<!-- vim: set syn=markdown : -->
<!--
    Licensed to the Apache Software Foundation (ASF) under one or more
    contributor license agreements.  See the NOTICE file distributed with
    this work for additional information regarding copyright ownership.
    The ASF licenses this file to You under the Apache License, Version 2.0
    (the "License"); you may not use this file except in compliance with
    the License.  You may obtain a copy of the License at

         http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
-->
#set($dollar = '$')
#set($h1='#')
#set($h2='##')

$h1 Log4j Docker Support

Log4j supports Docker by providing a Lookup to retrieve container information.

$h2 Accessing Docker

The Log4j Docker support requires access to the Docker REST interface. In practical terms this means the
application either needs access to unix:///var/run/docker.sock through a volume mount (not recommended),
bind Docker to another host/port or unix socket. or use a proxy application to provide access. The
[Log4j Spring Cloud sample application](https://github.com/apache/logging-log4j2/tree/master/log4j-spring-cloud-config/log4j-spring-cloud-config-samples/log4j-spring-cloud-config-sample-application)
uses a socat proxy to access Docker.

$h2 Lookup Attributes

Log4j Docker provides access to the following container attributes:

* containerId - The full id assigned to the container.
* containerName - The name assigned to the container.
* imageId - The id assigned to the image.
* imageName - The name assigned to the image.
* shortContainerId - The first 12 characters of the container id.
* shortImageId - The first 12 characters of the image id.

#set( $D = '${' )
#set( $container = 'docker:containerId}')
Attributes may be accessed by adding
```
$D$container
```
to the configuration. Note that docker variables are only resolved once during logging initializaton so they
shouldn't be referenced with more than one '$' character.

$h2 Requirements
Log4j Docker requires Log4j Core, Log4j API and a minimum of Java 8.
For more information, see [Runtime Dependencies](../runtime-dependencies.html).