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CircleCI Webhooks

TL;DR

To integrate CircleCI webhooks with ngrok:

  1. Launch your local webhook. npm start
  2. Launch ngrok. ngrok http 3000
  3. Configure CircleCI webhooks with your ngrok URL.
  4. Secure your webhook requests with verification.

This guide covers how to use ngrok to integrate your localhost app with CircleCI by using Webhooks. CircleCI webhooks can be used to notify an external application whenever specific events occur in your CircleCI account.

By integrating ngrok with CircleCI, you can:

  • Develop and test CircleCI webhooks locally, eliminating the time in deploying your development code to a public environment and setting it up in HTTPS.
  • Inspect and troubleshoot requests from CircleCI in real-time via the inspection UI and API.
  • Modify and Replay CircleCI Webhook requests with a single click and without spending time reproducing events manually in your CircleCI account.
  • Secure your app with CircleCI validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

Step 1: Start your app​

For this tutorial, we'll use the sample NodeJS app available on GitHub.

To install this sample, run the following commands in a terminal:

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This will get the project installed locally.

Now you can launch the app by running the following command:

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The app runs by default on port 3000.

You can validate that the app is up and running by visiting http://localhost:3000. The application logs request headers and body in the terminal and responds with a message in the browser.

Step 2: Launch ngrok​

Once your app is running successfully on localhost, let's get it on the internet securely using ngrok!

  1. If you're not an ngrok user yet, just sign up for ngrok for free.

  2. Download the ngrok agent.

  3. Go to the ngrok dashboard and copy your Authtoken.
    Tip: The ngrok agent uses the auth token to log into your account when you start a tunnel.

  4. Start ngrok by running the following command:

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  5. ngrok will display a URL where your localhost application is exposed to the internet (copy this URL for use with CircleCI). ngrok agent running

Step 3: Integrate CircleCI​

To register a webhook on your CircleCI account follow the instructions below:

  1. Access CircleCI and sign in using your CircleCI account.

  2. On the All Pipelines page, click the name of your pipeline. Tip: If you don't have one, create a new pipeline.

  3. On your pipeline page, click Project Settings and then click Webhooks on the left menu.

  4. On the Webhooks page, click Add Webhook.

  5. On the Add Webhook page, enter a name in the Webhook name field, and in the Receiver URL field enter the URL provided by the ngrok agent to expose your application to the internet (i.e. https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app). URL to Publish

  6. Enter MySecretToken in the Secret token field, click the Workflow Completed and Job Completed checkboxes under Events, and then click Add Webhook.

  7. On the Webhooks page, click the name of your webhook, and then click Test Ping Event.

    Confirm your localhost app receives the test-ping event notification and logs both headers and body to the terminal.

Run Webhooks with CircleCI and ngrok​

You can trigger new calls from CircleCI to your application by following the instructions below.

  1. Access CircleCI and sign in using your CircleCI account. Tip: If you are at the Project Settings page, click < at the top left corner to return to your pipeline page.

  2. On the Pipeline page, click Rerun workflow from start under the Action column for your pipeline.

    Confirm your localhost app receives event notifications related to the workflow you started and logs both headers and body in the terminal.

Inspecting requests​

ngrok's Traffic Inspector captures all requests made through your ngrok endpoint to your localhost app. Click on any request to view detailed information about both the request and response.

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By default, accounts only collect traffic metadata to avoid exposing secrets. You must enable full capture in the Observability section of your account settings to capture complete request and response data.

Use the traffic inspector to:

  • Validate webhook payloads and response data
  • Debug request headers, methods, and status codes
  • Troubleshoot integration issues without adding logging to your app

Replaying requests​

Test your webhook handling code without triggering new events from your service using the Traffic Inspector's replay feature:

  1. Send a test webhook from your service to generate traffic in your Traffic Inspector.

  2. Select the request you want to replay in the traffic inspector.

  3. Choose your replay option:

    • Click Replay to send the exact same request again
    • Select Replay with modifications to edit the request before sending

  4. Modify the request (optional): Edit any part of the original request, such as changing field values in the request body.

  5. Send the request by clicking Replay.

Your local application will receive the replayed request and log the data to the terminal.

Secure webhook requests​

The ngrok signature webhook verification feature allows ngrok to assert that requests from your CircleCI webhook are the only traffic allowed to make calls to your localhost app.

Note: This ngrok feature is limited to 500 validations per month on free ngrok accounts. For unlimited, upgrade to Pro or Enterprise.

This is a quick step to add extra protection to your application.

  1. Create a file named circleci_policy.yml, replacing {your secret token} with the value you have provided to the Secret token field during your webhook registration (See Integrate ngrok and CircleCI):

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  2. Restart your ngrok agent by running the command:

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  3. Access CircleCI and Rerun your workflow from start.

    Verify that your local application receives the request and logs information to the terminal.