Envoy Header-To-Metadata Filter

  • This filter should be configured with the type URL type.googleapis.com/envoy.extensions.filters.http.header_to_metadata.v3.Config.

  • v3 API reference

This filter is configured with rules that will be matched against requests and responses. Each rule has either a cookie or a header and can be triggered either when the header or cookie is present or missing.

When a rule is triggered, dynamic metadata will be added based on the configuration of the rule. If the header or cookie is present, it’s value is extracted and used along with the specified key as metadata. If the header or cookie 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:

25          http_filters:
26          - name: envoy.filters.http.header_to_metadata
27            typed_config:
28              "@type": type.googleapis.com/envoy.extensions.filters.http.header_to_metadata.v3.Config
29              request_rules:
30              - header: x-version
31                on_header_present:
32                  metadata_namespace: envoy.lb
33                  key: version
34                  type: STRING
35                on_header_missing:
36                  metadata_namespace: envoy.lb
37                  key: default
38                  value: "true"
39                  type: STRING
40                remove: false

As with headers, the value of the specified cookie will be extracted from the request and added as metadata with the key specified. Removing a cookie when a rule matches is unsupported.

25          http_filters:
26          - name: envoy.filters.http.header_to_metadata
27            typed_config:
28              "@type": type.googleapis.com/envoy.extensions.filters.http.header_to_metadata.v3.Config
29              request_rules:
30              - cookie: cookie
31                on_header_present:
32                  metadata_namespace: envoy.lb
33                  key: version
34                  type: STRING
35                on_header_missing:
36                  metadata_namespace: envoy.lb
37                  key: default
38                  value: 'true'
39                  type: STRING
40                remove: false

A corresponding upstream cluster configuration could be:

45  clusters:
46  - name: versioned-cluster
47    type: STRICT_DNS
48    lb_policy: ROUND_ROBIN
49    lb_subset_config:
50      fallback_policy: ANY_ENDPOINT
51      subset_selectors:
52        - keys:
53            - default
54        - keys:
55            - 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:

25          http_filters:
26          - name: envoy.filters.http.header_to_metadata
27            typed_config:
28              "@type": type.googleapis.com/envoy.extensions.filters.http.header_to_metadata.v3.Config
29              request_rules:
30              - header: ":path"
31                on_header_present:
32                  metadata_namespace: envoy.lb
33                  key: cluster
34                  regex_value_rewrite:
35                    pattern:
36                      regex: "^/(cluster[\\d\\w-]+)/?.*$"
37                    substitution: "\\1"

Note that this filter also supports per route configuration:

14          route_config:
15            name: local_route
16            virtual_hosts:
17            - name: local_service
18              domains:
19              - "*"
20              routes:
21              - match:
22                  prefix: "/version-to-metadata"
23                route:
24                  cluster: service
25                typed_per_filter_config:
26                  envoy.filters.http.header_to_metadata:
27                    "@type": type.googleapis.com/envoy.extensions.filters.http.header_to_metadata.v3.Config
28                    request_rules:
29                    - header: x-version
30                      on_header_present:
31                        metadata_namespace: envoy.lb
32                        key: version
33                        type: STRING
34                      remove: false
35              - match:
36                  prefix: "/"
37                route:
38                  cluster: some_service

This can be used to either override the global configuration or if the global configuration is empty (no rules), it can be used to only enable the filter at a per route level.

Statistics

Currently, this filter generates no statistics.