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Gateway

A Gateway resource exposes services to the outside world and is used often in production environments. From the docs:

A Gateway describes an instance of traffic handling infrastructure. It defines a network endpoint that can be used for processing traffic, i.e. filtering, balancing, splitting, etc. for backends such as a Service. For example, a Gateway may represent a cloud load balancer or an in-cluster proxy server that is configured to accept HTTP traffic.

In the diagram above, the "client" can be anything. It doesn't live inside k8s. It might just be a web browser or a mobile app. The "Gateway-managed load balancer" can be a bit confusing, we'll talk about it more later. For now, just know that it's a load balancer that lives outside the cluster and routes traffic through the Gateway to a service.

Gateway is the newer alternative to Ingress which you might still come across in production systems.

Assignment

The Gateway API is a spec that has different implementations. We're gonna use the Envoy Gateway, which you can install with this command:

kubectl apply --server-side -f https://github.com/envoyproxy/gateway/releases/download/v1.5.1/install.yaml

Then, create a file that we'll call app-gatewayclass.yaml because we want to create a Gateway for the entire synergychat application, not just a specific service.

apiVersion: gateway.networking.k8s.io/v1
kind: GatewayClass
metadata:
  name: app-gatewayclass
spec:
  controllerName: gateway.envoyproxy.io/gatewayclass-controller

We need this GatewayClass because:

Any Gateway we create has to be associated with a GatewayClass
The controllerName is set to the one created while installing the Envoy Gateway

Next, create the actual Gateway in new file named app-gateway.yaml:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: app-gateway
spec:
  gatewayClassName: app-gatewayclass
  listeners:
    - name: http
      protocol: HTTP
      port: 80

Next, we need to define the routing rules for our Gateway with HTTPRoute resources. Set a rule for the web service, which we could save in a file named web-httproute.yaml:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: web-httproute
spec:
  parentRefs:
    - name: app-gateway
  hostnames:
    - "synchat.internal"
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: web-service
          port: 80

... and another for the API service in api-httproute.yaml:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: api-httproute
spec:
  parentRefs:
    - name: app-gateway
  hostnames:
    - "synchatapi.internal"
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: api-service
          port: 80

This says that any traffic to the synchat.internal domain name should be routed to the web-service and any traffic to synchatapi.internal domain name should be routed to the api-service.

Apply all the resources, then run:

kubectl proxy

Run and submit the CLI tests.