Demo Log Recorder

In this guide, we’ll show you how to create and manage loggers in Jenkins for effective troubleshooting and debugging. Jenkins offers multiple methods to adjust logging levels—ideal for diagnosing issues in plugins, pipelines, and integrations.

Logging Configuration Options

You can configure custom logging in Jenkins using one of these five approaches:

1. Add a Logger via the Jenkins UI (recommended)
2. Initialize via a Groovy Script
3. Use a Java Util Logging Properties File
4. File System Custom Log Recorder
5. XML Configuration via the UI (non-persistent)

1. Add a Logger via the Jenkins UI

For dynamic control over logging, the Jenkins UI is the easiest option. For example, to troubleshoot the Kubernetes cloud plugin:

1. Go to Manage Jenkins → System Log.
2. Click Add new log recorder, provide a name, then add the package or logger and select the desired level.

2. Initialize via a Groovy Script

Place a Groovy file under JENKINS_HOME/init.groovy.d/ to set log levels at startup:

import java.util.logging.Level
import java.util.logging.Logger

Logger.getLogger("hudson.plugins.git.GitStatus").setLevel(Level.SEVERE)
Logger.getLogger("hudson.security.csrf.CrumbFilter").setLevel(Level.SEVERE)

3. Java Util Logging Properties File

Drop a logging.properties file into $JENKINS_HOME:

.level = INFO
handlers = java.util.logging.ConsoleHandler

java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter

4. File System Custom Log Recorder

Create XML definitions under the Jenkins home directory:

$JENKINS_HOME/
  log/
    kb-article.xml   # Custom log recorder definition
  logs/
    custom/
      kb-article.log # Recorder output file

5. XML Configuration via the UI (Non-Persistent)

You can also paste default logger settings directly in the UI (resets on restart):

<?xml version="1.1" encoding="UTF-8"?>
<log>
  <name>kb-article</name>
  <targets>
    <target>
      <name>org.jenkinsci.plugins.saml</name>
      <level>300</level>
    </target>
    <target>
      <name>org.pac4j</name>
    </target>
  </targets>
</log>

Example: Debugging Kubernetes Cloud Connection

When testing your Kubernetes cloud in Jenkins, you might see a generic error:

Error testing connection https://7b730b7f-4e4e-471d-929a-23267474384a.k8s.onddi...
io.fabric8.kubernetes.client.KubernetesClientException: Failure executing: GET at: https://7b7.../pods. 
Message: pods is forbidden: User "system:serviceaccount:jenkins:jenkins-service-account" 
cannot list resource "pods" ... Received status: Status(apiVersion=v1, code=403...))

To capture HTTP-level details:

1. Go to Manage Jenkins → System Log.
2. Click Add new log recorder, name it (e.g., k8s-logs), and set level to All.
3. Search for Kubernetes and select io.fabric8.kubernetes.client or the specific subpackage.

After saving, retry the connection and then refresh the log recorder view to see detailed HTTP exchanges:

Nov 10, 2024 5:34:35 PM FINE io.fabric8.kubernetes.client.utils.HttpClientUtils getHttpClientFactory
Using httpclient io.fabric8.kubernetes.client.okhttp.OkHttpClientFactory factory
Nov 10, 2024 5:34:35 PM FINEST io.fabric8.kubernetes.client.HttpLoggingInterceptor$HttpLogger logStart
-HTTP START-
Nov 10, 2024 5:34:35 PM FINEST io.fabric8.kubernetes.client.HttpLoggingInterceptor$HttpLogger logRequest
> GET https://7b7b35ef-.../namespaces/jenkins-123/pods
> Authorization: Bearer eyJh...
> User-Agent: fabric8-kubernetes-client/6.1.0
< 403 Forbidden
Nov 10, 2024 5:34:35 PM FINEST io.fabric8.kubernetes.client.HttpLoggingInterceptor$HttpLogger logResponse
< content-type: application/json
...
Nov 10, 2024 5:34:35 PM FINE io.fabric8.kubernetes.client.impl.BaseClient close
The client and associated httpclient ... have been closed...

These entries reveal the full request headers, status codes, and JSON payload.

Example: Successful Connection

With correct RBAC and service account settings, the UI will show a one-line success. Jenkins will still record the detailed HTTP lifecycle if debug logging is enabled:

-HTTP START-
> GET https://bhb3f7f-4e4d-99a2-237c7438a.k8s.digitalocean.com/api/v1/namespaces/jenkins/pods
... (headers)
-HTTP END-
Nov 10, 2024 5:34:35 PM FINE io.fabric8.kubernetes.client.impl.BaseClient close

You can also log the Kubernetes version:

{
  "major": "1",
  "minor": "29",
  "gitVersion": "v1.29.9",
  "gitCommit": "114a1f58037bd7f90d9e630e591c5e52dd9b298",
  "gitTreeState": "clean",
  "buildDate": "2020-09-11T20:19:54Z",
  "goVersion": "go1.22.6",
  "compiler": "gc",
  "platform": "linux/amd64"
}

Cleanup

After you've resolved the issue, delete any custom log recorders or reset log levels to restore Jenkins’s default performance.

Links and References

• Jenkins System Log
• Kubernetes RBAC Documentation
• Fabric8 Kubernetes Client