CargoXio / k8s-map-updater

Use templating to update maps when pods change

Update map when pods change

This is a really simple container that changes the contents of the map if the pods are created, updated or deleted.

Why

This was done merely for the need of Redis HAProxy:

• the proxy needs a configuration file (haproxy.cfg),
• the configuration file needs to include a list of all the pods where redis is running
• pods do not have a DNS name and can only be accessed through a Service (which connects to any of the available pods) or directly by IP address,
• IP addresses change if the pods are restarted, added or removed and then it's game over.

Henceforth, the configuration might become invalid if the pods are restarted and would need to be recreated.

How

1. This simple tool watches for changes to the Pods in its namespace. Whenever a pod is added, removed or updated, a trigger is fired.
2. As a convenience, the trigger will fire if the template file is changed, as well, giving you an option to live update the template without restarting the service.
3. The trigger will take the supplied template, pass in the {{ .pods }} configuration and create a new configuration.
4. It will update the configured ConfigMap with new configuration file.
5. It is up to the user (e.g. through pod annotation with reloader) to restart ha-proxy when this configuration is changed.