Allow for a decorator phase / command to i.e. force-tag alerts

[frittentheke]

Thanks for this very helpful tool!

I'd love to be able to define a decorator that applies changes to the collected data from configmaps before feeding it to i.e. Alertmanager or Grafana.

One very distinct use-case are Prometheus' alert definitions which are collected from multiple Kubernetes namespaces. If one wants to route the alerts based on the source namespace the configmap was picked-up from, this metadata needs to be immutably available. In case of alerts this requires the source to either ensure the PromQL query leaves this as label on the data or have it set an additional label or an annotations containing the namespace for each and every alert. Ensuring this over hundreds of alerts and many different teams and people without maintaining the source namespace info for each alert behind the scenes is prone to fail.

My suggestion is to simply allow a command to run for each configmap collected by trovilo which then receives the Kubernetes metadata of the individual configmap as environment variables, i.e. K8S_METADATA_NAMESPACE, K8S_METADATA_NAME. The command could simply be a call of sed or maybe even a jsonpatch which decorates the source data with additional info.

Running this arbitrary command and simply providing some variables to it does not make trovilo any more domain specific.
But especially in multi-tenancy the namespace might just be the most important piece of information one wants to add / keep on the data that is then given to Alertmanager or Grafana.

[arnisoph]

I can see your use case and the need for post-processing the files.

Actually this is partly already possible by defining a verify cmd that uses the file path (https://github.com/inovex/trovilo/blob/master/configmap/configmap.go#L16) to get the k8s namespace and the name of the file of the configmap. However this will only work as long as no underscores are used in namespaces/configmap.