Webcheck Docker Container

This Docker container acts as a URL check mechanism for container orchestration systems. The container is meant to be run as Kubernetes job. Once activated, the image will perform basic GET requests to a URL and exit with a return code of zero if a series of successful responses are received.

This container is configured via the use of the following environment variables.

• INTERVAL: How frequently (in seconds) do we run a check
• COUNT: Number of checks to run. If set to value greater than zero, DURATION is ignored
• MAX_DURATION: Set max duration to limit check script to a specific duration if COUNT is used
• DURATION: How long (in seconds) does the job run if COUNT is not used
• FAILURE_LIMIT: How many failures the check script is willing to tolerate before exiting with a non-zero return code
• URL: The URL to check
• JQ_PARSER: The jq string used by the check script to extract information from the checked URL response.
• EXPECTED_RESPONSE: The expected string to compare against after applying the JQ_PARSER
• TIMEOUT: The timeout setting for curl to use when making requests
• DEBUG: Set this to enable debug output

Caveats related to the check script that is run within this container.

• COUNT and DURATION variables are mutually exclusive
• Checked URLs should provide a response in JSON format
• The check script will exit with a non-zero return code when FAILURE_LIMIT has been reached

A good reference for setting environments variables for containers can be found at the following link.

Define Environment Variables for a Container

This container was built to accompany a blog post related to using Argo Rollouts to revert failed Kubernetes deployments. Please reference the following link for more specifics on how it is used.

Exploring GitOps with Argo Part 2

An example of a job that utlizes this container looks like the following.

apiVersion: batch/v1
kind: Job
metadata:
  name: rollout-webcheck-job
spec:
  backoffLimit: 0
  template:
    metadata:
      name: rollout-webcheck-job
    spec:
      restartPolicy: Never
      containers:
      - name: webcheck
        image: public.ecr.aws/i4a3l2a7/webcheck:latest
        env:
        - name: URL
          value: 'http://192.168.0.161:30090/healthz'
        - name: INTERVAL
          value: '5'
        - name: DURATION
          value: '300'
        - name: FAILURE_LIMIT
          value: '5'
        - name: JQ_PARSER
          value: '.status'
        - name: EXPECTED_RESPONSE
          value: 'ok'
        - name: TIMEOUT
          value: '3'