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 |
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.
Users can use the --log-opt NAME=VALUE flag to specify additional Fluentd logging driver options.
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
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 nameAt 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.
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.
Write a configuration file (test.conf) to dump input logs:
<source> @type forward </source> <match docker.**> @type stdout </match>
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
Start one or more containers with the fluentd logging driver:
$ docker run --log-driver=fluentd your/application