HTTP Request Headers

The HTTPRoute resource can modify the headers of a request before forwarding it to the upstream service. HTTPRoute rules cannot use both filter types at once. Currently, Envoy Gateway only supports core HTTPRoute filters which consist of RequestRedirect and RequestHeaderModifier at the time of this writing. To learn more about HTTP routing, refer to the Gateway API documentation.

A RequestHeaderModifier filter instructs Gateways to modify the headers in requests that match the rule before forwarding the request upstream. Note that the RequestHeaderModifier filter will only modify headers before the request is sent from Envoy to the upstream service and will not affect response headers returned to the downstream client.

Prerequisites

Follow the steps below to install Envoy Gateway and the example manifest. Before proceeding, you should be able to query the example backend using HTTP.

Adding Request Headers

The RequestHeaderModifier filter can add new headers to a request before it is sent to the upstream. If the request does not have the header configured by the filter, then that header will be added to the request. If the request already has the header configured by the filter, then the value of the header in the filter will be appended to the value of the header in the request.

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
        - name: "add-header"
          value: "foo"
EOF

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
        - name: "add-header"
          value: "foo"

The HTTPRoute status should indicate that it has been accepted and is bound to the example Gateway.

kubectl get httproute/http-headers -o yaml

Get the Gateway’s address:

export GATEWAY_HOST=$(kubectl get gateway/eg -o jsonpath='{.status.addresses[0].value}')

Querying headers.example/get should result in a 200 response from the example Gateway and the output from the example app should indicate that the upstream example app received the header add-header with the value: something,foo

$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}/get" --header "add-header: something"
...
> GET /get HTTP/1.1
> Host: headers.example
> User-Agent: curl/7.81.0
> Accept: */*
> add-header: something
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< content-type: application/json
< x-content-type-options: nosniff
< content-length: 474
< x-envoy-upstream-service-time: 0
< server: envoy
<
...
 "headers": {
  "Accept": [
   "*/*"
  ],
  "Add-Header": [
   "something",
   "foo"
  ],
...

Setting Request Headers

Setting headers is similar to adding headers. If the request does not have the header configured by the filter, then it will be added, but unlike adding request headers which will append the value of the header if the request already contains it, setting a header will cause the value to be replaced by the value configured in the filter.

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    matches:
    - path:
        type: PathPrefix
        value: /
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        set:
        - name: "set-header"
          value: "foo"
EOF

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    matches:
    - path:
        type: PathPrefix
        value: /
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        set:
        - name: "set-header"
          value: "foo"

Querying headers.example/get should result in a 200 response from the example Gateway and the output from the example app should indicate that the upstream example app received the header add-header with the original value something replaced by foo.

$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}/get" --header "set-header: something"
...
> GET /get HTTP/1.1
> Host: headers.example
> User-Agent: curl/7.81.0
> Accept: */*
> add-header: something
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< content-type: application/json
< x-content-type-options: nosniff
< content-length: 474
< x-envoy-upstream-service-time: 0
< server: envoy
<
 "headers": {
  "Accept": [
   "*/*"
  ],
  "Set-Header": [
   "foo"
  ],
...

Removing Request Headers

Headers can be removed from a request by simply supplying a list of header names.

Setting headers is similar to adding headers. If the request does not have the header configured by the filter, then it will be added, but unlike adding request headers which will append the value of the header if the request already contains it, setting a header will cause the value to be replaced by the value configured in the filter.

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        remove:
        - "remove-header"
EOF

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        remove:
        - "remove-header"

Querying headers.example/get should result in a 200 response from the example Gateway and the output from the example app should indicate that the upstream example app received the header add-header, but the header remove-header that was sent by curl was removed before the upstream received the request.

$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}/get" --header "add-header: something" --header "remove-header: foo"
...
> GET /get HTTP/1.1
> Host: headers.example
> User-Agent: curl/7.81.0
> Accept: */*
> add-header: something
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< content-type: application/json
< x-content-type-options: nosniff
< content-length: 474
< x-envoy-upstream-service-time: 0
< server: envoy
<

 "headers": {
  "Accept": [
   "*/*"
  ],
  "Add-Header": [
   "something"
  ],
...

Combining Filters

Headers can be added/set/removed in a single filter on the same HTTPRoute and they will all perform as expected

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
        - name: "add-header-1"
          value: "foo"
        set:
        - name: "set-header-1"
          value: "bar"
        remove:
        - "removed-header"
EOF

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
        - name: "add-header-1"
          value: "foo"
        set:
        - name: "set-header-1"
          value: "bar"
        remove:
        - "removed-header"

Early Header Modification

In some cases, it could be necessary to modify headers before the proxy performs any sort of processing, routing or tracing. Envoy Gateway supports this functionality using the ClientTrafficPolicy API.

A ClientTrafficPolicy resource can be attached to a Gateway resource to configure early header modifications for all its routes. In the following example we will demonstrate how early header modification can be configured.

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
  - name: eg
  hostnames:
  - headers.example
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - group: ""
      kind: Service
      name: backend
      port: 3000
      weight: 1
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
          - name: early-added-header
            value: late
          - name: early-set-header
            value: late
          - name: early-removed-header
            value: late 
---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: ClientTrafficPolicy
metadata:
  name: enable-early-headers
  namespace: default
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: Gateway
    name: eg
  headers:
    earlyRequestHeaders:
      add:
        - name: "early-added-header"
          value: "early"
      set:
        - name: "early-set-header"
          value: "early"
      remove:
        - "early-removed-header"
EOF

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-headers
spec:
  parentRefs:
    - name: eg
  hostnames:
    - headers.example
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - group: ""
          kind: Service
          name: backend
          port: 3000
          weight: 1
      filters:
        - type: RequestHeaderModifier
          requestHeaderModifier:
            add:
              - name: early-added-header
                value: late
              - name: early-set-header
                value: late
              - name: early-removed-header
                value: late
---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: ClientTrafficPolicy
metadata:
  name: enable-early-headers
  namespace: default
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: Gateway
    name: eg
  headers:
    earlyRequestHeaders:
      add:
        - name: "early-added-header"
          value: "early"
      set:
        - name: "early-set-header"
          value: "early"
      remove:
        - "early-removed-header"

Querying headers.example/get should result in a 200 response from the example Gateway and the output from the example app should indicate that the upstream example app received the following headers:

• early-added-header contains early (ClientTrafficPolicy) and late (RouteFilter) values
• early-set-header contains only early (ClientTrafficPolicy) and late (RouteFilter) values, since the early modification overwritten the client value.
• early-removed-header contains only the late (RouteFilter) value, since the early modification deleted the client value.

$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}/get" --header  "early-added-header: client" --header  "early-set-header: client" --header  "early-removed-header: client" 
...
> GET /get HTTP/1.1
> Host: headers.example
> User-Agent: curl/7.81.0
> Accept: */*
> add-header: something
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< content-type: application/json
< x-content-type-options: nosniff
< content-length: 474
< x-envoy-upstream-service-time: 0
< server: envoy
<

 "headers": {
  "Accept": [
   "*/*"
  ],
  "Early-Added-Header": [
   "client",
   "early",
   "late"
  ],
  "Early-Set-Header": [
   "early",
   "late"
  ],
  "Early-removed-Header": [
    "late"
  ]
...