# Fluentd logging driver The `fluentd` logging driver sends container logs to the [Fluentd](http://www.fluentd.org/) collector as structured log data. Then, users can use any of the [various output plugins of Fluentd](http://www.fluentd.org/plugins) 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](http://www.fluentd.org) and [its documents](http://docs.fluentd.org/). To use this logging driver, start the `fluentd` daemon on a host. We recommend that you use [the Fluentd docker image](https://registry.hub.docker.com/u/fluent/fluentd/). 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: @type forward @type stdout 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