Add docs on the configuration variables for gateway API (#236)

Author: liwenwu-amazon

docs/enviroment.md

@@ -0,0 +1,129 @@
+### Configuration Variables
+AWS Gateway API Controller for VPC Lattice supports a number of configuration options, which are set through environment variables.
+The following environment variables are available, and all of them are optional.
+
+---
+
+#### `CLUSTER_VPC_ID`
+
+Type: string
+
+Default: ""
+
+When running AWS Gateway API Controller outside the Kubernetes Cluster, this specify the VPC of the cluster.
+
+---
+
+#### `AWS_ACCOUNT_ID`
+
+Type: string
+
+Default: ""
+
+When running AWS Gateway API Controller outside the Kubernetes Cluster, this specify the AWS account.
+
+---
+
+#### `REGION`
+
+Type: string
+
+Default: "us-west-2"
+
+When running AWS Gateway API Controller outside the Kubernetes Cluster, this specify the region of VPC lattice service endpoint
+
+---
+
+#### `GATEWAY_API_CONTROLLER_LOGLEVEL`
+
+Type: string
+
+Default: "info"
+
+When it is set as "debug", the AWS Gateway API Controller prints detailed debugging information.  Otherwise, it is only prints the key information
+
+
+---
+
+#### `CLUSTER_LOCAL_GATEWAY`
+
+Type: string
+
+Default: "NO_DEFAULT_SERVICE_NETWORK"
+
+When it is set to something different than "NO_DEFAULT_SERVICE_NETWORK", the AWS Gateway API Controller will associate its correspoding Lattice Service Network to cluster's VPC.  Also, all HTTPRoutes will automatically have an additional parentref to this `CLUSTER_LOCAL_GATEWAY`
+
+---
+
+#### `TARGET_GROUP_NAME_LEN_MODE`
+
+Type: string
+
+Default:  "short"
+
+***If it is set to "long"*** 
+ AWS Gateway API will create Lattice Target Group as follows
+
+for backendRef of a Kubernetes Service:
+
+k8s-(k8s service name)-(k8s service namespace)-(k8s httproute name)-(VPC ID)
+
+for serviceexport of a Kubernetes Servic:
+
+k8s-(k8s service name)-(k8s service namespace)-(VPC-ID)
+
+***By default***
+  AWS Gateway API will create Lattice Target Group as follows
+
+for backendRef of a Kubernetes Service:
+
+k8s-(k8s service name)-(k8s service namespace)
+
+for serviceexport of a Kubernetes Service:
+
+k8s-(k8s service name)-(k8s service namespace)
+
+
+```
+# for  examples/inventory-route.yaml 
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: inventory
+spec:
+  parentRefs:
+  - name: my-hotel
+    sectionName: http
+  rules:
+  - backendRefs:
+    - name: inventory-ver1
+      kind: Service
+      port: 8090
+      weight: 10
+
+ # by default, lattice target group name 
+ k8s-inventory-ver1-default
+
+
+ # when TARGET_GROUP_NAME_LEN_MODE = "long", lattice target group name, e.g.
+
+ k8s-inventory-ver1-default-inventory-vpc-05c7322a3df3f255a
+
+```
+
+```
+# for examples/parking-ver2-export.yaml 
+apiVersion: multicluster.x-k8s.io/v1alpha1
+kind: ServiceExport
+metadata:
+  name: parking-ver2
+  annotations:
+    multicluster.x-k8s.io/federation: "amazon-vpc-lattice"
+
+# by default, lattice target group name is
+k8s-parking-ver2-default
+
+# when TARGET_GROUP_NAME_LEN_MODE = "long", lattice target group name, e.g.
+k8s-parking-ver2-default-vpc-05c7322a3df3f255a
+
+```