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

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aliases = ["/engine/reference/logging/fluentd/"]
title = "Fluentd logging driver"
description = "Describes how to use the fluentd logging driver."
keywords = ["Fluentd, docker, logging, driver"]
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parent = "smn_logging"
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# 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`
 - `tag`: specify tag for fluentd message, which interpret some markup, ex `{{.ID}}`, `{{.FullID}}` or `{{.Name}}` `docker.{{.ID}}`
 - `fail-on-startup-error`: true/false; Should the logging driver fail container startup in case of connect error during startup. Default: true (backwards compatible)
 - `buffer-limit`: Size limit (bytes) for the buffer which is used to buffer messages in case of connection outages. Default: 1M

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

    docker daemon --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

### tag

By default, Docker uses the first 12 characters of the container ID to tag log messages.
Refer to the [log tag option documentation](log_tags.md) for customizing
the log tag format.


### labels and env

The `labels` and `env` options each take a comma-separated list of keys. If there is collision between `label` and `env` keys, the value of the `env` takes precedence. Both options add additional fields to the extra attributes of a logging message.

### fail-on-startup-error

By default, if the logging driver cannot connect to the backend it will fail the entire startup of the container. If you wish to ignore potential connect error during container startup supply the `fail-on-startup-error` flag.

    docker run --log-driver=fluentd --log-opt fail-on-startup-error=false


### buffer-limit

When fluent driver loses connection, or cannot connect at container startup, it will buffer the log events locally for re-transmission. Buffer limit option controls how much data will be buffered locally, **per container**. Specified in bytes.

    docker run --log-driver=fluentd --log-opt buffer-limit=5242880

The above would result to use 5M buffer locally. Keep in mind that during possible connection errors all your containers will start buffering locally and thus might result in considerable memory usage.

## 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://hub.docker.com/r/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:

        <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