.. _config_thrift_filters_header_to_metadata: Envoy Header-To-Metadata Filter =============================== * :ref:`v3 API reference ` * This filter should be configured with the name *envoy.filters.http.header_to_metadata*. This filter is configured with rules that will be matched against requests. Each rule has either a header and can be triggered either when the header is present or missing. When a rule is triggered, dynamic metadata will be added based on the configuration of the rule. If the header is present, it's value is extracted and used along with the specified key as metadata. If the header is missing, on missing case is triggered and the value specified is used for adding metadata. The metadata can then be used for load balancing decisions, consumed from logs, etc. A typical use case for this filter is to dynamically match requests with load balancer subsets. For this, a given header's value would be extracted and attached to the request as dynamic metadata which would then be used to match a subset of endpoints. Example ------- A sample filter configuration to route traffic to endpoints based on the presence or absence of a version header could be: .. code-block:: yaml thrift_filters: - name: envoy.filters.thrift.header_to_metadata typed_config: "@type": type.googleapis.com/envoy.extensions.filters.thrift.header_to_metadata.v3.HeaderToMetadata request_rules: - header: x-version on_header_present: metadata_namespace: envoy.lb key: version type: STRING on_header_missing: metadata_namespace: envoy.lb key: default value: 'true' type: STRING remove: false A corresponding upstream cluster configuration could be: .. code-block:: yaml clusters: - name: versioned-cluster type: EDS lb_policy: ROUND_ROBIN lb_subset_config: fallback_policy: ANY_ENDPOINT subset_selectors: - keys: - default - keys: - version This would then allow requests with the ``x-version`` header set to be matched against endpoints with the corresponding version. Whereas requests with that header missing would be matched with the default endpoints. If the header's value needs to be transformed before it's added to the request as dynamic metadata, this filter supports regex matching and substitution: .. code-block:: yaml thrift_filters: - name: envoy.filters.thrift.header_to_metadata typed_config: "@type": type.googleapis.com/envoy.extensions.filters.thrift.header_to_metadata.v3.HeaderToMetadata request_rules: - header: ":path" on_header_present: metadata_namespace: envoy.lb key: cluster regex_value_rewrite: pattern: google_re2: {} regex: "^/(cluster[\\d\\w-]+)/?.*$" substitution: "\\1" Statistics ---------- Currently, this filter generates no statistics.