When we want to use match with headers and some filter add/replace a header, the decorator or tracing doesn’t work correctly.

Test

We use the x-pool header to match the route and we inject this header in a filter.

In this example, we do a lower() of the header, and if the header is not modified, the decorator is correctly added and the request is sampled, but if we send the header with a capital letter, and it is modified, the request is routed correctly, but the decorator is not added and the request is not sampled.

OK:

curl -v localhost:8000/ -H "x-pool:pool"
> GET / HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.77.0
> Accept: */*
> x-pool:pool
> 
< HTTP/1.1 200 OK
< x-sampled: True
< content-type: text/html; charset=utf-8
< content-length: 111
< server: envoy
< date: Fri, 19 Nov 2021 19:51:23 GMT
< x-envoy-upstream-service-time: 23
< x-envoy-decorator-operation: test

No add decorator and tracing:

curl -v localhost:8000/ -H "x-pool:POOL"
> GET / HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.77.0
> Accept: */*
> x-pool:POOL
> 
< HTTP/1.1 200 OK
< x-sampled: False
< content-type: text/html; charset=utf-8
< content-length: 111
< server: envoy
< date: Fri, 19 Nov 2021 19:53:21 GMT
< x-envoy-upstream-service-time: 26

Config

static_resources:
  listeners:
  - address:
      socket_address:
        address: 0.0.0.0
        port_value: 8000
    traffic_direction: INBOUND
    filter_chains:
    - filters:
      - name: envoy.filters.network.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          http_filters:
            - name: envoy.filters.http.lua
              typed_config:
                "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
                inline_code: |
                  function envoy_on_request(request_handle)
                    local originalHeader = request_handle:headers():get("x-pool")
                    if originalHeader then
                      request_handle:headers():remove("x-pool")
                      request_handle:headers():add("x-pool", originalHeader:lower())
                    end
                  end
            - name: envoy.filters.http.router
              typed_config: {}
          request_id_extension:
            typed_config:
              "@type": type.googleapis.com/envoy.extensions.request_id.uuid.v3.UuidRequestIdConfig
              pack_trace_reason: false
          generate_request_id: true
          tracing:
            verbose: true
            client_sampling:
              value: 0.0
            random_sampling:
              value: 0.0
            overall_sampling:
              value: 100.0
            provider:
              name: envoy.tracers.zipkin
              typed_config:
                "@type": type.googleapis.com/envoy.config.trace.v3.ZipkinConfig
                collector_cluster: otel 
                collector_endpoint: "/api/v2/spans"
                shared_span_context: true
                collector_endpoint_version: HTTP_JSON
          codec_type: AUTO
          stat_prefix: ingress_http
          route_config:
            name: reverse_proxy
            virtual_hosts:
            - name: pool
              domains:
              - "*"
              routes:
              - match:
                  prefix: "/"
                  headers:
                  - name: x-pool
                    exact_match: pool
                route:
                  cluster: cluster.test
                decorator:
                  operation: test
                tracing:
                  client_sampling:
                    numerator: 100
                  random_sampling:
                    numerator: 100
                  overall_sampling:
                    numerator: 100
  clusters:
  - name: cluster.test
    type: STRICT_DNS
    lb_policy: ROUND_ROBIN
    load_assignment:
      cluster_name: cluster.test
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: service
                port_value: 8080
  - name: otel
    type: STRICT_DNS
    lb_policy: ROUND_ROBIN
    load_assignment:
      cluster_name: otel
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: otel
                port_value: 9411
admin:
  address:
    socket_address:
      address: 0.0.0.0
      port_value: 8001