I was trying to read a file with Java.io.File in a Jenkins Groovy Scripted Pipeline on a non-master node. I kept getting an exception that the file was not found (java.io.FileNotFoundException)

Turns out that Java code written in scripted pipelines (Groovy) runs on the master node: https://issues.jenkins-ci.org/browse/JENKINS-37577. This is as-designed behavior, and accessing files in the workspace on a non-master node should use the readFile function in the Pipeline Basic Steps DSL https://jenkins.io/doc/pipeline/steps/workflow-basic-steps/#pwd-determine-current-directory

I’m thoroughly embarrassed at how many failed Jenkins jobs and alerts I’ve triggered while discovering this.