Configure logging programmatically in Scala/Play - scala

Question

The Play framework requires (by default) that you configure logging through a logback.xml file. I'd like to build my log appenders through code so I can fetch parameters at runtime (e.g. the graylog destination for the logs is fetched from the deployment environment, rather than baking it in statically through an XML file).
This sort of thing is fairly easy to achieve in Java (by overriding logging factories and the like), I wondered if the same were possible in Play.

Answer 1

Yes, you can configure logback programmatically, see: https://akhikhl.wordpress.com/2013/07/11/programmatic-configuration-of-slf4jlogback/
But I wouldn't recommend it. For starters it's a verbose API that isn't pleasant to work with. Beyond that, it generally nice for configuration to be declarative (even if it is in XML in this case).
For your usecase, Logback's XML does support variables which can come from System properties or Environment variables: https://logback.qos.ch/manual/configuration.html#definingProps
However, you probably want a different config across environments (no greylog locally). I think many projects do that by specifying the logback XML location as a system property at startup: https://logback.qos.ch/manual/configuration.html#configFileProperty
Alternatively, I suspect greylog has some method of watching a file to pickup your logging. That's what we do for picking up logs in Splunk in my team. We don't want to make a change to our code when someone reconfigures Splunk/Greylog.

Answer 2

The solution I used in the end was to use a logback contextlistener to populate the context with the parameters pulled from the environment. The listener can be added as follows to the logback.xml:
<contextListener class="LoggerStartup"/>
The LoggerStartup can then populate the context, which I achieved through AWS SSM (see the simplified code below).
class LoggerStartup extends ContextAwareBase with LoggerContextListener with LifeCycle {
override def start() = {
val context = getContext()
val graylogUrl = ... // Go get value from remote store
context.putProperty("GRAYLOG_URL", graylogUrl)
}
}
And then referenced this context variable in the logback file:
<appender name="GELF UDP APPENDER" class="me.moocar.logbackgelf.GelfUDPAppender">
<remoteHost>${GRAYLOG_URL}</remoteHost>
...
</appender>