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Grafana Loki documentation Send data Promtail Pipeline stages structured_metadata

structured_metadata

The structured_metadata stage is an action stage that takes data from the extracted map and modifies the structured metadata that is sent to Loki with the log entry.

Schema

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structured_metadata:
  # Key is REQUIRED and the name for the label of structured metadata that will be created.
  # Value is optional and will be the name from extracted data whose value
  # will be used for the value of the label. If empty, the value will be
  # inferred to be the same as the key.
  [ <string>: [<string>] ... ]

Examples

Parse from log entry

For the given pipeline:

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- json:
    expressions:
      stream: stream
      traceID: traceID
- labels:
    stream:
- structured_metadata:
    traceID:

Given the following log line:

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{"log":"log message\n","stream":"stderr","traceID":"0242ac120002",time":"2019-04-30T02:12:41.8443515Z"}

The first stage would extract stream with a value of stderr and traceID with a value of 0242ac120002 into the extracted data set. The labels stage would turn that stream and stderr key-value pair into a stream label. The structured_metadata stage would attach the traceID and 0242ac120002 key-value pair as a structured metadata to the log line.

Parse from service discovery labels

For the configuration below, you can use labels from relabel_configs to use as structured_metadata:

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pipeline_stages:
  - structured_metadata:
      pod_uid:
      pod_host_ip:
relabel_configs:
  - action: replace
    source_labels:
      - __meta_kubernetes_pod_uid
    target_label: pod_uid
  - action: replace
    source_labels:
      - __meta_kubernetes_pod_host_ip
    target_label: pod_host_ip

Given the following discovered labels below with a log line sample log:

The structured_metadata stage would turn the discovered labels pod_uid and pod_host_ip into key-value pairs as structured metadata for the log line sample log and exclude them from creating high-cardinality streams.