skywalking-java/docs/en/setup/backend/dynamical-logging.md

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# Dynamical Logging
The OAP server leverages `log4j2` to manage the logging system. `log4j2` supports changing the configuration
at runtime, but you have to update the XML configuration file manually, which could be time-consuming and prone to manmade mistakes.
Dynamical logging, which depends on dynamic configuration, provides us with an agile way to update all OAP `log4j`
configurations through a single operation.
The key of the configuration item is `core.default.log4j-xml`, and you can select any of the configuration implements
to store the content of `log4j.xml`. In the booting phase, once the core module gets started, `core.default.log4j-xml`
would come into the OAP log4j context.
If the configuration is changed after the OAP has started, you have to wait for a while for the changes to be applied.
The default value is `60` seconds, which you could change through `configuration.<configuration implement>.peroid` in `application.yaml`.
If you remove `core.default.log4j-xml` from the configuration center or disable the configuration module, `log4j.xml` in the `config` directory would be affected.
> Caveat: The OAP only supports the XML configuration format.
This is an example on how to config dynamical logging through a ConfigMap in a Kubernetes cluster. You may set up other configuration
clusters following the same procedures.
```yaml
apiVersion: v1
data:
core.default.log4j-xml: |-
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout charset="UTF-8" pattern="%d - %c - %L [%t] %-5p %x - %m%n"/>
</Console>
</Appenders>
<Loggers>
<logger name="io.grpc.netty" level="INFO"/>
<logger name="org.apache.skywalking.oap.server.configuration.api" level="TRACE"/>
<logger name="org.apache.skywalking.oap.server.configuration.configmap" level="DEBUG"/>
<Root level="WARN">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>
kind: ConfigMap
metadata:
labels:
app: collector
release: skywalking
name: skywalking-oap
namespace: default
```