Dynamic log level changes with Logback in a docker app

Question

Logback has a feature to scan changes in logback.xml (per this) - this is a great feature which allows long running applications to be shipped with INFO as default level to be changed to DEBUG when something has to be briefly investigated.

But in my recent app (hosted on my company's K8s cluster as a Docker container), am unable to use the above feature because:

dont yet have the provision to host external volumes wherein I can put my logback.xml (to be changed by developers during debugging)
dont yet have the provision to change environment variables in a running container without a restart
dont have a JNDI server to map log variables

Given this, is there a way I can build a provision for developers to change the logging level of my application at runtime without an app/container restart?

score 2 · Answer 1 · answered May 22 '20 at 21:05

I'm not sure if you're also forbidden to mount configmap into a container, as you haven't mentioned it.
But on the off chance that you're not, you can create a configmap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: logback-conf
data:
  logback.xml: |
    <configuration>
      <root level="debug">
        <appender-ref ref="STDOUT" />
      </root>
    </configuration>

And add it to the container, as follows:

  containers:
    - name: app
      volumeMounts:
      - name: config
        # The conf will be mounted at /app/logback.xml
        mountPath: /app
...
  volumes:
    - name: config
      configMap:
        name: logback-conf

If you aren't allowed to even inject a configmap (which to my knowledge doesn't cause downtime), there's really not much you can do

score 2 · Accepted Answer · answered May 24 '20 at 09:10

I have a similar problem: I need to change the application log level at runtime without restart the spring boot application. In my situation, I'm not working in a docker context, but I think the solution to our problem is the same.

After research I found 3 possible solutions:

change log file at runtime
enable JMX and work with JConsole to change log levels
use Spring Boot Admin.

The 3 solution is the best, if your app is a Spring Boot app. You can read the following tutorial Changing the logging level at runtime.

You can found an example how to enable the Admin interface on Github.

Dynamic log level changes with Logback in a docker app

2 Answers2