Unified webhook endpoint

Last weekend I finally wanted to invest the time to automatically deploy zerokspot.com whenever there was a change in its source repository. Up until then, I basically had to open my laptop and execute a simple deployment script to build all the pages using Hugo and update the search index with the latest content.

What I ended up doing was to first put the repository onto Gitlab in order to integrate their CI/CD system. I didn’t want to give Gitlab SSH access to my primary webserver, though, so I decided to look into what webhooks Gitlab offered to notify my server that there was a new build to be deployed. Turns out, there is a collection of pipeline events, one for every state of a pipeline. (I only cared about the with status=success.)

Next, I started implementing my own little HTTP endpoint that would do the actual deployment once it got called with the right secret. It should download all the artefacts created by the pipeline, move them into the right folders, and restart the search server.

Luckily, I stumbled upon Adnan Hajdarević’s webhook project, which already does the first part in a generic fashion. It allows you to define endpoints for your webhooks, filter calls against those endpoint for matching attributes (within the body, URL, or HTTP header), and call an executable.

The whole configuration can be put into a simple JSON or YAML file (I don’t like JSON for configuration files, so YAML it is…), which looked somehow like this for my setup:

---
- id: "zerokspot"
  execute-command: "/path/to/script.sh"
  command-working-directory: "/working/dir/"
  pass-arguments-to-command:
    - source: string
      name: "--access-token"
    - source: string
      name: "<GITLAB API TOKEN>"
  pass-file-to-command:
    - source: entire-payload
      name: payload
  trigger-rule:
    and:
      - match:
          type: value
          value: pipeline
          parameter:
            source: payload
            name: "object_kind"
      - match:
          type: value
          value: success
          parameter:
            source: payload
            name: object_attributes.status
      - match:
          type: "value"
          value: "<GITLAB SECRET>"
          parameter:
            source: "header"
            name: "X-Gitlab-Token"

Here I’ve defined a webhook for “zerokspot” (which means that it will be reachable on http://domain/hooks/zerokspot) and will trigger /path/to/script.sh but only if the request has the JSON properties object_kind=pipeline and object_attributes.status=success in its body/payload and <GITLAB SECRET> as the value of the X-Gitlab-Token header.

The last part still required a bit of custom coding in order to download the artefacts and move the around, but Adnan’s tool still helped a lot and thanks to it I could roll automated deployment of my site out last night 😃

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