how to setup ssh keys for jenkins to publish via ssh - jenkins

Question

Jenkins requires a certificate to use the ssh publication and ssh commands. It can be configured under "manage jenkins" -> "Configure System"-> "publish over ssh".
The question is: How does one create the certificates?
I have two ubuntu servers, one running Jenkins, and one for running the app.
Do I set up a Jenkins cert and put part of it on the deployment box, or set up a cert on the deployment box, and put part of it on Jenkins? Does the cert need to be in the name of a user called Jenkins, or can it be for any user? We don't have a Jenkins user on the development box.
I know there are a number of incompatible ssh types, which does Jenkins require?
Has anyone found a guide on how to set this all up (how to generate keys, where to put them etc.)?

Answer 1

You will need to create a public/private key as the Jenkins user on your Jenkins server, then copy the public key to the user you want to do the deployment with on your target server.
Step 1, generate public and private key on build server as user jenkins
build1:~ jenkins$ whoami
jenkins
build1:~ jenkins$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/var/lib/jenkins/.ssh/id_rsa):
Created directory '/var/lib/jenkins/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /var/lib/jenkins/.ssh/id_rsa.
Your public key has been saved in /var/lib/jenkins/.ssh/id_rsa.pub.
The key fingerprint is:
[...]
The key's randomart image is:
[...]
build1:~ jenkins$ ls -l .ssh
total 2
-rw------- 1 jenkins jenkins 1679 Feb 28 11:55 id_rsa
-rw-r--r-- 1 jenkins jenkins 411 Feb 28 11:55 id_rsa.pub
build1:~ jenkins$ cat .ssh/id_rsa.pub
ssh-rsa AAAlskdjfalskdfjaslkdjf... jenkins#myserver.com
Step 2, paste the pub file contents onto the target server.
target:~ bob$ cd .ssh
target:~ bob$ vi authorized_keys (paste in the stuff which was output above.)
Make sure your .ssh dir has permissoins 700 and your authorized_keys file has permissions 644
Step 3, configure Jenkins
In the jenkins web control panel, nagivate to "Manage Jenkins" -> "Configure System" -> "Publish over SSH"
Either enter the path of the file e.g. "var/lib/jenkins/.ssh/id_rsa", or paste in the same content as on the target server.
Enter your passphrase, server and user details, and you are good to go!

Answer 2

You don't need to create the SSH keys on the Jenkins server, nor do you need to store the SSH keys on the Jenkins server's filesystem. This bit of information is crucial in environments where Jenkins servers instances may be created and destroyed frequently.
Generating the SSH Key Pair
On any machine (Windows, Linux, MacOS ...doesn't matter) generate an SSH key pair. Use this article as guide:
GitHub: Generating a new SSH key and adding it to the ssh-agent (you can skip the section "Adding your SSH key to the ssh-agent")
On the Target Server
On the target server, you will need to place the content of the public key (id_rsa.pub per the above article) into the .ssh/authorized_keys file under the home directory of the user which Jenkins will be using for deployment.
In Jenkins
Using "Publish over SSH" Plugin
Ref: https://plugins.jenkins.io/publish-over-ssh/
Visit: Jenkins > Manage Jenkins > Configure System > Publish over SSH
If the private key is encrypted, then you will need to enter the passphrase for the key into the "Passphrase" field, otherwise leave it alone.
Leave the "Path to key" field empty as this will be ignored anyway when you use a pasted key (next step)
Copy and paste the contents of the private key (id_rsa per the above article) into the "Key" field
Under "SSH Servers", "Add" a new server configuration for your target server.
Using Stored Global Credentials
Visit: Jenkins > Credentials > System > Global credentials (unrestricted) > Add Credentials
Kind: "SSH Username with private key"
Scope: "Global"
ID: [CREAT A UNIQUE ID FOR THIS KEY]
Description: [optionally, enter a decription]
Username: [USERNAME JENKINS WILL USE TO CONNECT TO REMOTE SERVER]
Private Key: [select "Enter directly"]
Key: [paste the contents of the private key (id_rsa per the above article)]
Passphrase: [enter the passphrase for the key, or leave it blank if the key is not encrypted]

Answer 3

For Windows:
Install the necessary plugins for the repository (ex: GitHub install GitHub and GitHub Authentication plugins) in Jenkins.
You can generate a key with Putty key generator, or by running the following command in git bash: $ ssh-keygen -t rsa -b 4096 -C your_email#example.com
Private key must be OpenSSH. You can convert your private key to OpenSSH in putty key generator
SSH keys come in pairs, public and private. Public keys are inserted in the repository to be cloned. Private keys are saved as credentials in Jenkins
You need to copy the SSH URL not the HTTPS to work with ssh keys.

Answer 4

Username it takes is "jenkins" while setting up the key credentials,
and then we need to switch to that user (in cli) in order to generate
key pair to make git connection work.
here are the steps
switch to jenkins user
sudo su - jenkins -s /bin/bash
Generate key pair
ssh-keygen
Configure private key in jenkins as described
Configure public key on git repository side in deploy key section
Test connection, it should work.
Note: This steps are for jenkins in local machine , ubuntu 20.04.