Multiple Deploy Keys and Jenkins

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Jenkins Multiple Deploy Keys and Github Hooks

The other day I ran into an annoying issue. And it's such common one that github has a page for it. I was setting up an application for continous integration. The common components were there. Application, Jenkins, and a VCS, and there I was with an error. The issue is that you can't have a deploy key in use by multiple repositories. Github suggests using machine users but that's a bit of a pain in my opinion. As I rather manage everything from the server.

Multiple SSH Keys and Jenkins

So the way around this is to setup a deploy key for each project. This is easily done with the command:

ssh-keygen -t rsa -f <filename>

Since these are keys that will be used by machines, you'll want to leave the password blank or you'll get some annoying issues to deal with later. So, with that in mind become your jenkins user and create one!

su jenkins #login as jenkins
cd #change to jenkins's home directory
ssh-keygen -t rsa -f .ssh/id_rsa_myreponame    

Next we'll do the "magic" here, open up your SSH configuration file like so vi .ssh/config and enter:

Host myrepo
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_myreponame

Now that that's in place you can test the connection:

ssh -T myrepo

And you'll get back the usual "You've successfully authenticated, but GitHub does not provide shell access." So you're halfway there. The next thing you should do is go to your Jenkins server, the job configuration you're working on, and update the github urls to use your new host. For example, if you're using the Github Plugin for jenkins you'll update the Github project area to say: myrepo/username/repository/. And if you're using the Git plugin you'll update the Source Code Management -> Repository URL area to say: myrepo/username/repo.git and set the credentials area to use the ssh file you just made.

Once you do that and add the SSH key as a deploy key to github, you're done if you just want to have the one jenkins server talk to multiple github projects. But wait, there's more!

What about continous integration?

When it comes to the Github Jenkins Plugin, you're out of luck as far as I know. Because the /github-plugin hook, is sent the Github version of the url in the post data. You'll see nice errors like this in your logfile:

INFO: Received POST for https://github.com/username/repo
Aug 21, 2015 1:53:25 PM com.cloudbees.jenkins.GitHubRepositoryName create
WARNING: Could not match URL myrepo:username/repo.git
Aug 21, 2015 1:53:25 PM com.cloudbees.jenkins.GitHubWebHook processGitHubPayload
INFO: Poked Specification Build

But, if you're using the git plugin you're in luck because the push notification takes a url= parameter that you can use to specify your customized url in. The useful thing (and I'm not sure if it's supposed to do this, but it does) is this endpoint responds to both GET and POST requests the same way. So you can go to your github repository settings and add a WebHook with the specified url:

http://yourserver/git/notifyCommit?url=<URL of the Git repository>

To the Jenkins Hook URL field in the settings for the jenkins web hooks. And then you should see builds when you push to your repository!

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