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Documentation Grafana Alloy Reference Components prometheus prometheus.relabel

prometheus.relabel

Prometheus metrics follow the OpenMetrics format. Each time series is uniquely identified by its metric name, plus optional key-value pairs called labels. Each sample represents a datapoint in the time series and contains a value and an optional timestamp.

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<metric name>{<label_1>=<label_val_1>, <label_2>=<label_val_2> ...} <value> [timestamp]

The prometheus.relabel component rewrites the label set of each metric passed along to the exported receiver by applying one or more relabeling rules. If no rules are defined or applicable to some metrics, then those metrics are forwarded as-is to each receiver passed in the component’s arguments. If no labels remain after the relabeling rules are applied, then the metric is dropped.

The most common use of prometheus.relabel is to filter Prometheus metrics or standardize the label set that’s passed to one or more downstream receivers. The rule blocks are applied to the label set of each metric in order of their appearance in the configuration file. The configured rules can be retrieved by calling the function in the rules export field.

You can specify multiple prometheus.relabel components by giving them different labels.

Usage

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prometheus.relabel "<LABEL>" {
  forward_to = <RECEIVER_LIST>

  rule {
    ...
  }

  ...
}

Arguments

You can use the following arguments with prometheus.relabel:

Blocks

You can use the following block with prometheus.relabel:

rule

Exported fields

The following fields are exported and can be referenced by other components:

Component health

prometheus.relabel is only reported as unhealthy if given an invalid configuration. In those cases, exported fields are kept at their last healthy values.

Debug information

prometheus.relabel doesn’t expose any component-specific debug information.

Debug metrics

• prometheus_fanout_latency (histogram): Write latency for sending to direct and indirect components.
• prometheus_forwarded_samples_total (counter): Total number of samples sent to downstream components.
• prometheus_relabel_cache_hits (counter): Total number of cache hits.
• prometheus_relabel_cache_misses (counter): Total number of cache misses.
• prometheus_relabel_cache_size (gauge): Total size of relabel cache.
• prometheus_relabel_metrics_processed (counter): Total number of metrics processed.
• prometheus_relabel_metrics_written (counter): Total number of metrics written.

Example

The following example shows how the prometheus.relabel component applies relabel rules to the incoming metrics, and forwards the results to prometheus.remote_write.onprem.receiver:

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prometheus.relabel "keep_backend_only" {
  forward_to = [prometheus.remote_write.onprem.receiver]

  rule {
    action        = "replace"
    source_labels = ["__address__", "instance"]
    separator     = "/"
    target_label  = "host"
  }
  rule {
    action        = "keep"
    source_labels = ["app"]
    regex         = "backend"
  }
  rule {
    action = "labeldrop"
    regex  = "instance"
  }
}

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metric_a{__address__ = "localhost", instance = "development", app = "frontend"} 10
metric_a{__address__ = "localhost", instance = "development", app = "backend"}  2
metric_a{__address__ = "cluster_a", instance = "production",  app = "frontend"} 7
metric_a{__address__ = "cluster_a", instance = "production",  app = "backend"}  9
metric_a{__address__ = "cluster_b", instance = "production",  app = "database"} 4

After applying the first rule, the replace action populates a new label named host by concatenating the contents of the __address__ and instance labels, separated by a slash /.

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metric_a{host = "localhost/development", __address__ = "localhost", instance = "development", app = "frontend"} 10
metric_a{host = "localhost/development", __address__ = "localhost", instance = "development", app = "backend"}  2
metric_a{host = "cluster_a/production",  __address__ = "cluster_a", instance = "production",  app = "frontend"} 7
metric_a{host = "cluster_a/production",  __address__ = "cluster_a", instance = "production",  app = "backend"}  9
metric_a{host = "cluster_b/production",  __address__ = "cluster_a", instance = "production",  app = "database"} 4

On the second relabeling rule, the keep action only keeps the metrics whose app label matches regex, dropping everything else, so the list of metrics is trimmed down to:

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metric_a{host = "localhost/development", __address__ = "localhost", instance = "development", app = "backend"}  2
metric_a{host = "cluster_a/production",  __address__ = "cluster_a", instance = "production",  app = "backend"}  9

The third and final relabeling rule which uses the labeldrop action removes the instance label from the set of labels.

So in this case, the initial set of metrics passed to the exported receiver is:

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metric_a{host = "localhost/development", __address__ = "localhost", app = "backend"}  2
metric_a{host = "cluster_a/production",  __address__ = "cluster_a", app = "backend"}  9

The two resulting metrics are then propagated to each receiver defined in the forward_to argument.

Compatible components

prometheus.relabel can accept arguments from the following components:

• Components that export Prometheus MetricsReceiver

prometheus.relabel has exports that can be consumed by the following components:

• Components that consume Prometheus MetricsReceiver