k8s-job-webhooks

k8s-job-webhooks is a Kubernetes client application built with Rust that monitors Kubernetes Jobs and triggers webhooks upon Job completion.

The application exposes an HTTP server and REST endpoints built with Actix Web, allowing users to create webhooks that are triggered upon the completion of specific Jobs.

This project is currently in development.

REST endpoints

You can find the OpenAPI specification in the project directory.

• POST /webhooks
• GET /webhooks
• POST /job-done-watchers
• GET /job-done-watchers/{id}
• GET /job-done-watchers

How to use it

Before using k8s-job-webhooks, you need to create at least one webhook using the POST /webhooks endpoint.

Once a webhook is created, you need to create a Job Done Watcher (observer completion Job). The best way to automate this process is by using init containers within your Kubernetes Jobs.

To observe a Job for its completion, you must create a Job Done Watcher using the POST /job-done-watchers endpoint. The request body requires the Job name and the webhook ID (obtained earlier). The Job name can easily be injected into the init container using Kubernetes' downward API via environment variable.

Here is an example of a Kubernetes Job definition with an init container that registers a Job Done Watcher automatically: The best way to use k8s-job-webhooks is to create Kubernetes jobs that include init containers to register webhooks. Here is an example of a job definition:

apiVersion: batch/v1
kind: Job
metadata:
  name: example-job
spec:
  template:
    spec:
      initContainers:
        - name: init-http-request
          image: busybox
          env:
            - name: JOB_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.labels['job-name']
          command:
            - "sh"
            - "-c"
            - |
              requestBody='{
                  "jobName": "$JOB_NAME",
                  "jobDoneTriggerWebhooks": [
                    {
                      "webhookId": "bb8d54c0-42f0-4d96-9e50-151645693a94"
                    }
                  ]
              }'

              requestBody=$(echo $requestBody | sed "s/\$JOB_NAME/$JOB_NAME/")

              wget --header="Content-Type: application/json" \
                --post-data="$requestBody" \
                http://k8s-job-webhook-service:8080/job-done-watchers
      containers:
        - name: example-container
          image: busybox
          command: ["printenv"]
      restartPolicy: Never
  backoffLimit: 4

Using CronJob

The procedure for using CronJobs is quite similar to that for Jobs. However, since a CronJob may create multiple Pods for the same Job, it’s important to avoid creating the same Job Done Watcher multiple times, which would result in multiple webhook invocations upon Job completion. To prevent this, the POST /job-done-watchers endpoint allows you to specify an Idempotency-Key HTTP header, making the request idempotent.

Here’s an example of a CronJob definition:

apiVersion: batch/v1
kind: CronJob
metadata:
  name: example-cronjob
spec:
  schedule: "*/1 * * * *" 
  jobTemplate:
    spec:
      parallelism: 2 # => two init containers
      completions: 2  
      template:
        spec:
          initContainers:
            - name: init-http-request
              image: busybox
              env:
                - name: JOB_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.labels['job-name']
              command:
                - "sh"
                - "-c"
                - |
                  requestBody='{
                      "jobName": "$JOB_NAME",
                      "jobDoneTriggerWebhooks": [
                        {
                          "webhookId": "bb8d54c0-42f0-4d96-9e50-151645693a94",
                          "timeoutSeconds": 0
                        }
                      ]
                  }'

                  requestBody=$(echo $requestBody | sed "s/\$JOB_NAME/$JOB_NAME/")

                  wget --header="Content-Type: application/json" \
                    --header="Idempotency-Key: $JOB_NAME" \
                    --post-data="$requestBody" \
                    http://k8s-job-webhook-service:8080/job-done-watchers
          containers:
            - name: echo-container
              image: busybox
              command: ["printenv"]
          restartPolicy: OnFailure

Job Labeling

The completed Job will be labeled with the label app.k8s.job.webhooks/webhooks-called set to true.