Jenkins ssh remote host connection fails

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06-10-2024

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Jenkins SSH Remote Host Connection Fails: Troubleshooting Guide

Connecting to a remote host via SSH is a fundamental part of many Jenkins pipelines. This allows for tasks like running scripts, deploying applications, or interacting with other systems. However, encountering connection failures can bring your workflow to a halt. This article will guide you through troubleshooting common causes of Jenkins SSH connection errors and provide solutions to get your pipeline running smoothly.

The Problem:

Jenkins attempts to connect to a remote host via SSH but fails. This could manifest as a build error, a timeout, or an inability to execute remote commands.

Scenario & Code Example:

Let's assume your Jenkins pipeline attempts to connect to a remote server named "remote_server" with the following snippet:

stage('Deploy to remote server') {
    steps {
        sshServer remote: 'remote_server',
               credentialsId: 'ssh_credentials',
               command: 'sudo systemctl restart my_app'
    }
}

This pipeline utilizes the "ssh" plugin and attempts to execute a command on the remote server. If the connection fails, you might see errors like:

• "SSH: Connection timed out"
• "SSH: Connect failed: host unreachable"
• "SSH: Could not connect to server"

Troubleshooting & Solutions:

1. Connectivity:

   • Network Connectivity: Ensure that your Jenkins server can reach the remote server over the network. Check for firewall rules, network configurations, and connectivity issues.
   • SSH Port: Verify that the SSH port (typically 22) is open on the remote server and accessible from the Jenkins server.
   • DNS Resolution: Confirm that the hostname used in the Jenkins pipeline resolves to the correct IP address on the remote server.

2. SSH Credentials:

   • Credentials Validity: Double-check that the SSH credentials used in your Jenkins pipeline are correct and have the necessary permissions to access the remote server.
   • Key Permissions: If you are using SSH keys, ensure the private key file has the correct permissions (usually 600) and is accessible by the Jenkins user.
   • Passwordless Login: If possible, configure passwordless SSH login for the Jenkins user on the remote server to prevent interactive password prompts.

3. Jenkins Plugins and Configurations:

   • SSH Plugin Version: Ensure that the "SSH" plugin installed in your Jenkins instance is up-to-date. Older versions might have compatibility issues.
   • SSH Plugin Configuration: Review the SSH plugin configuration in your Jenkins instance. Check if the "Remote Server" settings match your remote host and if the "Credentials" are correctly configured.

4. Remote Server Configuration:

   • SSH Daemon: Verify that the SSH daemon is running on the remote server. You can check this using the command ps aux | grep sshd.
   • SSH Settings: Review the SSH server configuration file (/etc/ssh/sshd_config) on the remote server. Ensure that:
     • Port: The SSH port is set to 22 or the desired value.
     • AllowUsers: The Jenkins user is allowed to connect via SSH.
     • PasswordAuthentication: If you are using key-based authentication, ensure that PasswordAuthentication is set to "no".
   • Firewall: Ensure that the SSH port is not being blocked by the remote server's firewall.

5. Troubleshooting Tools:

   • SSH Debugging: Use the ssh -vvv command to enable verbose SSH debugging and identify issues with the connection attempt.
   • Network Monitoring: Utilize tools like ping or traceroute to test network connectivity between the Jenkins server and the remote server.

Additional Tips:

• Jenkins logs: Check the Jenkins logs for detailed information on the SSH connection failures.
• Testing outside Jenkins: Manually test the SSH connection from the Jenkins server to the remote server using an SSH client to confirm connectivity and configurations.
• Remote host access: If possible, log into the remote server and check for any relevant error messages or logs related to SSH.

Conclusion:

By systematically analyzing and addressing these common causes of Jenkins SSH connection failures, you can diagnose and resolve the issue. Remember to check each component of the connection, from network connectivity to plugin settings and remote server configurations. Following these troubleshooting steps will help you restore your Jenkins pipeline's SSH functionality and ensure smooth remote execution.