log-opt NAME=VALUE flag to specify Amazon CloudWatch Logs logging driver options when starting a container.

awslogs-region

The awslogs logging driver sends your Docker logs to a specific region. Use the awslogs-region log option or the AWS_REGION environment variable to set the region. By default, if your Docker daemon is running on an EC2 instance and no region is set, the driver uses the instance's region.

$ docker run --log-driver=awslogs --log-opt awslogs-region=us-east-1 ...

awslogs-endpoint

By default, Docker uses either the awslogs-region log option or the detected region to construct the remote CloudWatch Logs API endpoint. Use the awslogs-endpoint log option to override the default endpoint with the provided endpoint.

Note

The awslogs-region log option or detected region controls the region used for signing. You may experience signature errors if the endpoint you've specified with awslogs-endpoint uses a different region.

awslogs-group

You must specify a log group for the awslogs logging driver. You can specify the log group with the awslogs-group log option:

$ docker run --log-driver=awslogs --log-opt awslogs-region=us-east-1 --log-opt awslogs-group=myLogGroup ...

awslogs-stream

To configure which log stream should be used, you can specify the awslogs-stream log option. If not specified, the container ID is used as the log stream.

Note

Log streams within a given log group should only be used by one container at a time. Using the same log stream for multiple containers concurrently can cause reduced logging performance.

awslogs-create-group

Log driver returns an error by default if the log group doesn't exist. However, you can set the awslogs-create-group to true to automatically create the log group as needed. The awslogs-create-group option defaults to false.

$ docker run \
    --log-driver=awslogs \
    --log-opt awslogs-region=us-east-1 \
    --log-opt awslogs-group=myLogGroup \
    --log-opt awslogs-create-group=true \
    ...

Note

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

awslogs-create-stream

By default, the log driver creates the AWS CloudWatch Logs stream used for container log persistence.

Set awslogs-create-stream to false to disable log stream creation. When disabled, the Docker daemon assumes the log stream already exists. A use case where this is beneficial is when log stream creation is handled by another process avoiding redundant AWS CloudWatch Logs API calls.

If awslogs-create-stream is set to false and the log stream does not exist, log persistence to CloudWatch fails during container runtime, resulting in Failed to put log events error messages in daemon logs.

$ docker run \
    --log-driver=awslogs \
    --log-opt awslogs-region=us-east-1 \
    --log-opt awslogs-group=myLogGroup \
    --log-opt awslogs-stream=myLogStream \
    --log-opt awslogs-create-stream=false \
    ...

awslogs-datetime-format

The awslogs-datetime-format option defines a multi-line 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.

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

Note

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

Consider the following log stream, where new log messages start with a timestamp:

[May 01, 2017 19:00:01] A message was logged
[May 01, 2017 19:00:04] Another multi-line message was logged
Some random message
with some random words
[May 01, 2017 19:01:32] Another message was logged

The format can be expressed as a strftime expression of [%b %d, %Y %H:%M:%S], and the awslogs-datetime-format value can be set to that expression:

$ docker run \
    --log-driver=awslogs \
    --log-opt awslogs-region=us-east-1 \
    --log-opt awslogs-group=myLogGroup \
    --log-opt awslogs-datetime-format='\[%b %d, %Y %H:%M:%S\]' \
    ...

This parses the logs into the following CloudWatch log events:

# First event
[May 01, 2017 19:00:01] A message was logged

# Second event
[May 01, 2017 19:00:04] Another multi-line message was logged
Some random message
with some random words

# Third event
[May 01, 2017 19:01:32] Another message was logged

The following strftime codes are supported:

Code	Meaning	Example
`%a`	Weekday abbreviated name.	Mon
`%A`	Weekday full name.	Monday
`%w`	Weekday as a decimal number where 0 is Sunday and 6 is Saturday.	0
`%d`	Day of the month as a zero-padded decimal number.	08
`%b`	Month abbreviated name.	Feb
`%B`	Month full name.	February
`%m`	Month as a zero-padded decimal number.	02
`%Y`	Year with century as a decimal number.	2008
`%y`	Year without century as a zero-padded decimal number.	08
`%H`	Hour (24-hour clock) as a zero-padded decimal number.	19
`%I`	Hour (12-hour clock) as a zero-padded decimal number.	07
`%p`	AM or PM.	AM
`%M`	Minute as a zero-padded decimal number.	57
`%S`	Second as a zero-padded decimal number.	04
`%L`	Milliseconds as a zero-padded decimal number.	.123
`%f`	Microseconds as a zero-padded decimal number.	000345
`%z`	UTC offset in the form +HHMM or -HHMM.	+1300
`%Z`	Time zone name.	PST
`%j`	Day of the year as a zero-padded decimal number.	363

awslogs-multiline-pattern

The awslogs-multiline-pattern option defines a multi-line 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.

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

Note

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

Consider the following log stream, where each log message should start with the pattern INFO:

INFO A message was logged
INFO Another multi-line message was logged
     Some random message
INFO Another message was logged

You can use the regular expression of ^INFO:

$ docker run \
    --log-driver=awslogs \
    --log-opt awslogs-region=us-east-1 \
    --log-opt awslogs-group=myLogGroup \
    --log-opt awslogs-multiline-pattern='^INFO' \
    ...

This parses the logs into the following CloudWatch log events:

# First event
INFO A message was logged

# Second event
INFO Another multi-line message was logged
     Some random message

# Third event
INFO Another message was logged

tag

Specify tag as an alternative to the awslogs-stream option. tag interprets Go template markup, such as {{.ID}}, {{.FullID}} or {{.Name}} docker.{{.ID}}. See the tag option documentation for details on supported template substitutions.

When both awslogs-stream and tag are specified, the value supplied for awslogs-stream overrides the template specified with tag.

If not specified, the container ID is used as the log stream.

Note

The CloudWatch log API doesn't support : in the log name. This can cause some issues when using the {{ .ImageName }} as a tag, since a Docker image has a format of IMAGE:TAG, such as alpine:latest. Template markup can be used to get the proper format. To get the image name and the first 12 characters of the container ID, you can use:
--log-opt tag='{{ with split .ImageName ":" }}{{join . "_"}}{{end}}-{{.ID}}'
the output is something like: alpine_latest-bf0072049c76

awslogs-force-flush-interval-seconds

The awslogs driver periodically flushes logs to CloudWatch.

The awslogs-force-flush-interval-seconds option changes log flush interval seconds.

Default is 5 seconds.

awslogs-max-buffered-events

The awslogs driver buffers logs.

The awslogs-max-buffered-events option changes log buffer size.

Default is 4K.

Credentials

You must provide AWS credentials to the Docker daemon to use the awslogs logging driver. You can provide these credentials with the AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, and AWS_SESSION_TOKEN environment variables, the default AWS shared credentials file (~/.aws/credentials of the root user), or if you are running the Docker daemon on an Amazon EC2 instance, the Amazon EC2 instance profile.

Credentials must have a policy applied that allows the logs:CreateLogStream and logs:PutLogEvents actions, as shown in the following example.

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