Fingerprint filter plugin

Generates a stable hash from one or more fields so you can deduplicate events, build reproducible document IDs, or pseudonymise values before indexing.

• Package: logstash-filter-fingerprint
• Coverage source: default/bundled
• Official catalog entry: Yes

Plugin overview

fingerprint is used in the Logstash filter stage. Builds stable hashes or fingerprints from selected fields.

Typical use cases

• Transform fields before indexing to keep schema and naming consistent.
• Prepare high-quality fields for alerts, dashboards, and downstream pipelines.

Input and output behavior

• Flow: reads a configured source field and writes parsed/transformed output into a target or root fields.
• Input field: source (default: "message").
• Output target: target (default: ``"[event][hash]" when ECS is enabled).
• Important options: source, target, method, base64encode.

Options

Required

• method (type: string; default: "SHA1") — Hashing method, for example SHA1, SHA256, MURMUR3, or UUID.

Optional

• base64encode (type: boolean; default: false) — Output the fingerprint as a base64 string rather than hex.
• concatenate_sources (type: boolean; default: false) — Combine the values of all source fields before hashing.
• concatenate_all_fields (type: boolean; default: false) — Concatenate every field on the event (use with care; order sensitive).
• ecs_compatibility (type: string) — Controls ECS field compatibility behaviour (disabled, v1, or v8).
• key (type: password; default: none) — Optional secret used for keyed hashes such as HMAC-SHA256.
• source (type: array; default: "message") — Field or list of fields to fingerprint.
• target (type: string; default: "[event][hash]" when ECS is enabled) — Field to receive the generated fingerprint.

Example configuration

filter {
  fingerprint {
    source               => [ "[user][id]", "[event][action]", "@timestamp" ]
    method               => "SHA256"
    concatenate_sources  => true
    target               => "[event][id]"
    base64encode         => true
  }
}

Common options configuration

All Logstash filter plugins support these shared options:

• add_field (type: hash; default: {}) — Adds fields when the filter succeeds. Supports dynamic field names and values.
• add_tag (type: array; default: []) — Adds one or more tags when the filter succeeds.
• enable_metric (type: boolean; default: true) — Enables or disables metric collection for this plugin instance.
• id (type: string; default: none) — Sets an explicit plugin instance ID for monitoring and troubleshooting.
• periodic_flush (type: boolean; default: false) — Calls the filter flush method at regular intervals.
• remove_field (type: array; default: []) — Removes fields when the filter succeeds. Supports dynamic field names.
• remove_tag (type: array; default: []) — Removes tags when the filter succeeds.

filter {
  fingerprint {
    add_field => { "pipeline_stage" => "parsed" }
    add_tag => ["parsed", "logstash_filter"]
    enable_metric => true
    id => "my_filter_instance"
    periodic_flush => false
    remove_field => ["tmp_field"]
    remove_tag => ["temporary"]
  }
}

Apply in Logit.io

1. Open your stack in Logit.io and navigate to Logstash Pipelines.
2. In the filter { ... } section, add a fingerprint block.
3. Save your pipeline changes, then restart the Logstash pipeline if prompted.
4. Send sample events and verify parsed/enriched fields in OpenSearch Dashboards.

Validation checklist

• Confirm the fingerprint block compiles without syntax errors.
• Verify expected new/updated fields exist in sample documents.
• Verify unexpected fields are not removed unless explicitly configured.
• Confirm tags added on success/failure align with your alerting and routing rules.

Troubleshooting

• If events are unchanged, verify your filter condition (if ...) matches incoming events.
• If the pipeline fails to start, validate braces/quotes and retry with a minimal filter block.
• If throughput drops, reduce expensive operations and test with representative sample volume.

References

• GitHub package: logstash-filter-fingerprint (opens in a new tab)
• Canonical catalog: /log-management/ingestion-pipeline/logstash-filters-reference