HTTPRoute Request Mirroring
4 minute read
The HTTPRoute resource allows one or more backendRefs to be provided. Requests will be routed to these upstreams. It is possible to divide the traffic between these backends using Traffic Splitting, but it is also possible to mirror requests to another Service instead. Request mirroring is accomplished using Gateway API’s HTTPRequestMirrorFilter on the HTTPRoute.
When requests are made to a HTTPRoute that uses a HTTPRequestMirrorFilter, the response will never come from the backendRef defined in the filter. Responses from the mirror backendRef are always ignored.
Installation
Follow the steps from the Quickstart to install Envoy Gateway and the example manifest. Before proceeding, you should be able to query the example backend using HTTP.
Mirroring the Traffic
Next, create a new Deployment and Service to mirror requests to. The following example will use
a second instance of the application deployed in the quickstart.
kubectl apply -f - <<EOF
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: backend-2
---
apiVersion: v1
kind: Service
metadata:
name: backend-2
labels:
app: backend-2
service: backend-2
spec:
ports:
- name: http
port: 3000
targetPort: 3000
selector:
app: backend-2
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: backend-2
spec:
replicas: 1
selector:
matchLabels:
app: backend-2
version: v1
template:
metadata:
labels:
app: backend-2
version: v1
spec:
serviceAccountName: backend-2
containers:
- image: gcr.io/k8s-staging-gateway-api/echo-basic:v20231214-v1.0.0-140-gf544a46e
imagePullPolicy: IfNotPresent
name: backend-2
ports:
- containerPort: 3000
env:
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- name: NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
EOF
Then create an HTTPRoute that uses a HTTPRequestMirrorFilter to send requests to the original
service from the quickstart, and mirror request to the service that was just deployed.
kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
name: http-mirror
spec:
parentRefs:
- name: eg
hostnames:
- backends.example
rules:
- matches:
- path:
type: PathPrefix
value: /
filters:
- type: RequestMirror
requestMirror:
backendRef:
kind: Service
name: backend-2
port: 3000
backendRefs:
- group: ""
kind: Service
name: backend
port: 3000
EOF
The HTTPRoute status should indicate that it has been accepted and is bound to the example Gateway.
kubectl get httproute/http-mirror -o yaml
Get the Gateway’s address:
export GATEWAY_HOST=$(kubectl get gateway/eg -o jsonpath='{.status.addresses[0].value}')
Querying backends.example/get should result in a 200 response from the example Gateway and the output from the
example app should indicate which pod handled the request. There is only one pod in the deployment for the example app
from the quickstart, so it will be the same on all subsequent requests.
$ curl -v --header "Host: backends.example" "http://${GATEWAY_HOST}/get"
...
> GET /get HTTP/1.1
> Host: backends.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
<
...
"namespace": "default",
"ingress": "",
"service": "",
"pod": "backend-79665566f5-s589f"
...
Check the logs of the pods and you will see that the original deployment and the new deployment each got a request:
$ kubectl logs deploy/backend && kubectl logs deploy/backend-2
...
Starting server, listening on port 3000 (http)
Echoing back request made to /get to client (10.42.0.10:41566)
Starting server, listening on port 3000 (http)
Echoing back request made to /get to client (10.42.0.10:45096)
Multiple BackendRefs
When an HTTPRoute has multiple backendRefs and an HTTPRequestMirrorFilter, traffic splitting will still behave the same as it normally would for the main backendRefs while the backendRef of the HTTPRequestMirrorFilter will continue receiving mirrored copies of the incoming requests.
cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
name: http-mirror
spec:
parentRefs:
- name: eg
hostnames:
- backends.example
rules:
- matches:
- path:
type: PathPrefix
value: /
filters:
- type: RequestMirror
requestMirror:
backendRef:
kind: Service
name: backend-2
port: 3000
backendRefs:
- group: ""
kind: Service
name: backend
port: 3000
- group: ""
kind: Service
name: backend-3
port: 3000
EOF
Multiple HTTPRequestMirrorFilters
Multiple HTTPRequestMirrorFilters are not supported on the same HTTPRoute rule. When attempting to do so, the admission webhook will reject the configuration.
cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
name: http-mirror
spec:
parentRefs:
- name: eg
hostnames:
- backends.example
rules:
- matches:
- path:
type: PathPrefix
value: /
filters:
- type: RequestMirror
requestMirror:
backendRef:
kind: Service
name: backend-2
port: 3000
- type: RequestMirror
requestMirror:
backendRef:
kind: Service
name: backend-3
port: 3000
backendRefs:
- group: ""
kind: Service
name: backend
port: 3000
EOF
Error from server: error when creating "STDIN": admission webhook "validate.gateway.networking.k8s.io" denied the request: spec.rules[0].filters: Invalid value: "RequestMirror": cannot be used multiple times in the same rule
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