moby--moby/docs/reference/logging/fluentd.md

Fluentd logging driver

The fluentd logging driver sends container logs to the Fluentd collector as structured log data. Then, users can use any of the various output plugins of Fluentd to write these logs to various destinations.

In addition to the log message itself, the fluentd log driver sends the following metadata in the structured log message:

Field	Description
container_id	The full 64-character container ID.
container_name	The container name at the time it was started. If you use docker rename to rename a container, the new name is not reflected in the journal entries.
source	stdout or stderr

The docker logs command is not available for this logging driver.

Usage

Some options are supported by specifying --log-opt as many times as needed:

• fluentd-address: specify host:port to connect localhost:24224
• fluentd-tag: specify tag for fluentd message, which interpret some markup, ex {{.ID}}, {{.FullID}} or {{.Name}} docker.{{.ID}}

Configure the default logging driver by passing the --log-driver option to the Docker daemon:

docker --log-driver=fluentd

To set the logging driver for a specific container, pass the --log-driver option to docker run:

docker run --log-driver=fluentd ...

Before using this logging driver, launch a Fluentd daemon. The logging driver connects to this daemon through localhost:24224 by default. Use the fluentd-address option to connect to a different address.

docker run --log-driver=fluentd --log-opt fluentd-address=myhost.local:24224

If container cannot connect to the Fluentd daemon, the container stops immediately.

Options

Users can use the --log-opt NAME=VALUE flag to specify additional Fluentd logging driver options.

fluentd-address

By default, the logging driver connects to localhost:24224. Supply the fluentd-address option to connect to a different address.

docker run --log-driver=fluentd --log-opt fluentd-address=myhost.local:24224

fluentd-tag

Every Fluentd's event has a tag that indicates where the log comes from. By default, the driver uses the docker.{{.ID}} tag. Use the fluentd-tag option to change this behavior.

When specifying a fluentd-tag value, you can use the following markup tags:

• {{.ID}}: short container id (12 characters)
• {{.FullID}}: full container id
• {{.Name}}: container name

Note regarding container names

At startup time, the system sets the container_name field and {{.Name}} in the tags to their values at startup. If you use docker rename to rename a container, the new name is not be reflected in fluentd messages. Instead, these messages continue to use the original container name.

Fluentd daemon management with Docker

About Fluentd itself, see the project webpage and its documents.

To use this logging driver, start the fluentd daemon on a host. We recommend that you use the Fluentd docker image. This image is especially useful if you want to aggregate multiple container logs on a each host then, later, transfer the logs to another Fluentd node to create an aggregate store.

Testing container loggers

1. Write a configuration file (test.conf) to dump input logs:

    <source>
      @type forward
    </source>
   
    <match docker.**>
      @type stdout
    </match>
   

2. Launch Fluentd container with this configuration file:

    $ docker run -it -p 24224:24224 -v /path/to/conf/test.conf:/fluentd/etc -e FLUENTD_CONF=test.conf fluent/fluentd:latest
   

3. Start one or more containers with the fluentd logging driver:

    $ docker run --log-driver=fluentd your/application