Deploy a custom metrics script in the sidecar

A custom Lua script can be added to the redis-exporter sidecar by way of the metrics.extraArgs.script parameter. The pathname of the script MUST exist on the container, or the redis_exporter process (and therefore the whole pod) will refuse to start. The script can be provided to the sidecar containers via the metrics.extraVolumes and metrics.extraVolumeMounts parameters:

metrics:
  extraVolumeMounts:
    - name: '{{ printf "%s-metrics-script-file" (include "common.names.fullname" .) }}'
      mountPath: '{{ printf "/mnt/%s/" (include "common.names.name" .) }}'
      readOnly: true
  extraVolumes:
    - name: '{{ printf "%s-metrics-script-file" (include "common.names.fullname" .) }}'
      configMap:
        name: '{{ printf "%s-metrics-script" (include "common.names.fullname" .) }}'
  extraArgs:
    script: '{{ printf "/mnt/%s/my_custom_metrics.lua" (include "common.names.name" .) }}'

Then deploy the script into the correct location via extraDeploy:

extraDeploy:
  - apiVersion: v1
    kind: ConfigMap
    metadata:
      name: '{{ printf "%s-metrics-script" (include "common.names.fullname" .) }}'
    data:
      my_custom_metrics.lua: |
        -- LUA SCRIPT CODE HERE, e.g.,
        return {'bitnami_makes_the_best_charts', '1'}