Architecture Note: Configuring Read the Docs Webhook-Triggered Builds

The Problem: Synchronizing Docs with Code Pushes

Manual documentation builds create a lag between code changes and updated guides, leading to outdated documentation. The goal is to automate the build trigger using a webhook—a user-defined HTTP callback—that notifies Read the Docs (RTD) immediately upon a Git push.

Requirements

To implement automated triggers, the following components must be in place:

• Git Repository: A public or private repository on a host supporting webhooks (e.g., GitHub, GitLab, Bitbucket).
• Linked RTD Project: A project already configured in Read the Docs and linked to the source repository.
• API Token: An RTD API token with build scope permissions to authorize the build request.
• Administrative Access: Permissions to modify webhook settings on the repository host.

Smallest Suitable Design

The most efficient design avoids complex middleware and uses a direct POST request from the repository host to the Read the Docs API. When a push event occurs, the host sends a payload to the following endpoint:

https://readthedocs.org/api/v2/webhook/<project-id>/<webhook-id>/

The design relies on a shared secret. The repository host includes this secret in the request header or payload; RTD validates the secret before initiating a build of the default version. This ensures that only authorized pushes trigger resource-intensive build processes.

Trust and Data Boundaries

Security is maintained by isolating secrets from the source code:

• Webhook Secret: This high-entropy string (minimum 32 bytes recommended) exists only in the repository host's webhook settings and the RTD project configuration. It must never be committed to the Git repository.
• API Token: Stored securely within RTD's internal environment. It is not exposed to the repository host.
• Access Control: Only repository administrators can modify the webhook URL or secret, preventing unauthorized users from triggering builds or intercepting the secret.

Operational Checks

To ensure the pipeline is healthy, monitor these specific indicators:

Check	Expected Result	Diagnostic Location
Delivery Status	HTTP 2xx Response	Repository Host Webhook Logs
Trigger Source	Listed as "webhook"	RTD Build History
Commit Alignment	Build SHA matches Push SHA	RTD Build Logs

Enable automatic retries on the repository host to handle transient network timeouts during the POST request.

Failure Modes and Design Changes

Several conditions can break the automation or necessitate a more complex architecture:

• Secret Mismatch: If the secret is rotated on one end but not the other, RTD will return an HTTP 401 Unauthorized. No build will start.
• Token Revocation: If the API token expires, the webhook may be acknowledged (2xx), but the build will fail to queue.
• Rate Limiting: High-frequency pushes may trigger rate limits on the repository host or hit RTD's concurrency limits, causing queued builds to delay.
• Private Repo Complexity: If the repository requires specific SSH keys or a custom build environment not handled by the standard integration, the design must be extended to include a readthedocs.yml configuration file.

Verification Procedure

Run these steps to verify the implementation. Note: These steps should be performed in a test repository to avoid disrupting production docs.

1. Positive Test: Push a small change to the default branch. Check the repository host's delivery log for a 200-series response and verify the RTD build list shows a "webhook" trigger.
2. Negative Test: Temporarily change the secret in the repository host to an incorrect value. Push a change and verify that RTD returns an HTTP 401 and no build is initiated.
3. Rotation Test: Generate a new secret and API token. Update both the host and RTD settings, then push a change to ensure the system recovers after a credential rotation.