docs: kamaji-ingress-addon guide (#605)

Signed-off-by: Dario Tranchitella <dario@tranchitella.eu>

docs/content/enterprise-addons/index.md

@@ -0,0 +1,20 @@
+# Enterprise Addons
+
+This document contains the documentation of the available Kamaji addons. 
+
+## What is a Kamaji Addon
+
+A Kamaji Addon is a separate component installed in the same Kamaji cluster.
+It offers an additional set of features required for enterprise-grade usage.
+
+The developed Kamaji addons are closed-source available and work with the upstream Kamaji edition.
+
+## Distribution of Addons
+
+The Kamaji Addons are available behind an active [subscription license](https://clastix.io/support/).
+
+Once a subscription is activated, the [CLASTIX](https://clastix.io) team will automate the push of required OCI (container images) and Helm Chart artefacts to the customer's OCI-compatible repository.
+
+## Available addons
+
+- [Ingress Addon](/enterprise-addons/ingress): expose Tenant Control Planes behind an Ingress Controller to reduce the amount of required LoadBalancer services

docs/content/enterprise-addons/ingress.md

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+# Ingress Addon
+
+A Kubernetes API Server could be announced to users in several ways.
+The most preferred way is leveraging on Load Balancers with their dedicated IP.
+
+![Load Balancer setup](../images/kamaji-addon-ingress-lb.png#only-light)
+![Load Balancer setup](../images/kamaji-addon-ingress-lb-dark.png#only-dark)
+
+However, IPv4 addresses could be limited and scarce in availability, as well as expensive for public ones when running in the Cloud.
+A possible optimisation could be implementing an Ingress Controller which routes traffic to Kubernetes API Servers on a host-routing basis.
+
+Despite this solution sounding optimal for end users, it brings some challenges from the worker nodes' standpoint.
+
+## Challenges
+
+Internally deployed applications that need to interact with the Kubernetes API Server will leverage on the `kubernetes` endpoint in the `default` namespace:
+every request sent to the `https://kubernetes.default.svc` endpoint will be forwarded to the Kubernetes API Server.
+
+The routing put in place by the Kubernetes CNI is based on the L4, meaning that all the requests will be forwarded to the Ingress Controller with no `Host` header,
+making impossible a routing based on the FQDN.
+
+## Solution
+
+The `kamaji-addon-ingress` is an addon that will expose the Tenant Control Plane behind an Ingress Controller.
+It's responsible for creating an `Ingress` object with the required HTTP rules, as well as the annotations needed for the TLS/SSL passthrough.
+
+![Ingress Controller setup](../images/kamaji-addon-ingress-ic.png#only-light)
+![Ingress Controller setup](../images/kamaji-addon-ingress-ic-dark.png#only-dark)
+
+Following is the list of supported Ingress Controllers:
+
+- [HAProxy Technologies Kubernetes Ingress](https://github.com/haproxytech/kubernetes-ingress)
+
+> Active subscribers can request additional Ingress Controller flavours  
+
+## How to enable the Addon
+
+Annotate the Tenant Control Plane instances with the key `kamaji.clastix.io/ingress.domain` and the domain suffix domain value:
+
+```shell
+kubectl annotate tenantcontrolplane $NAME kamaji.clastix.io/ingress.domain=$SUFFIX_DOMAIN
+```
+
+The value must be the expected suffix domain of generated resources.
+
+```yaml
+apiVersion: kamaji.clastix.io/v1alpha1
+kind: TenantControlPlane
+metadata:
+  annotations:
+    kamaji.clastix.io/ingress.domain: clastix.cloud  # the expected kamaji-addon-ingress label
+  name: tenant-00
+  namespace: apezzuto
+```
+
+Once a Tenant Control Plane has been annotated with this key, the addon will generate the following `Ingress` object.
+
+```yaml
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  annotations:
+    haproxy.org/ssl-passthrough: "true"
+  name: 592ee7b8-cd07-48cf-b754-76f370c3f87c
+  namespace: apezzuto
+spec:
+  ingressClassName: haproxy
+  rules:
+  - host: apezzuto-tenant-00.k8s.clastix.cloud
+    http:
+      paths:
+      - backend:
+          service:
+            name: tenant-00
+            port:
+              number: 6443
+        path: /
+        pathType: Prefix
+  - host: apezzuto-tenant-00.konnectivity.clastix.cloud
+    http:
+      paths:
+      - backend:
+          service:
+            name: tenant-00
+            port:
+              number: 8132
+        path: /
+        pathType: Prefix
+```
+
+The pattern for the generated hosts is the following:
+`${tcp.namespace}-${tcp.name}.{k8s|konnectivity}.${ADDON_ANNOTATION_VALUE}`
+
+> Please, notice the `konnectivity` rule will be created only if the `konnectivity` addon has been enabled.
+
+## Infrastructure requirements
+
+For Tenant Control Plane objects leveraging on this addon, the following changes must be implemented.
+
+### Ingress Controller
+
+The Ingress Controller must be deployed to listen for `https` connection on the default port `443`:
+if you have different requirements, please, engage with the CLASTIX team.
+
+### DNS resolution
+
+The following zones must be configured properly according to your DNS provider:
+
+```
+*.konnectivity.clastix.cloud    A   <YOUR_INGRESS_CONTROLLER_IP>
+*.k8s.clastix.cloud             A   <YOUR_INGRESS_CONTROLLER_IP>
+```
+
+### Certificate SANs
+
+```yaml
+  networkProfile:
+    certSANs:
+    - apezzuto-tenant-00.k8s.clastix.cloud
+    - apezzuto-tenant-00.konnectivity.clastix.cloud
+    dnsServiceIPs:
+    - 10.96.0.10
+    podCidr: 10.244.0.0/16
+    port: 6443
+    serviceCidr: 10.96.0.0/16
+```
+
+### Service type and Ingress
+
+The Kubernetes API Server can be exposed using a `ClusterIP`, rather than a Load Balancer.
+
+```yaml
+spec:
+  controlPlane:
+    service:
+      serviceType: ClusterIP
+    ingress:
+      hostname: apezzuto-tenant-00.k8s.clastix.cloud:443
+      ingressClassName: unhandled
+```
+
+The `ingressClassName` value must match a non-handled `IngressClass` object,
+the addon will take care of generating the correct object.
+
+> Nota Bene: the `hostname` must absolutely point to the 443 port
+
+### Kubernetes components extra Arguments
+
+The Kubernetes API Server must start with the following flag:
+
+```yaml
+spec:
+  controlPlane:
+    deployment:
+      extraArgs:
+        apiServer:
+          - --endpoint-reconciler-type=none
+```
+
+The `kamaji-addon-ingress` will be responsible for populating the `kubernetes` EndpointSlice object in the Tenant cluster.
+
+If you're running with `konnectivity`, also this extra argument must be enforced:
+
+```yaml
+spec:
+  addons:
+    konnectivity:
+      agent:
+        extraArgs:
+        - --proxy-server-host=apezzuto-tenant-00.konnectivity.clastix.cloud
+        - --proxy-server-port=443
+```
+
+## Air-gapped environments
+
+The `kamaji-addon-ingress` works with a deployed component in the Tenant Cluster based on the container image `docker.io/clastix/tcp-proxy:latest`.
+
+The same image can be replaced by customising the Addon Helm value upon installation:
+
+```
+--set options.tcpProxyImage=private.repository.tld/tcp-proxy:latest
+```

docs/mkdocs.yml

@@ -77,4 +77,7 @@ nav:
   - reference/versioning.md
   - reference/api.md
 - 'Telemetry': telemetry.md
+- 'Enterprise Addons':
+  - enterprise-addons/index.md
+  - enterprise-addons/ingress.md
 - 'Contribute': contribute.md