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Purpose-built Knative Ingress implementation using just Envoy with no additional CRDs

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# Kourier

**[This component is GA](https://github.com/knative/community/tree/main/mechanics/MATURITY-LEVELS.md)**

Kourier is an Ingress for [Knative Serving](https://knative.dev/). Kourier is a
lightweight alternative for the Istio ingress as its deployment consists only of
an Envoy proxy and a control plane for it.

Kourier is passing the knative serving e2e and conformance tests:
[Kourier Testgrid](https://testgrid.knative.dev/serving#kourier-stable).

- [**Getting started**](#getting-started)
- [**Features**](#features)
- [**Deployment**](#deployment)
- [**License**](#license)

## Getting started

- Install Knative Serving, ideally without Istio:

```bash
kubectl apply -f https://github.com/knative/serving/releases/latest/download/serving-crds.yaml
kubectl apply -f https://github.com/knative/serving/releases/latest/download/serving-core.yaml
```

- Then install Kourier:

```bash
kubectl apply -f https://github.com/knative/net-kourier/releases/latest/download/kourier.yaml
```

- Configure Knative Serving to use the proper "ingress.class":

```bash
kubectl patch configmap/config-network \
  -n knative-serving \
  --type merge \
  -p '{"data":{"ingress.class":"kourier.ingress.networking.knative.dev"}}'
```

- (OPTIONAL) Set your desired domain (replace 127.0.0.1.nip.io to your preferred
  domain):

```bash
kubectl patch configmap/config-domain \
  -n knative-serving \
  --type merge \
  -p '{"data":{"127.0.0.1.nip.io":""}}'
```

- (OPTIONAL) Deploy a sample hello world app:

```bash
cat <<-EOF | kubectl apply -f -
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-go
spec:
  template:
    spec:
      containers:
      - image: gcr.io/knative-samples/helloworld-go
        env:
        - name: TARGET
          value: Go Sample v1
EOF
```

- (OPTIONAL) For testing purposes, you can use port-forwarding to make requests
  to Kourier from your machine:

```bash
kubectl port-forward --namespace kourier-system $(kubectl get pod -n kourier-system -l "app=3scale-kourier-gateway" --output=jsonpath="{.items[0].metadata.name}") 8080:8080 19000:9000 8443:8443

curl -v -H "Host: helloworld-go.default.127.0.0.1.nip.io" http://localhost:8080
```

## Deployment

By default, the deployment of the Kourier components is split between two
different namespaces:

- Kourier control is deployed in the `knative-serving` namespace
- The kourier gateways are deployed in the `kourier-system` namespace

To change the Kourier gateway namespace, you will need to:

- Modify the files in `config/` and replace all the namespaces fields that have
  `kourier-system` with the desired namespace.
- Set the `KOURIER_GATEWAY_NAMESPACE` env var in the kourier-control deployment
  to the new namespace.

## Features

- Traffic splitting between Knative revisions.
- Automatic update of endpoints as they are scaled.
- Support for gRPC services.
- Timeouts and retries.
- TLS
- Cipher Suite
- External Authorization support.
- Proxy Protocol (AN EXPERIMENTAL / ALPHA FEATURE)

## Setup TLS certificate

Create a secret containing your TLS certificate and Private key:

```
kubectl create secret tls ${CERT_NAME} --key ${KEY_FILE} --cert ${CERT_FILE}
```

Add the following env vars to net-kourier-controller in the "kourier" container :

```
CERTS_SECRET_NAMESPACE: ${NAMESPACES_WHERE_THE_SECRET_HAS_BEEN_CREATED}
CERTS_SECRET_NAME: ${CERT_NAME}
```

### Cipher Suites

You can specify the cipher suites for TLS external listener.
To specify the cipher suites you want to allow, run the following command to patch `config-kourier` ConfigMap:

```
kubectl -n "knative-serving" patch configmap/config-kourier \
  --type merge \
  -p '{"data":{"cipher-suites":"ECDHE-ECDSA-AES128-GCM-SHA256,ECDHE-ECDSA-CHACHA20-POLY1305"}}'
```

The default uses the default cipher suites of the envoy version.

## External Authorization Configuration

If you want to enable the external authorization support you can set these ENV
vars in the `net-kourier-controller` deployment:

- `KOURIER_EXTAUTHZ_HOST*`: The external authorization service and port,
  my-auth:2222
- `KOURIER_EXTAUTHZ_FAILUREMODEALLOW*`: Allow traffic to go through if the ext
  auth service is down. Accepts true/false
- `KOURIER_EXTAUTHZ_PROTOCOL`: The protocol used to query the ext auth
  service. Can be one of : grpc, http, https. Defaults to grpc
- `KOURIER_EXTAUTHZ_MAXREQUESTBYTES`: Max request bytes, if not set, defaults to
  8192 Bytes. More info
  [Envoy Docs](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/ext_authz/v3/ext_authz.proto.html?highlight=max_request_bytes#extensions-filters-http-ext-authz-v3-buffersettings)
- `KOURIER_EXTAUTHZ_TIMEOUT`: Max time in ms to wait for the ext authz service.
  Defaults to 2s
- `KOURIER_EXTAUTHZ_PATHPREFIX`: If `KOURIER_EXTAUTHZ_PROTOCOL` is equal to
  http or https, path to query the ext auth service. Example : if set to
  `/verify`, it will query `/verify/` (**notice the trailing `/`**).
  If not set, it will query `/`
- `KOURIER_EXTAUTHZ_PACKASBYTES`: If `KOURIER_EXTAUTHZ_PROTOCOL` is equal to
  grpc, sends the body as raw bytes instead of a UTF-8 string. Accepts only true/false, t/f or 1/0.
  Attempting to set another value will throw an error. Defaults to false. More info
  [Envoy Docs](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/ext_authz/v3/ext_authz.proto.html?highlight=pack_as_bytes#extensions-filters-http-ext-authz-v3-buffersettings).

`*` Required

## Distributed Tracing Configuration

Kourier supports distributed tracing via OpenTelemetry Protocol (OTLP). To enable tracing, configure the `config-kourier` ConfigMap:

```bash
kubectl patch configmap/config-kourier \
  -n knative-serving \
  --type merge \
  -p '{"data":{
    "tracing-endpoint":"http://otel-collector.observability.svc:4317",
    "tracing-protocol":"grpc",
    "tracing-sampling-rate":"1.0"
  }}'
```

### Configuration Options

- **`tracing-endpoint`**: The OTLP collector endpoint (e.g., `http://otel-collector.observability.svc:4317` for gRPC or `http://otel-collector.observability.svc:4318` for HTTP)
- **`tracing-protocol`**: The protocol to use for sending traces. Supported values:
  - `grpc`: OTLP over gRPC (default, typically port 4317)
  - `http/protobuf`: OTLP over HTTP with protobuf encoding (typically port 4318)
- **`tracing-sampling-rate`**: Sampling rate for traces, ranging from `0.0` (no sampling) to `1.0` (sample all requests). Default is `1.0`

Kourier propagates W3C trace context headers (`traceparent`, `tracestate`, and `baggage`) to enable distributed tracing across services.

## Proxy Protocol Configuration
Note: this is an experimental/alpha feature.

To enable proxy protocol feature, run the following command to patch `config-kourier` ConfigMap:
```
kubectl patch configmap/config-kourier \
  -n knative-serving \
  --type merge \
  -p '{"data":{"enable-proxy-protocol":"true"}}'
```
Ensure that the file was updated successfully:
```
kubectl get configmap config-kourier --namespace knative-serving --output yaml
```

### LoadBalancer configuration:

We need to:
- Use your LB provider annotation to enable proxy-protocol.
- If you are planning to enable external-domain-tls, use your LB provider annotation to specify a custom name to use for the Load balancer,
  This is used to work around the issue of kube-proxy adding external LB address to node local iptables rule, which will break requests to an LB from in-cluster if the LB is expected to terminate SSL or proxy protocol.
- Change the external Traffic Policy to `local` so the LB we'll preserve the client source IP and avoids a second hop for LoadBalancer.

Example (Scaleway provider):
```
apiVersion: v1
kind: Service
metadata:
  name: kourier
  namespace: kourier-system
  annotations:
    service.beta.kubernetes.io/scw-loadbalancer-proxy-protocol-v2: '*'
    service.beta.kubernetes.io/scw-loadbalancer-use-hostname: "true"
  labels:
    networking.knative.dev/ingress-provider: kourier
spec:
  ports:
    - name: http2
      port: 80
      protocol: TCP
      targetPort: 8080
    - name: https
      port: 443
      protocol: TCP
      targetPort: 8443
  selector:
    app: 3scale-kourier-gateway
  externalTrafficPolicy: Local
  type: LoadBalancer
```

## Tips
Domain Mapping is configured to explicitly use `http2` protocol only. This behaviour can be disabled by adding the following annotation to the Domain Mapping resource
```
kubectl annotate domainmapping <domain_mapping_name> kourier.knative.dev/disable-http2=true --namespace <namespace>
```
A good use case for this configuration is `DomainMapping with Websocket`

Note: This annotation is an experimental/alpha feature. We may change the annotation name in the future.

## License

[Apache 2.0 License](LICENSE)

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