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# Description

This example deploys the same infrastructure as the [previous example](../../01-Getting_Started/01-hello_world_1_service_1_deployment), and restricts the access to the gateway based on the domain host from the destination URL.

The domain host targeted will be `my.domain`.

This example configures:

    Generic Kubernetes resources:
    - 1 Service
    - 1 Deployment
    
    Istio resources:
    - 1 Gateway
    - 1 Virtual Service

> **Note:**\
> I don't intend to explain thing related to Kubernetes unless necessary.


# Based on

- [01-hello_world_1_service_1_deployment](../../01-Getting_Started/01-hello_world_1_service_1_deployment)

# Configuration

## Service

Creates a service named `helloworld`.

This service listens for the port `80` expecting `HTTP` traffic and will forward the incoming traffic towards the port `80` from the destination pod.

```yaml
apiVersion: v1
kind: Service
metadata:
  name: helloworld
  labels:
    app: helloworld
    service: helloworld
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: helloworld
```

## Deployment

Deploys a Nginx server that listens for the port `80`.

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: helloworld-nginx
  labels:
    app: helloworld
spec:
  replicas: 1
  selector:
    matchLabels:
      app: helloworld
  template:
    metadata:
      labels:
        app: helloworld
    spec:
      containers:
        - name: helloworld
          image: nginx
          resources:
            requests:
              cpu: "100m"
          imagePullPolicy: IfNotPresent #Always
          ports:
            - containerPort: 80
```

## Gateway

Deploys an Istio gateway that's listening to the port `80` for `HTTP` traffic.

The gateway only will allow the traffic that uses as a URL host: `my.domain`.

The `selector` field is used to "choose" which Istio Load Balancers will have this gateway assigned to.

The Istio `default` profile creates a Load Balancer in the namespace `istio-system` that has the label `istio: ingressgateway` set, allowing us to target that specific Load Balancer and assign this gateway resource to it.

```yaml
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: helloworld-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
    - port:
        number: 80
        name: http
        protocol: HTTP
      hosts:
        - "my.domain"
```

## VirtualService

The Virtual Service resources are used to route and filter the received traffic from the gateway resources, and route it towards the desired destination.

On this example we select the gateway `helloworld-gateway`, which is the [gateway that 's described in the `Gateway` section](#gateway).

On this resource, we are also not limiting the incoming traffic to any specific host, allowing for all the incoming traffic to go through the rules set.

Here we created a rule that will be applied on `HTTP` related traffic (including `HTTPS` and `HTTP2`) when the destination path is exactly `/helloworld`.

This traffic will be forwarded to the port `80` of the destination service `helloworld` (the full path URL equivalent would be `helloworld.$NAMESPACE.svc.cluster.local`).

Additionally, there will be an internal URL rewrite set, as if the URL is not modified, it would attempt to reach to the `/helloworld` path from the Nginx deployment, which currently has no content and would result in an error code `404` (Not found).

```yaml
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: helloworld-vs
spec:
  hosts:
    - "*"
  gateways:
    - helloworld-gateway
  http:
    - match:
        - uri:
            exact: /helloworld
      route:
        - destination:
            host: helloworld
            port:
              number: 80
      rewrite:
        uri: "/"
```

# Walkthrough

## Deploy resources

Deploy the resources.

```shell
kubectl apply -f ./ 
```
```text
deployment.apps/helloworld-nginx created
gateway.networking.istio.io/helloworld-gateway created
service/helloworld created
virtualservice.networking.istio.io/helloworld-vs created
```

## Wait for the deployment to be ready

Wait for the Nginx deployment to be up and ready.

```shell
kubectl get deployment helloworld-nginx -w 
```
```text
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
helloworld-nginx   1/1     1            1           44s
```

## Test the service

### Get LB IP

To perform the desired tests, we will need to obtain the IP Istio Load Balancer that we selected in the [Gateway section](#gateway).

On my environment, the IP is the `192.168.1.50`.

```shell
kubectl get svc -l istio=ingressgateway -A
```
```text
NAME                   TYPE           CLUSTER-IP     EXTERNAL-IP    PORT(S)                                      AGE
istio-ingressgateway   LoadBalancer   10.97.47.216   192.168.1.50   15021:31316/TCP,80:32012/TCP,443:32486/TCP   39h
```

### Curl /helloworld

When performing a curl towards the destination path, as we are not using the domain host specified in the [gateway resource](#gateway), we are failing to match any rule.

```shell
 curl 192.168.1.50/helloworld -I
```
```text
HTTP/1.1 404 Not Found
date: Wed, 10 May 2023 08:25:26 GMT
server: istio-envoy
transfer-encoding: chunked
```

### Curl my.domain/helloworld

We can "fake" the destination domain by modifying the `Host` header.

After setting that up, and attempting to curl the destination, we receive a positive response from the Nginx backend. 

```shell
curl 192.168.1.50/helloworld -s -HHOST:my.domain | grep "<title>.*</title>"
```
```text
<title>Welcome to nginx!</title>
```


## Cleanup

Finally, a cleanup from the resources deployed.

```shell
kubectl delete -f ./
```
```text
deployment.apps "helloworld-nginx" deleted
gateway.networking.istio.io "helloworld-gateway" deleted
service "helloworld" deleted
virtualservice.networking.istio.io "helloworld-vs" deleted
```

# Links of interest

- https://istio.io/latest/docs/reference/config/networking/gateway/