Support optional ConfigMap volumes for alerting rules

[sl4dy]

Proposal

Support optional ConfigMap volumes for alerting rules

We provide ConfigMaps with alerting rules in Helm chart of particular application. However, we need to make Prometheus aware of such ConfigMaps prior to creating the particular Helm chart containing the given ConfigMap. I have tried to mark the ConfigMap volume as optional:

      volumes:
        - name: prometheus-config-volume
          configMap:
            name: prometheus-server-conf
        - name: rules-volume
          configMap:
            name: prometheus-rules
        - name: component-rules-volume
          configMap:
            name: component-rules
            optional: true

However Prometheus fails to start:

level=error ts=2018-07-25T09:56:53.963527236Z caller=manager.go:479 component="rule manager" msg="loading groups failed" err="read /etc/prometheus-rules/vertica-monitoring-rules.yaml: is a directory" level=error ts=2018-07-25T09:56:53.963723232Z caller=main.go:607 msg="Failed to apply configuration" err="error loading rules, previous rule set restored"

It would be great if Prometheus can ignore the file if it is directory - caused by the optional parameter in the volume.

[simonpasquier]

In general the project prefers to fail hard on configuration errors (such as using a directory where the application expects a file) rather than silently catching the error and expecting the user to notice it.

[sl4dy]

Understood, but the optional volume is a great feature which cannot be used right now. Anyway, I get your point and I have handled the situation by ensuring that the rules configMap shall exist before mounting it.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.