Tutorial:

1. Create a jenkins user on a Docker node

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sudo useradd -d /var/lib/jenkins jenkins
sudo passwd jenkins
sudo mkdir /var/lib/jenkins/.ssh
sudo touch /var/lib/jenkins/.ssh/authorized_keys
sudo chmod 600 /var/lib/jenkins/.ssh/authorized_keys
sudo chmod 700 /var/lib/jenkins/.ssh
cd /var/lib/
sudo chown -R jenkins:jenkins jenkins
cd jenkins
ls -alh

Change shell to Bash for jenkins user

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sudo vim /etc/passwd

Replace sh to bash for jenkins user. Save and exit

Login as jenkins user.

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sudo su - jenkins

2. Install Java 11 open JDK on a Docker node

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sudo zypper install java-11-openjdk

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sudo apt install openjdk-11-jdk

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sudo dnf install java-11-openjdk

3. Check Java version

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java -version

4. Install Git on a Docker node

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sudo zypper install git

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sudo apt install git

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sudo dnf install git

5. Generate RSA key for Docker node on a Jenkins server

Log to a master Linux server where Jenkins is installed. and switch to a jenkins user.

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sudo su - jenkins

Now you need to generate RSA keys for a Docker node. Do not forget to set a passphrase. You will add it later in Jenkins node management panel.

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ssh-keygen -t rsa -C "The access key for Docker node" -f /var/lib/jenkins/.ssh/id_rsa_docker_node

6. Copy the RSA public key from Jenkins server to Docker node. Use the IP address of the Docker node.

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ssh-copy-id -i id_rsa_docker_node.pub jenkins@10.10.0.121

7. Disable the password login, empty passwords and root login in /etc/ssh/sshd_config on Jenkins server and Docker node.

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# Deny access for root via ssh
sed -i 's/PermitRootLogin yes/PermitRootLogin no/g' /etc/ssh/sshd_config
# Deny password authentication via ssh
sed -i 's/#PasswordAuthentication yes/PasswordAuthentication no/g' /etc/ssh/sshd_config
# Deny using empty passwords
sed -i 's/#PermitEmptyPasswords no/PermitEmptyPasswords no/g' /etc/ssh/sshd_config
# Enable public key authentication
sed -i 's/#PubkeyAuthentication yes/PubkeyAuthentication yes/g' /etc/ssh/sshd_config

Restart ssh daemon

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systemctl restart sshd.service

8. Check can you login using private RSA key after disabling password login.

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ssh -i id_rsa_docker_node jenkins@10.10.0.121

9. Add a Linux node to a master Linux server with Jenkins

• Login to Jenkins web panel: http://10.10.0.113:8080
• Then click Manage Jenkins → Manage nodes and clouds
• Click + New Node on the left side panel.
• Provide a node name
• Select permanent agent
• Set the description the same as node name
• Set number of executors to 1 (it can be increased later)
• Set remote root directory to /var/lib/jenkins
• Set the label docker
• Usage: use this node as much as possible
• Launch method: Launch agents via SSH
• Host: provide the IP address of the Docker node
• Credentials → add → select Jenkins
• Kind - choose from the dropdown list SSH username with private key
• Provide a username: jenkins
• Select enter directly
• Paste the private key copied from the id_rsa_docker_node on a master Linux server with Jenkins (see the part: Generate RSA key for Docker node on a Jenkins server)
• In the Description field provide a friendly name like RSA key for jenkins DOcker node or anything like that that will easily identify the credentials.
• Provide a passphrase to this RSA private key you generated previously on a master Linux server.
• Click add
• Select newly created credentials from a dropdown list
• Host Key Verification Strategy: choose: Known hosts file Verification Strategy
• Availability: Keep this agent online as much as possible
• In node properties select/check Environment variables and Tools Locations
• In Environment variables section add:
• Name: JAVA_HOME
• Value: /usr/bin/java
• In Tools Locations section add:
• Name: Git (default)
• Value: /usr/bin/git
• Click save

10. Set the treshold for free space on a node
11. Extend var logical volume

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sudo lvextend -L +2G /dev/mapper/docker--vg-var
sudo resize2fs /dev/mapper/docker--vg-var
df -kTh /var

12. Cleanup of the /var/tmp directory - explanation with examples

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sudo find /var/tmp -type -f -mtime -1 -exec rm {} \;
sudo find /var/tmp -type -f -mtime -1 -delete
sudo find /var/tmp -type -f -mtime -1 | xargs rm