Jenkins Docker and Gitlab

on jenkins, gitlab, ssh, docker

In this blog post I will explain how I configured my Jenkins (running in a docker container) to be able to clone and push on a private Gitlab git repository.

I assume that you have docker and jenkins already installed and running

Create and get the Jenkins key

First get the name (or the ID) of the Jenkins Container :

In a terminal type :

docker ps | grep jenkins

This should return something like that :

CONTAINER ID        IMAGE                 COMMAND                  CREATED             STATUS              PORTS                                              NAMES
f26fa8c9bef9        jenkins/jenkins:lts   "/bin/tini -- /usr..."   41 hours ago        Up 41 hours         0.0.0.0:8080->8080/tcp, 0.0.0.0:50000->50000/tcp   jenkins

The ID is f26fa8c9bef9 (from first column) and the name is jenkins (from last column).

Then "enter" the container in order to create the SSH key :

docker exec -it jenkins /bin/bash
You need to adapt the name (jenkins) with the container ID or your name.

So now you the terminal prompt should have changed :

jenkins@f26fa8c9bef9:/$

Check if you already have an ssh key :

cat ~/.ssh/id_rsa.pub

If you have something else than cat: /var/jenkins_home/.ssh/id_rsa.pup: No such file or directory then you already have the key so you can directly go to the section <Add your credentials to jenkins>

To create the key execute the following command :

ssh-keygen

And do not use passphrase and accept default values :

Generating public/private rsa key pair.
Enter file in which to save the key (/var/jenkins_home/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /var/jenkins_home/.ssh/id_rsa.
Your public key has been saved in /var/jenkins_home/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:MNSY7yiVerfBoYR0vCZZeS9n73cevZJl/ezUoSZcoj8 jenkins@f26fa8c9bef9
The key's randomart image is:
+---[RSA 2048]----+
|     ..=         |
|    ..B o        |
|   . =o= .       |
|    + *o+ +      |
|     * =S= o . ..|
|    o + = o + .o=|
|     o . + + o+o=|
|        . .E+o..*|
|           ....=o|
+----[SHA256]-----+

Then get your public key, by copy / paste the ouptut of this command :

cat ~/.ssh/id_rsa.pub

You should have something like that

jenkins@f26fa8c9:/$ cat ~/.ssh/id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDN6y54DIbEDp2gAgyu8ApzJ/tvxSu6myAkEQL3eUiLiLr5YC+uOalJ4AHkWwlmDWoT6SzlpvR+CQD2xEvsHoEumgTuUn1sNNVisIsyd19ga5yqBobM2/zhAaKtpkkuY9k1wOAZERsEIRm4Q5YTvVjNfIug/ZxVzg0xqJc0w9NGGuKNwOlBaCfjyJrhwdGU79Ijoq8sJ8SuswHc2DzvJWgdfXXd1T7w+NdOKqR+yzF5UXIm2uP6x/rVJ6OuINjFY0ODIkLvJtyvaHsIGAJZP21mJlJRPx18vAr6Phy+YmW2+UgEi2I6jxcQ+DYDT3TbTO+qpc+7KOLnRZyQKwnNu1T jenkins@f26fa8c9

Add your credentials to jenkins

Now you created your SSH key so you can create the Credential.

Go to your jenkins, log in, and and click on left menu item "Credentials", then sub item "System", Select "Global Credentials (unrestricted)"

jenkins global credentials.png

Then click on "Add Credentials" in left menu.

And fill the form as this :

jenkins add credentials.png

  • Kind : SSH Username with private key

  • Scope : Global (Jenkins, nodes, items, all …​)

  • Username : git

  • Private Key : From the Jenkins master ~/.ssh

  • Passphrase : empty (or your pass phrase if you have one)

  • ID : empty

  • Description : The Jenkins SSH KEy (or whatever you want)

Then Save.

Add your key to Gitlab

Now you have your ssh key, so go to your gitlab project you want to build with Jenkins, and click on "Settings", then "Repository".

gitlab settings repository deploy keys.png

  • Title : Jenkins (Or anything else)

  • Key : your public key (the output of the command cat ~/.ssh/id_rsa.pub)

You can check the Write access allowed if you need it.

Then save.

Create a jenkins job

Now, in Jenkins, you can create a job that use your repository, just remember to use the "SSH" version of your repository url :

jenkins job pipeline credentials.png

And it should be able to clone !

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