loki.source.podlogs: Add option to keep discovered labels

[walnuss0815]

Background

Currently the discovered pod metadata labels (discovered_labels, see https://grafana.com/docs/alloy/latest/reference/components/loki/loki.source.podlogs/#podlogsspec) are only available in the RelabelConfig of the PodLogs CR. I would like to archive that the discovered labels/discovered_labels from loki.source.podlogs are available in a loki.relabel component, so I can relabel the logs without appending common relabeling rules to every PodLogs CR.

I've attached the current configuration below.

Alloy component graph: loki.source.podlogs --> loki.relabel --> loki.write

config.alloy

loki.source.podlogs "podlogs" {
  clustering {
    enabled = true
  }
  forward_to = [loki.relabel.podlogs.receiver]
}

loki.relabel "podlogs" {
  forward_to = [loki.write.local.receiver]
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_namespace"]
    target_label = "namespace"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_name"]
    target_label = "pod"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_container_name"]
    target_label = "container_name"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_node_name"]
    target_label = "node"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_label_app_kubernetes_io_instance"]
    target_label = "instance"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_label_app_kubernetes_io_name"]
    target_label = "app"
  }
}

loki.write "local" {
  endpoint {
    url = "http://loki-gateway.loki:80/loki/api/v1/push"
  }
}

example-podlogs.yaml

apiVersion: monitoring.grafana.com/v1alpha2
kind: PodLogs
metadata:
  name: example
  namespace: example
spec:
  selector: {}
  namespaceSelector:
    matchLabels:
      kubernetes.io/metadata.name: example

Proposal

I suggest to make it possible to keep discovered labels from loki.source.podlogs, so they are available in the component the logs are being forwarded to. There are at least two options:

Option 1

Add a boolean option to loki.source.podlogs to keep and forward all discovered labels.

Option 2

Add a block for relabing rules to loki.source.podlogs. The relabeling rules the could be merged with the rules from the PodLogs CR or could be applied beforehand.

[QuentinBisson]

The code is here

alloy/internal/component/loki/source/podlogs/reconciler.go

Line 264 in d899658

discoveredPod.Containers = append(discoveredPod.Containers, DiscoveredContainer{

I would be able to contribute a solution but I need to know what the maintainers would like to do here :)