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Usually, Jenkins master and Jenkins agent are located in the same network, therefore it is quite easy to adopt Jenkins agents using SSH. This time we will talk about the situation when Jenkins master and bunch of other DevOps tools are running in "network A" and Jenkins agents are running in "network B". Quite often connections from A to B are rejected, however, connections from B to A are accepted. There might be various reasons, in general, network B has elevated security expectations. A typical setup is Jenkins master located in public cloud and Jenkins agent(s) located in a private customer network. Private customer network might be needed in such because some sort of higher data privacy requirements must be matched or some specialised hardware is present in customer premises and it cannot be accessible directly from the public internet.

Solution

Recommended The recommended solution is master/agent setup, when the master runs in a public environment and agent is running on a server located in a private network. Agent The agent is also called "on-premise executor" (OPE). Jobs are then performing jobs/tasks on such agent in internal/private networks. Jenkins Agent has an active connection from the internal network to internet accessible Jenkins Master via recommended JNLP port tcp/9000 and keeps listening to builds/jobs. Port can be changed, but we will keep talking about 9000. NO direct or NAT network connection is required from the internet to internal network. It is a secure and simple solution.

Gliffy Diagram
namejenkins-agent-master
pagePin1

Requirements:

  • Network
    • firewall opening for port tcp/9000 from relevant source agent(s) IP(s) in internal network towards internet in general (destination 0.0.0.0)
      • network layer (using TDS portal network functionality)
      • operating system layer (firewalld if needed)
  • Jenkins master
    • running in public
    • listening on JNLP port tcp/9000
    • node added according to the following steps
      • Go to https://jenkins.xxx.tds.customerx.com/computer/new (remember to use correct URL of your Jenkins master)
      • Set "Node name" to relevant name useful for you
      • Choose "Permanent"
      • Set "Remote root directory" to "/home/jenkinsope"
      • Set "Launch method" to "Launch agent by connecting it to the master" previously called "Launch agent via Java Web Start"
    • copy secret/token for connecting agent
      • Go to https://jenkins.xxx.tds.customerx.com/computer/XXX (remember to use correct URL of your Jenkins master and replace XXX with the name of your node)
      • You will see something like:

        Code Block
        Run from agent command line:
        
        java -jar agent.jar -jnlpUrl https://jenkins.xxx.tds.customerx.com/computer/test/slave-agent.jnlp -secret 8b2911d98400bad5d45635b812b5f2e8e7c1d216bbbae9422a3ba57c691bf762 -workDir "/home/jenkinsope"
        Run from agent command line, with the secret stored in a file:
        
        echo 8b2911d98400bad5d45635b812b5f2e8e7c1d216bbbae9422a3ba57c691bf762 > secret-file
        java -jar agent.jar -jnlpUrl https://jenkins.xxx.tds.customerx.com/computer/test/slave-agent.jnlp -secret @secret-file -workDir "/home/jenkinsope"

        Please copy only the secret, which is for example in this case "8b2911d98400bad5d45635b812b5f2e8e7c1d216bbbae9422a3ba57c691bf762"

  • Jenkins agent node (slave) - or so-called "on-premise executor"
    • running on a server in internal network(s)
    • agent service(s) with service auto-start to assure automatic re-connect to Jenkins master at any time even after server reboot
      • Install dependencies
        • CentOS

          Code Block
          yum install java-1.8.0-openjdk-devel git -y
          # you can install also other dependencies that will be required for your jobs


        • Ubuntu

          Code Block
          apt-get update; apt-get install openjdk-8-jdk git -y
          # you can install also other dependencies that will be required for your jobs


      • Installing agent
        • Prepare a folder for config

          Code Block
          mkdir -p /data/configs


        • Create service file /tmp/jenkinsope.service

          Code Block
          titlejenkinsope.service
          [Unit]
          Description=Jenkins Slave On Premise Executor
          Wants=network.target
          After=network.target
          
          [Service]
          # EnvironmentFile cannnot be used on Debian/Ubuntu anymore - Reference: https://github.com/varnishcache/pkg-varnish-cache/issues/24
          # So we are using drop-in config /etc/systemd/system/jenkinsope.service.d/local.conf
          ExecStart=/usr/bin/java -Xms${JAVA_MEMORY} -Xmx${JAVA_MEMORY} -jar /usr/bin/agent.jar -jnlpUrl ${MASTER_URL}/computer/${SLAVE_NAME}/slave-agent.jnlp -secret ${SECRET} -workDir "${WORK_DIR}"
          User=jenkinsope
          Restart=always
          RestartSec=10
          StartLimitInterval=0
          
          [Install]
          WantedBy=multi-user.target


        • Create config file /data/configs/jenkinsope.conf

          Code Block
          JAVA_MEMORY=512m
          MASTER_URL=https://jenkins.xxx.tds.customerx.com
          SLAVE_NAME=XXX
          SECRET=8b2911d98400bad5d45635b812b5f2e8e7c1d216bbbae9422a3ba57c691bf762
          WORK_DIR=/home/jenkinsope


        • Create script /tmp/jenkinsope-install.sh

          Code Block
          useradd -m -s /bin/bash jenkinsope
          mkdir -p /home/jenkinsope/.ssh
          chmod 700 /home/jenkinsope/.ssh
          touch /home/jenkinsope/.ssh/config
          chmod 600 /home/jenkinsope/.ssh/*
          chown jenkinsope:jenkinsope -R /home/jenkinsope/.ssh
          source /data/configs/jenkinsope.conf
          wget ${MASTER_URL}/jnlpJars/agent.jar -O /usr/bin/agent.jar
          chmod 644 /usr/bin/agent.jar
          install -D -m 644 /tmp/jenkinsope.service /usr/lib/systemd/system/jenkinsope.service
          mkdir -p /etc/systemd/system/jenkinsope.service.d
          echo "[Service]" > /etc/systemd/system/jenkinsope.service.d/local.conf
          sed 's#^#Environment=#g' /data/configs/jenkinsope.conf >> /etc/systemd/system/jenkinsope.service.d/local.conf
          systemctl daemon-reload
          systemctl restart jenkinsope
          systemctl enable jenkinsope
          systemctl status jenkinsope


        • Run install script

          Code Block
          chmod +x /tmp/jenkinsope-install.sh
          /tmp/jenkinsope-install.sh


      • Uninstalling agent (for cleanup purposes or if you messed up something)
        • Create script /tmp/jenkinsope-uninstall.sh

          Code Block
          systemctl disable jenkinsope
          systemctl stop jenkinsope
          rm -f /usr/lib/systemd/system/jenkinsope.service
          rm -rf /etc/systemd/system/jenkinsope.service.d
          systemctl daemon-reload
          userdel -r jenkinsope
          rm -rf /home/jenkinsope


        • Run install script

          Code Block
          chmod +x /tmp/jenkinsope-uninstall.sh
          /tmp/jenkinsope-uninstall.sh


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