Issue

• Best Practice For Using Jenkins REST API

Environment

• CloudBees Jenkins Enterprise - Managed Master (CJEMM)
• CloudBees Jenkins Enterprise - Operations Center (CJEOC)
• CloudBees Jenkins Team (CJT)
• CloudBees Jenkins Platform - Client Master (CJPCM)
• CloudBees Jenkins Platform - Operations Center (CJPOC)
• Jenkins LTS

Resolution

The Jenkins REST API should never be used without the tree parameter. Using the Jenkins REST API without the tree parameter, making a call to /api/json for example will run. However, making a call to /api/json will cause Jenkins by default to respond with some rather arbitrary collection of data,
some of which might not be used and which may be work to compute. The practice of making /api/json calls can cause poor performance issues and high CPU issues.

More information about the tree parameter can be found here $JENKINS_URL/api.

You can check the Jenkins access logs for requests URLs matching the regular expression .*\/api\/(python|json|xml) to see the origins of of unrestricted requests. If necessary, you can block all API calls.

Taming Jenkins JSON API Blog Post