When defining environment variables both in a declarative pipeline running a docker agent, and in the jenkins master process environment itself, then the environment variable is missing in the docker agent.

Scenario:

Jenkins setup:

Using jenkins:lts docker image, with docker socket forwarded in the jenkins docker container for it to use docker agents; with extra environment variables:

$ docker run -e FOO=bar -e FOO2=bar -e FOO3=bar -v /var/run/docker.sock:/var/run/docker.sock -v $(which docker):/usr/bin/docker --init -v jenkins_home:/var/jenkins_home -p 8080:8080 -p 50000:50000 --name jenkins jenkins/jenkins:lts
# hack to add missing depencies on the docker cli, and fix permissions issues
$ docker exec -u 0 jenkins bash -c "apt-get update && apt-get install libltdl7 && chown -R jenkins:jenkins /var/run/docker.sock"

Setup jenkins with usual plugins (no manual selection).

Pipeline job:

Create a pipeline with the following declarative pipeline:

pipeline {
    agent { docker 'ubuntu:16.04' }

    environment {
        FOO = 'bar'
        FOO2 = 'different'
    }
    stages {
        stage('Test') {
            steps {
                sh 'echo FOO: ${FOO:-error}'
                sh 'echo FOO2: ${FOO2:-error}'
                sh 'echo FOO3: ${FOO3:-error}'
            }
        }
    }
}

Run the job

[env-bug] Running shell script
+ echo FOO: error
FOO: error
[Pipeline] sh
[env-bug] Running shell script
+ echo FOO2: different
FOO2: different
[Pipeline] sh
[env-bug] Running shell script
+ echo FOO3: error
FOO3: error

Analysis

Scenario explanation:

• start jenkins with env vars FOO=bar and FOO2=bar and FOO3=bar
• pipeline redeclares FOO=bar (same value) and FOO3=different (different value)
• result: FOO disappears in the shell environment in docker agent, FOO2 is OK, FOO3 is not there (not forwarded from jenkins environment, it's an extra test).