Demo Build Triggers

Welcome — this lesson covers how to automatically trigger OpenShift builds using GitLab webhooks. We’ll assume you already have a BuildConfig configured with the Docker build strategy and that the build source is a Git repository (hosted in GitLab for this demo). When you push code changes to the repository, OpenShift can start builds automatically via webhooks instead of requiring manual starts.

Example application change

Here is a small Flask app update you might push to demonstrate an automatic build trigger:

import os
from flask import Flask
app = Flask(__name__)

@app.route("/")
def main():
    return "Welcome! Update 1"

@app.route("/how are you")
def hello():
    return "I am good, how about you?"

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=8080)

Manual build (quick reminder)

To start a build manually from the OpenShift web console: open your BuildConfig and click Start Build. The build details will indicate it was triggered manually.

Set up GitLab webhook to trigger builds automatically

OpenShift BuildConfig objects include a triggers section with several webhook options: a generic webhook, a GitHub webhook, and the ability to add GitLab or Bitbucket webhooks. To configure GitLab to notify OpenShift when you push code, follow these steps:

In the BuildConfig view in the OpenShift console, go to Actions → Edit.
Under Triggers, click Add Webhook and select GitLab as the webhook type.
You must use a webhook secret to secure the webhook. If you don’t have one, click Create New Webhook to generate a secret for GitLab, then create it.

A screenshot of the OpenShift Origin web console showing a "Create Webhook Secret" dialog over the Builds settings. The modal contains fields for "Secret Name" and "Webhook Secret Key" with Cancel and Create buttons.

Select the newly created webhook and save the BuildConfig. The GitLab webhook URL will now appear in the BuildConfig Triggers section — copy that URL.
In your GitLab project, go to Settings → Integrations (or Webhooks) and paste the webhook URL into the URL field. The secret token is embedded in the URL, so you do not need to enter a separate token.
For local development without a valid SSL certificate, uncheck Enable SSL verification before saving the webhook.
Save the webhook and use the Test button to verify the connection.

Tip: The webhook URL includes the secret token, so keep it private. For production environments, leave SSL verification enabled and secure the webhook URL.

Troubleshooting: GitLab blocks requests to the local network

If you test the webhook from a GitLab instance that blocks outbound requests to local network addresses (common in local development), you may see an error in the GitLab logs indicating requests to local network addresses are blocked. Example log excerpt:

==> /var/log/gitlab/gitlab-monitor/current <==
2018-04-30_10:42:15.04151 127.0.0.1 - - [30/Apr/2018:10:42:15 UTC] "GET /sidekiq HTTP/1.1" 200 12152

==> /var/log/gitlab/gitlab-rails/production.log <==
Started GET "/root/simple-webapp/hooks/2/test?trigger=push_events" for 192.168.56.1 at 2018-04-30 10:42:16 +0000
Processing by Projects::HooksController#test as HTML
  Parameters: {"trigger"=>"push_events", "namespace_id"=>"root", "project_id"=>"simple-webapp", "id"=>"2"}
Completed 500 Internal Server Error in 171ms (ActiveRecord: 3.4ms)

==> /var/log/gitlab/gitlab-rails/production_json.log <==
{"method":"GET","path":"/root/simple-webapp/hooks/2/test","format":"html","controller":"Projects::HooksController","action":"test","status":500,"error":"Gitlab::HTTP::BlockedUrlError: URL 'https://192.168.99.100:8443/oapi/v1/namespaces/my-webapplication/buildconfigs/simple-webapp-docker/webhooks/294583a58edeaed9/gitlab' is blocked: Requests to the local network are not allowed","duration":216.99,"view":0.0,"db":3.38,"time":"2018-04-30T10:42:16.785Z","params":[{"key":"trigger","value":"push_events"},{"key":"namespace_id","value":"root"},{"key":"project_id","value":"simple-webapp"},{"key":"id","value":"2"}],"remote_ip":"192.168.56.1","user_id":1,"username":"root","gitaly_calls":4}

Gitlab::HTTP::BlockedUrlError (URL 'https://192.168.99.100:8443/oapi/v1/namespaces/my-webapplication/buildconfigs/simple-webapp-docker/webhooks/294583a58edeaed9/gitlab' is blocked: Requests to the local network are not allowed):
  lib/gitlab/proxy_http_connection_adapter.rb:17:in `rescue in connection'
  lib/gitlab/proxy_http_connection_adapter.rb:14:in `connection'
  app/services/web_hook_service.rb:73:in `make_request'
  app/services/web_hook_service.rb:26:in `execute'
  app/models/hooks/web_hook.rb:10:in `execute'
  app/services/test_hooks/base_service.rb:22:in `block in execute'
  app/services/test_hooks/base_service.rb:19:in `catch'

Warning: For GitLab to reach a local OpenShift server, allow outbound requests to local network addresses in GitLab’s Admin Area. On the GitLab server go to Admin Area → Settings → Outbound requests and check Allow requests to the local network. Only enable this in trusted development environments.

After enabling that option in GitLab, retest the webhook in your project. Once the webhook test succeeds, pushes to the repository (or using the Test button) will trigger OpenShift builds automatically.

Verify the build in OpenShift

Back in the OpenShift console you can watch the build progress. When it finishes, open the build details to confirm the trigger type — the build record will indicate it was started by a GitLab webhook.

A screenshot of the OpenShift Origin web console showing the "My WebApplication" project and the build details for "simple-webapp-docker-4." The page shows build status as "Complete" along with configuration and source repository information.

Quick reference

Topic	Recommendation
Webhook types available	Generic, GitHub, GitLab, Bitbucket (configure under BuildConfig → Triggers)
Webhook secret	Create via Create New Webhook in the BuildConfig editor; token is embedded in the webhook URL
Local dev SSL	Uncheck Enable SSL verification in GitLab webhooks for local testing only
GitLab local requests blocked?	Enable Allow requests to the local network in GitLab Admin Area for trusted dev setups

Links and references

OpenShift Builds and BuildConfig concepts: https://docs.openshift.com/
GitLab Webhooks documentation: https://docs.gitlab.com/ee/user/project/integrations/webhooks.html
GitLab Admin settings for outbound requests: https://docs.gitlab.com/ee/administration/settings/outbound_requests.html

That’s it — you now have GitLab configured to trigger OpenShift builds automatically when repository changes are pushed.

Introduction

Pre-Requisite - Docker and Kubernetes

Getting Started with OpenShift

OpenShift Concepts - Projects and Users

Concepts - Builds and Deployments

Networks, Services, Routes and Scaling

Storage, Templates and Catalog

Conclusion and APPENDIX

Demo Build Triggers

Example application change

Manual build (quick reminder)

Set up GitLab webhook to trigger builds automatically

Troubleshooting: GitLab blocks requests to the local network

Verify the build in OpenShift

Quick reference

Links and references

Watch Video

​Example application change

​Manual build (quick reminder)

​Set up GitLab webhook to trigger builds automatically

​Troubleshooting: GitLab blocks requests to the local network

​Verify the build in OpenShift

​Quick reference

​Links and references

Watch Video

Example application change

Manual build (quick reminder)

Set up GitLab webhook to trigger builds automatically

Troubleshooting: GitLab blocks requests to the local network

Verify the build in OpenShift

Quick reference

Links and references