Alloy sourcemap integration not resolving minified Angular stacktrace

I’m trying to configure Grafana Alloy to resolve my Angular application’s stack traces using source maps, but the mapping isn’t working as expected. Even though I have the sourcemaps downloaded locally, the Alloy logs still show only minified stack traces.

Here’s my Alloy configuration:

sourcemaps {
  download = true
  download_from_origins = ["http://control-center.dev.svc.cluster.local:8081"]
  location {
    path = "/usr/share/nginx/sourcemaps"
    minified_path_prefix = "/"
  }
}

All the source maps are available in the container under /usr/share/nginx/sourcemaps

However, when an error is logged, Grafana still shows minified stack traces like this:

timestamp="2025-10-20 16:23:51.46 +0000 UTC" kind=exception type=Error value="Test Sentry"
stacktrace="Error: Test Sentry
  at c.ngOnInit (https://cpc-tnag-wbpr7v/cc/199.29d616a1968be30c.js:1:10140)
  at At (https://cpc-tnag-wbpr7v/cc/main.56a2acdf792d4034.js:129:306468)
  at xn (https://cpc-tnag-wbpr7v/cc/main.56a2acdf792d4034.js:129:306631)
  at Vh (https://cpc-tnag-wbpr7v/cc/main.56a2acdf792d4034.js:129:306368)
  ...

I was expecting Alloy to automatically map these minified lines back to the corresponding TypeScript/Angular source lines.

What I’ve verified so far:

• All sourcemap files exist inside /usr/share/nginx/sourcemaps.

• The download_from_origins URL (http://control-center.dev.svc.cluster.local:8081) is accessible and returns the .js.map files.

• The minified_path_prefix is set to /, assuming it matches URLs like https://cpc-tnag-wbpr7v/cc/main.56a2acdf792d4034.js.

Question

Is there something wrong or missing in my sourcemaps configuration? Do I need to adjust minified_path_prefix or path to ensure Alloy correctly matches the minified JS URLs (e.g. https://cpc-tnag-wbpr7v/cc/main.56a2acdf792d4034.js) with the corresponding sourcemap files?

Any help or examples of a working setup would be greatly appreciated.

I have tried running the Alloy code below:

apiVersion: v1
kind: ConfigMap
metadata:
  name: alloy-config
  labels:
    {{- include "cai-observability.labels" . | nindent 4 }}
data:
  config.alloy: |-

    // For development only!
    //livedebugging {
    //  enabled = true
    //}

    faro.receiver "faro" {
        server {
          listen_address = "0.0.0.0"
        }

        sourcemaps {
          download = true
          download_from_origins = ["http://control-center.dev.svc.cluster.local:8081"]
          location {
            path = "/usr/share/nginx/sourcemaps"
            minified_path_prefix = "/"
          }
        }
    
        output {
            logs = [loki.process.client_logs.receiver]
            {{- if eq .Values.tempo.enabled true}}
            traces = [otelcol.exporter.otlp.traces.input]
            {{ end }}
        }
    }

    
    logging {
      level  = "debug"    
      format = "logfmt"   
    }

    loki.write "default" {
      endpoint {
        url = "http://cai-observability-loki-gateway/loki/api/v1/push"
      }
    }

    otelcol.exporter.otlp "traces" {
        client {
            endpoint = "cai-observability-tempo"
            tls {
                insecure             = true
                insecure_skip_verify = true
            }                
        }
    }        

    // discovery.kubernetes allows you to find scrape targets from Kubernetes resources.
    // It watches cluster state and ensures targets are continually synced with what is currently running in your cluster.
    discovery.kubernetes "pod" {
      role = "pod"
      namespaces {
        names = [{{- range $index, $ns := .Values.mes.namespaces }}{{ $ns | quote }}{{ if ne $index (sub (len $.Values.mes.namespaces) 1)}}, {{ end }}{{- end}}]
      }
    }

    // discovery.relabel rewrites the label set of the input targets by applying one or more relabeling rules.
    // If no rules are defined, then the input targets are exported as-is.
    discovery.relabel "pod_logs" {
      targets = discovery.kubernetes.pod.targets

      // Label creation - "namespace" field from "__meta_kubernetes_namespace"
      rule {
        source_labels = ["__meta_kubernetes_namespace"]
        action = "replace"
        target_label = "namespace"
      }

      // Label creation - "pod" field from "__meta_kubernetes_pod_name"
      rule {
        source_labels = ["__meta_kubernetes_pod_name"]
        action = "replace"
        target_label = "pod"
      }

      // Label creation - "container" field from "__meta_kubernetes_pod_container_name"
      rule {
        source_labels = ["__meta_kubernetes_pod_container_name"]
        action = "replace"
        target_label = "container"
      }

      // Label creation -  "app" field from "__meta_kubernetes_pod_label_app_kubernetes_io_name"
      rule {
        source_labels = ["__meta_kubernetes_pod_label_app_kubernetes_io_name"]
        action = "replace"
        target_label = "app"
      }

      // Label creation -  "job" field from "__meta_kubernetes_namespace" and "__meta_kubernetes_pod_container_name"
      // Concatenate values __meta_kubernetes_namespace/__meta_kubernetes_pod_container_name
      rule {
        source_labels = ["__meta_kubernetes_namespace", "__meta_kubernetes_pod_container_name"]
        action = "replace"
        target_label = "job"
        separator = "/"
        replacement = "$1"
      }

      // Label creation - "container" field from "__meta_kubernetes_pod_uid" and "__meta_kubernetes_pod_container_name"
      // Concatenate values __meta_kubernetes_pod_uid/__meta_kubernetes_pod_container_name.log
      rule {
        source_labels = ["__meta_kubernetes_pod_uid", "__meta_kubernetes_pod_container_name"]
        action = "replace"
        target_label = "__path__"
        separator = "/"
        replacement = "/var/log/pods/*$1/*.log"
      }

      // Note: We are not using the mes_service label at the moment.
      // Label creation - "mes-service" field from "__meta_kubernetes_pod_labelpresent_caisoft_com_mes_service"
      //rule {
      //  source_labels = ["__meta_kubernetes_pod_labelpresent_caisoft_com_mes_service"]
      //  action = "replace"
      //  target_label = "mes_service"
      //}
    }

    // loki.source.kubernetes tails logs from Kubernetes containers using the Kubernetes API.
    loki.source.kubernetes "pod_logs" {
      targets    = discovery.relabel.pod_logs.output
      forward_to = [loki.process.pod_logs.receiver]
    }

    loki.process "pod_logs" {

      // Current approach
      // 1.  Make sure all entries have a level.
      // 2.  Don't drop any level=info coming from mes-services.
      // 3.  Drop web server access log entries (Nginx, Gin).
      // 4.  Drop all Novu entries.
      // 5.  Drop all MongoDb info entries.  Can be parsed as JSON. "s: I".
      // This will give us the following benefits:
      // 1.  We still have info entries for our services.  This will help us find context while troubleshooting.
      // 2.  We will have the ability to filter entries using the "Level" label.  Grafana UI doesn't always work as expected.
      // 3.  Services that have a significant amount of chatter will be dropped (novu, Mongo info).

      // Health checks to batch scheduler
      stage.drop {
        expression = "GET /api/app/ping"
      }

      // Health checks to Nginx
      stage.drop {
        expression = "kube-probe/"
      }

      // Health and metrics checks to services using golang's Gin framework
      stage.drop {
        expression = `\[GIN\].+"(?:\/healthz|\/metrics)\S*"`
      }

      // Try to extract the log level from JSON
      stage.json {
        expressions = {
          level = "not_null(\"@l\", level, s)",
        }
      }

      // Default level to "info" if it wasn't found
      // Lower case all levels
      stage.template {
        source = "level"
        template = `{{ "{{" }} default "info" .Value | ToLower {{ "}}" }}`
      }

      stage.labels {
        values = {
          "level" = "",
        }
      }

      // Note: This is currently not used, but leaving it here for reference.
      // This if for dropping informational messages from pods containing the mes_sevice label.
      //stage.match {
      //  selector = "{ mes_service=\"true\" }"
      //  stage.drop {
      //    source = "level"
      //    expression = `(?i)^(?:info|information|debug|trace|i|d[1-5])$`
      //  }
      //}

      // Drop all entries from Novu
      stage.drop {
        source = "app"
        expression = `^novu-\S+$`
      }

      // Drop all info entries from Mongodb where "s: I"
      stage.match {
        selector = "{ app=\"mongodb\" }"
        stage.drop {
          source = "level"
          expression = `^i$`
        }
      }

      // Note: Not using mes_service label at this time.
      //stage.label_drop {
      //  values = [ "mes_service" ]
      //}

      forward_to = [loki.relabel.pod_logs.receiver]
    }

    loki.relabel "pod_logs" {

      // Normalize levels

      // i to info
      rule {
        source_labels = ["level"]
        regex         = "i"
        replacement   = "info"
        action        = "replace"
        target_label  = "level"
      }

      // w or warn to warning
      rule {
        source_labels = ["level"]
        regex         = "(w|warn)"
        replacement   = "warning"
        action        = "replace"
        target_label  = "level"
      }

      // e or f to error
      rule {
        source_labels = ["level"]
        regex         = "(e|f)"
        replacement   = "error"
        action        = "replace"
        target_label  = "level"
      }

      // d to debug
      rule {
        source_labels = ["level"]
        regex         = "d"
        replacement   = "debug"
        action        = "replace"
        target_label  = "level"
      }

      forward_to = [loki.write.default.receiver]
    }

    loki.process "client_logs" {

      stage.logfmt {
          mapping = { "kind" = "", "app_name" = "", "app_namespace" = "" }
      }

      stage.labels {
          values = { "kind" = "kind", "app" = "app_name", "namespace" = "app_namespace", "client" = "app_name" }
      }        
      forward_to = [loki.write.default.receiver]
    }