I am trying to port the follwoing Alloy config to the Otel Collector Distro:

discovery.relabel "metrics_integrations_integrations_test" {
  targets = [{
    __address__ = "localhost:5572",
  }]

  rule {
    target_label = "instance"
    replacement  = constants.hostname
  }
}

prometheus.scrape "metrics_integrations_integrations_test" {
  targets    = discovery.relabel.metrics_integrations_integrations_test.output
  forward_to = [prometheus.remote_write.metrics_service.receiver]
  job_name   = "integrations/test"
}

What I have so far:

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: integrations/test
          scrape_interval: 5s
          static_configs:
        - targets: [localhost:5572]
          basic_auth:
            username: ' '
            password: ' '

processors:
  cumulativetodelta:

exporters:
  otlphttp:
    endpoint: ' '
    headers:
      Authorization: ' '

service:
  pipelines:
    metrics:
      receivers: [prometheus]
      processors: [cumulativetodelta]
      exporters: [otlphttp]

What I do not fully understand is how to convert the discovery.relabel rule to the Collector.

I already tried adding

relabel_configs:
  - source_labels: [__address__]
    target_label: instance

as well as

metric_relabel_configs:
   - source_labels: [__address__]
     target_label: instance

to the scrape configs, but this does not have any effect on the output. So I assume that I don’t understand what discovery.relabel does exactly in that rule. What I think it does is adding a key value pair instance= to every metric as a label. But with the Otel collector I don’t see the label in the output using metric_relabel_configs and relabel_configs.

Can anybody help?