docs: fault injection (#2406)

Signed-off-by: nan zhao <tmsnan94@outlook.com>

site/content/en/latest/user/fault-injection.md

@@ -0,0 +1,254 @@
+---
+title: "Fault Injection"
+---
+
+[Envoy fault injection] can be used to inject delays and abort requests to mimic failure scenarios such as service failures and overloads.
+
+Envoy Gateway supports the following fault scenarios:
+- **delay fault**: inject a custom fixed delay into the request with a certain probability to simulate delay failures.
+- **abort fault**: inject a custom response code into the response with a certain probability to simulate abort failures.
+
+Envoy Gateway introduces a new CRD called [BackendTrafficPolicy][] that allows the user to describe their desired fault scenarios.
+This instantiated resource can be linked to a [Gateway][], [HTTPRoute][] or [GRPCRoute][] resource.
+
+## Prerequisites
+
+Follow the steps from the [Quickstart](../quickstart) guide to install Envoy Gateway and the example manifest.
+For GRPC - follow the steps from the [GRPC Routing](../grpc-routing) example.
+Before proceeding, you should be able to query the example backend using HTTP or GRPC.
+
+### Install the hey load testing tool
+* The `hey` CLI will be used to generate load and measure response times. Follow the installation instruction from the [Hey project] docs.
+
+## Configuration
+
+Allow requests with a valid faultInjection by creating an [BackendTrafficPolicy][BackendTrafficPolicy] and attaching it to the example HTTPRoute or GRPCRoute.
+
+### HTTPRoute
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.envoyproxy.io/v1alpha1
+kind: BackendTrafficPolicy
+metadata:
+  name: fault-injection-50-percent-abort
+spec:
+  targetRef:
+    group: gateway.networking.k8s.io
+    kind: HTTPRoute
+    name: foo
+  faultInjection:
+    abort:
+      httpStatus: 501
+      percentage: 50
+---
+apiVersion: gateway.envoyproxy.io/v1alpha1
+kind: BackendTrafficPolicy
+metadata:
+  name: fault-injection-delay
+spec:
+  targetRef:
+    group: gateway.networking.k8s.io
+    kind: HTTPRoute
+    name: bar
+  faultInjection:
+    delay:
+      fixedDelay: 2s
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: foo
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - "www.example.com"
+  rules:
+  - backendRefs:
+    - group: ""
+      kind: Service
+      name: backend
+      port: 3000
+      weight: 1
+    matches:
+    - path:
+        type: PathPrefix
+        value: /foo
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: bar
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - "www.example.com"
+  rules:
+  - backendRefs:
+    - group: ""
+      kind: Service
+      name: backend
+      port: 3000
+      weight: 1
+    matches:
+    - path:
+        type: PathPrefix
+        value: /bar
+
+EOF
+```
+
+Two HTTPRoute has been created, one for `/foo` and another for `/bar`.  `fault-injection-abort` BackendTrafficPolicy has been created and targeted HTTPRoute foo to abort requests for `/foo`. `fault-injection-delay` BackendTrafficPolicy has been created and targeted HTTPRoute foo to delay `2s` requests for `/bar`. 
+
+Verify the HTTPRoute configuration and status:
+
+```shell
+kubectl get httproute/foo -o yaml
+kubectl get httproute/bar -o yaml
+```
+
+Verify the BackendTrafficPolicy configuration:
+
+```shell
+kubectl get backendtrafficpolicy/fault-injection-50-percent-abort -o yaml
+kubectl get backendtrafficpolicy/fault-injection-delay -o yaml
+```
+
+### GRPCRoute
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.envoyproxy.io/v1alpha1
+kind: BackendTrafficPolicy
+metadata:
+  name: fault-injection-abort
+spec:
+  targetRef:
+    group: gateway.networking.k8s.io
+    kind: GRPCRoute
+    name: yages
+  faultInjection:
+    abort:
+      grpcStatus: 14
+---
+apiVersion: gateway.networking.k8s.io/v1alpha2
+kind: GRPCRoute
+metadata:
+  name: yages
+  labels:
+    example: grpc-routing
+spec:
+  parentRefs:
+  - name: example-gateway
+  hostnames:
+  - "grpc-example.com"
+  rules:
+  - backendRefs:
+    - group: ""
+      kind: Service
+      name: yages
+      port: 9000
+      weight: 1
+EOF
+```
+
+A BackendTrafficPolicy has been created and targeted GRPCRoute yages to abort requests for `yages` service..
+
+Verify the GRPCRoute configuration and status:
+
+```shell
+kubectl get grpcroute/yages -o yaml
+```
+
+Verify the SecurityPolicy configuration:
+
+```shell
+kubectl get backendtrafficpolicy/fault-injection-abort -o yaml
+```
+
+## Testing
+
+Ensure the `GATEWAY_HOST` environment variable from the [Quickstart](../quickstart) guide is set. If not, follow the
+Quickstart instructions to set the variable.
+
+```shell
+echo $GATEWAY_HOST
+```
+
+### HTTPRoute
+
+Verify that requests to `foo` route are aborted.
+
+```shell
+hey -n 1000 -c 100 -host "www.example.com"  http://${GATEWAY_HOST}/foo
+```
+
+```console
+Status code distribution:
+  [200]	501 responses
+  [501]	499 responses
+```
+
+Verify that requests to `bar` route are delayed.
+
+```shell
+hey -n 1000 -c 100 -host "www.example.com"  http://${GATEWAY_HOST}/bar
+```
+
+```console
+Summary:
+  Total:	20.1493 secs
+  Slowest:	2.1020 secs
+  Fastest:	1.9940 secs
+  Average:	2.0123 secs
+  Requests/sec:	49.6295
+
+  Total data:	557000 bytes
+  Size/request:	557 bytes
+
+Response time histogram:
+  1.994 [1]	|
+  2.005 [475]	|■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
+  2.016 [419]	|■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
+  2.026 [5]	|
+  2.037 [0]	|
+  2.048 [0]	|
+  2.059 [30]	|■■■
+  2.070 [0]	|
+  2.080 [0]	|
+  2.091 [11]	|■
+  2.102 [59]	|■■■■■
+```
+
+### GRPCRoute
+
+Verify that requests to `yages`service are aborted.
+
+```shell
+grpcurl -plaintext -authority=grpc-example.com ${GATEWAY_HOST}:80 yages.Echo/Ping
+```
+
+You should see the below response
+
+```shell
+Error invoking method "yages.Echo/Ping": rpc error: code = Unavailable desc = failed to query for service descriptor "yages.Echo": fault filter abort
+```
+
+## Clean-Up
+
+Follow the steps from the [Quickstart](../quickstart) guide to uninstall Envoy Gateway and the example manifest.
+
+Delete the BackendTrafficPolicy:
+
+```shell
+kubectl delete BackendTrafficPolicy/fault-injection-abort
+```
+
+[Envoy fault injection]: https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/fault_filter.html
+[BackendTrafficPolicy]: ../../api/extension_types#backendtrafficpolicy
+[Gateway]: https://gateway-api.sigs.k8s.io/api-types/gateway/
+[HTTPRoute]: https://gateway-api.sigs.k8s.io/api-types/httproute/
+[GRPCRoute]: https://gateway-api.sigs.k8s.io/api-types/grpcroute/
+[Hey project]: https://github.com/rakyll/hey