Receive Github webhooks on Jenkins without public IP

Nov 23, 2017, by Karolis Rusenas

github jenkins tutorial webhooks

Jenkins is probably the most popular CI tool. Since Dev and Ops roles are growing more and more alike we need to reduce initially required ‘activation energy’ to adopt automation tools. Building and testing software should be easy, fast and reliable. Current technique known as polling repository usually results in constant delays where engineers have to wait till the next CI scanning cycle.

Another option is to use webhooks but that requires you to expose your CI server to the public internet (you can still whitelist IPs though).

In this article we are going to show how to configure end-to-end CI pipeline where you can instantly
trigger jobs via Webhook Relay service without internal Jenkins being exposed to public internet.

Desired workflow

Let’s say we need to connect GitHub with internally deployed Jenkins which is not reachable from outside. In order to do this, we will be using Webhook Relay:

desired workflow

Once webhook is relayed by the agent, Jenkins pulls the newest code and executes the configured job.

Step 1: Create GitHub repository

First things first, we need to get a repository! If you haven’t got GitHub account, get one.
You will need it later to login to Webhook Relay too.
Once you have logged into GitHub, look for a green “New Repository” button on the bottom right corner and click it.

creating new github repo

Choose public option as it will make this tutorial slightly quicker. Don’t close this repo window as we will be back there shortly.

Step 2: Jenkins Installation (if you already have it - ignore this step)

It’s time to get that Jenkins up and running! Head to https://jenkins.io/download/ and download our beloved (it’s not pretty but gets the job done) Jenkins. In this guide we use standard installation but I would recommend using dockerized images, especially since it’s so easy to build a new image on top of the official one.

Step 3: Setting up Jenkins with Github-Plugin

The easiest way to start receiving GitHub webhooks is by using this plugin https://plugins.jenkins.io/github:

manage jenkins


Add default GitHub server (don’t bother adding credentials as we are using public repo anyway):

jenkins add gh


Step 4: Configuring Jenkins Job

When you want Jenkins to do something - create a job. In this case we will be using Freestyle project:

jenkins create job


We have to configure several sections here - Source Code Management and Build Triggers. First, set repository (in this case it’s my demo app repo repository):

jenkins create job


Next step is setting a build trigger to GitHub hook trigger for GITScm polling:

jenkins build trigger


This means that once the Jenkins receives a webhook, it can identify which repo is changed and thus triggers a pull and job execution.

Step 5: Configuring Webhook Relay

First of all you will have to register and download the agent. See installation instructions if you don’t have an account yet (you can use GitHub OAuth option since you would already have an account with it).

For authentication, agents use pairs of keys and secrets or regular account usernames/passwords. Head to the tokens page (left navigation menu) and create one key/secret pair. Be sure to copy those somewhere so you don’t lose them in the next 2 minutes.

Step 6: Setting up Webhook Relay agent

To login with the CLI use token (generate it here) key/secret:

relay login -k your-token-key -s your-token-secret

You will then need to start forwarding webhooks to Jenkins:

relay forward --bucket github-jenkins http://localhost:8080/github-webhook/
Forwarding:
https://my.webhookrelay.com/v1/webhooks/6edf55c7-e774-46f8-a058-f4d9c527a6a7 -> http://localhost:8080/github-webhook/
Starting webhook relay agent...
1.511438424864371e+09 info webhook relay ready... {"host": "api.webhookrelay.com:8080"}

Once you have your Input URL (in this case it’s https://my.webhookrelay.com/v1/webhooks/6edf55c7-e774-46f8-a058-f4d9c527a6a7) get back to GitHub’s webhook configuration and set it:

github webhook config

That’s it! The agent is running and forwarding requests.

Create sample application

For the sake of demo I have created a sample application, source code here. It has some tests inside that our Jenkins job will be able to run. I use EnvInject Plugin to provide access to system’s Go. The last thing left, is to add build step:

jenkins build

On the Webhook Relay logs page https://my.webhookrelay.com/logs you should be a able to see sent logs.

Test it!

Now, do some changes and push to master. In a few seconds you should see that Jenkins is checking repository. Cheers!

Wrapping it up

Webhooks are not a new thing. A lot of public services use them to notify one another about certain events. The tricky part, however, is when you need them during development or when you have services that are not accessible through the public internet.
That’s where Webhook Relay offers a straight forward solution to the problem.