Creating an RSA Key for Jenkins and GitLab

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Tiempo de lectura: 2 minutos

You explain how to add an RSA key in Jenkins to authenticate with GitLab:

In the Jenkins server (or your local machine), execute:

bash

ssh-keygen -t rsa -b 4096 -C "[email protected]"

Save the keys, for example in ~/.ssh/id_rsa_jenkins.

In a Pipeline (Jenkinsfile):

groovy

pipeline { agent any stages { stage('Checkout') { steps { git credentialsId: 'gitlab-ssh-key', url: '[email protected]:usuario/repositorio.git' } } }

A Groovy Pipeline

You can manually test the connection on your Jenkins server:

bash

ssh -i ~/.ssh/id_rsa_jenkins -T [email protected]

You should see a welcome message from GitLab if everything is correct.

If an error appears:

 returned status code 128: stdout: stderr: No ED25519 host key is known for gitlab.com and you have requested strict checking. Host key verification failed. fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.

Option 1: From Jenkins Server (Recommended)

Connect to Jenkins server/container and run as jenkins:

bash

# Change to jenkins user sudo su -s /bin/bash jenkins # Add gitlab.com to known_hosts ssh-keyscan -t rsa,ecdsa,ed25519 gitlab.com >> ~/.ssh/known_hosts # Verify that it was added cat ~/.ssh/known_hosts | grep gitlab.com

Option 2: From Jenkins Configuration (No Server Access)

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  • Go to Manage Jenkins → Security → Git Host Key Verification Configuration
  • In Host Key Verification Strategy, select:
    • Manually provided keys → paste the output of:
    1. O (less secure) No verification → only for testing

    Option 3: If you use Jenkins in Docker

    bash

    docker exec -u jenkins <container_id> ssh-keyscan -t rsa,ecdsa,ed25519 gitlab.com >> /var/jenkins_home/.ssh/known_hosts

    Check the functionality

    Test the connection from the Jenkins user:

    bash

    sudo su -s /bin/bash jenkins ssh -T [email protected]

    You should see:

    Welcome to GitLab, @your_user!

    Why is this happening? SSH has strict host verification by default. If gitlab.com is not in known_hosts, it rejects the connection even with a correct RSA key. The ssh-keyscan simply pre-aproves the fingerprint of GitLab.

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