Fix Jenkins Plugin Deprecation Warnings After Upgrades (2026)

The Jenkins controller’s core component is failing to send metrics to the Prometheus exporter due to a mismatch in the expected metric format, caused by an outdated Prometheus plugin.

Common Causes and Fixes

Outdated Prometheus Plugin:
- Diagnosis: Check the Jenkins plugin manager for the version of the "Prometheus metrics" plugin. If it’s older than 3.1.0, it’s likely the culprit. You might also see errors in the Jenkins system log like java.lang.NoSuchMethodError: io.prometheus.client.CollectorRegistry.metricFamilySamples()Ljava/util/Collection;.
- Fix: Navigate to "Manage Jenkins" -> "Plugins" -> "Available plugins". Search for "Prometheus metrics". If an update is available, select it and click "Install without restart" or "Download now and install after restart".
- Why it works: Newer versions of the Prometheus plugin use updated Prometheus client libraries that are compatible with the metrics format expected by the Prometheus exporter. The NoSuchMethodError indicates that a method expected by the exporter (likely metricFamilySamples) no longer exists or has changed signature in the version of the client library bundled with the older plugin.
Incorrect Prometheus Exporter Configuration (Scrape Interval Too Fast):
- Diagnosis: Examine your Prometheus configuration file (prometheus.yml). Look for the scrape_interval setting for the Jenkins target. If it’s set to a very low value (e.g., 5s or 10s) and you’re seeing intermittent 500 Internal Server Error responses from Jenkins when Prometheus scrapes it, this could be an issue.
- Fix: Increase the scrape_interval in prometheus.yml to at least 30s or 60s. For example:
```
scrape_configs:
  - job_name: 'jenkins'
    static_configs:
      - targets: ['your-jenkins-host:9108'] # Assuming default metrics port
    scrape_interval: 30s
```
- Why it works: The Jenkins Prometheus plugin needs a small amount of time to gather and format its metrics. Scraping too frequently can overwhelm the plugin or the Jenkins controller, leading to errors. Increasing the interval gives Jenkins more breathing room.
Jenkins Controller Resource Constraints:
- Diagnosis: Monitor the CPU and memory usage of your Jenkins controller JVM. If you see sustained high CPU utilization (>80%) or frequent OutOfMemory errors in the Jenkins logs, the controller might be struggling to generate metrics.
- Fix: Increase the JVM heap size for your Jenkins controller. For example, if you’re using jenkins.sh or jenkins.war, you might modify the JENKINS_OPTS environment variable:
```
export JENKINS_OPTS="-Xmx4096m -Xms1024m"
```
  Then restart Jenkins.
- Why it works: Generating metrics, especially for large Jenkins instances with many jobs and builds, can be memory and CPU intensive. Providing more heap space allows the JVM to manage its memory more effectively and reduces the likelihood of garbage collection pauses that could interfere with metric generation.
Network Connectivity Issues Between Prometheus and Jenkins:
- Diagnosis: Use curl from the Prometheus server to attempt to scrape the Jenkins metrics endpoint. For example: curl http://your-jenkins-host:9108/metrics. If this command fails with connection refused, timeout, or other network errors, there’s a connectivity problem.
- Fix:
  - Firewall Rules: Ensure that firewalls on both the Jenkins host and any intermediate network devices allow traffic on the Jenkins metrics port (default 9108) from the Prometheus server’s IP address.
  - DNS Resolution: Verify that the Prometheus server can resolve the hostname of your Jenkins controller.
  - Jenkins Configuration: Double-check the jenkins.metrics.PrometheusEndpoint configuration in Jenkins (Manage Jenkins -> Configure System -> Prometheus metrics) to ensure the port and binding address are correct.
- Why it works: Prometheus needs to be able to reach the /metrics endpoint exposed by the Jenkins Prometheus plugin. Network misconfigurations are a fundamental barrier to this communication.
Jenkins Metrics Plugin Not Enabled or Configured:
- Diagnosis: Go to "Manage Jenkins" -> "Configure System". Scroll down to the "Prometheus metrics" section. Check if the "Enable Prometheus endpoint" checkbox is ticked and if the port (default 9108) is correctly specified and not in use by another service.
- Fix: Ensure the "Enable Prometheus endpoint" checkbox is checked. If the port is already in use, change it to an available port (e.g., 9109). Save the configuration and restart Jenkins if prompted.
- Why it works: The Prometheus plugin needs to be explicitly enabled and configured with a listening port for Prometheus to scrape metrics from. If it’s disabled or configured on a port that’s already occupied, Prometheus won’t be able to connect.
Java Version Incompatibility with Prometheus Plugin:
- Diagnosis: Check the Java version your Jenkins controller is running on (java -version in your Jenkins installation directory). Some older versions of the Prometheus plugin might have dependencies or require a minimum Java version that is not met by your current setup. Conversely, very new Java versions might also introduce subtle incompatibilities.
- Fix: Ensure your Jenkins controller is running on a Java version supported by both Jenkins and the installed Prometheus plugin. For recent Jenkins versions and Prometheus plugins, Java 11 or 17 are common recommendations. Update your JAVA_HOME environment variable or the JVM used by Jenkins accordingly.
- Why it works: The Prometheus client libraries used by the plugin are compiled against specific Java versions. Mismatches can lead to class loading errors or unexpected runtime behavior, preventing metrics from being generated or exposed correctly.

After resolving these issues, the next error you might encounter is related to the jenkins_build_duration_seconds metric showing up as NaN or missing entirely if the Jenkins pipeline metrics gathering is not properly configured or if specific plugins (like Pipeline Metrics) are also outdated or misconfigured.