discovery.relabel.md

---

title: discovery.relabel

---

discovery.relabel

In Flow, targets are defined as sets of key-value pairs called labels.

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.

The most common use of discovery.relabel is to filter targets or standardize the target label set that is passed to a downstream component. The rule blocks are applied to the label set of each target in order of their appearance in the configuration file. The configured rules can be retrieved by calling the function in the rules export field.

Target labels which start with a double underscore __ are considered internal, and may be removed by other Flow components prior to telemetry collection. To retain any of these labels, use a labelmap action to remove the prefix, or remap them to a different name. Service discovery mechanisms usually group their labels under __meta_*. For example, the discovery.kubernetes component populates a set of __meta_kubernetes_* labels to provide information about the discovered Kubernetes resources. If a relabeling rule needs to store a label value temporarily, for example as the input to a subsequent step, use the __tmp label name prefix, as it is guaranteed to never be used.

Multiple discovery.relabel components can be specified by giving them different labels.

Usage

discovery.relabel "LABEL" {
  targets = TARGET_LIST

  rule {
    ...
  }

  ...
}

Arguments

The following arguments are supported:

Name	Type	Description	Default	Required
targets	list(map(string))	Targets to relabel		yes

Blocks

The following blocks are supported inside the definition of discovery.relabel:

Hierarchy	Block	Description	Required
rule	rule	Relabeling rules to apply to targets.	no

rule block

{{< docs/shared lookup="flow/reference/components/rule-block.md" source="agent" >}}

Exported fields

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

Name	Type	Description
output	list(map(string))	The set of targets after applying relabeling.
rules	RelabelRules	The currently configured relabeling rules.

Component health

discovery.relabel is only reported as unhealthy when given an invalid configuration. In those cases, exported fields retain their last healthy values.

Debug information

discovery.relabel does not expose any component-specific debug information.

Debug metrics

discovery.relabel does not expose any component-specific debug metrics.

Example

discovery.relabel "keep_backend_only" {
  targets = [
    { "__meta_foo" = "foo", "__address__" = "localhost", "instance" = "one",   "app" = "backend"  },
    { "__meta_bar" = "bar", "__address__" = "localhost", "instance" = "two",   "app" = "database" },
    { "__meta_baz" = "baz", "__address__" = "localhost", "instance" = "three", "app" = "frontend" },
  ]

  rule {
    source_labels = ["__address__", "instance"]
    separator     = "/"
    target_label  = "destination"
    action        = "replace"
  }

  rule {
    source_labels = ["app"]
    action        = "keep"
    regex         = "backend"
  }
}