dev-docs: full L3 connectivity in VPN chart

dev-docs/howto/vpn/helm/README.md

@@ -2,21 +2,39 @@
 
 This Helm chart deploys a VPN server to your Constellation cluster.
 
-## Installation
+## Prerequisites
 
-1. Create and populate the configuration.
+* Constellation >= v2.14.0
+* A publicly routable VPN endpoint on premises that supports IPSec in IKEv2
+  tunnel mode with NAT traversal enabled.
+* A list of on-prem CIDRs that should be reachable from Constellation.
+
+## Setup
+
+1. Configure Cilium to route services for the VPN (see [Architecture](#architecture) for details).
+   * Edit the Cilium config: `kubectl -n kube-system edit configmap cilium-config`.
+   * Set the config item `enable-sctp: "true"`.
+   * Restart the Cilium agents: `kubectl -n kube-system rollout restart daemonset/cilium`.
+
+2. Create the Constellation VPN configuration file.
 
    ```sh
    helm inspect values . >config.yaml
    ```
 
-2. Install the Helm chart.
+3. Populate the Constellation VPN configuration file. At least the following
+   need to be configured:
+   * The list of on-prem CIDRs (`peerCIDRs`).
+   * The `ipsec` subsection.
+
+4. Install the Helm chart.
 
    ```sh
    helm install -f config.yaml vpn . 
    ```
 
-3. Follow the post-installation instructions displayed by the CLI.
+5. Configure the on-prem gateway with Constellation's pod and service CIDR
+   (see `config.yaml`).
 
 ## Things to try
 
@@ -32,19 +50,35 @@ Ask the Kubernetes API server about its wellbeing:
 curl --insecure https://10.96.0.1:6443/healthz
 ```
 
+Ping a pod:
+
+```sh
+ping $(kubectl get pods vpn-frontend-0 -o go-template --template '{{ .status.podIP }}')
+```
+
 ## Architecture
 
-The VPN server is deployed as a `StatefulSet` to the cluster. It hosts the VPN frontend component, which is responsible for relaying traffic between the pod and the on-prem network, and the routing components that provide access to Constellation resources. The frontend supports IPSec and Wireguard.
+The VPN server is deployed as a `StatefulSet` to the cluster. It hosts the VPN
+frontend component, which is responsible for relaying traffic between the pod
+and the on-prem network over an IPSec tunnel.
+
+The VPN frontend is exposed with a public LoadBalancer so that it becomes
+accessible from the on-prem network.
 
-The VPN frontend is exposed with a public LoadBalancer to be accessible from the on-prem network. Traffic that reaches the VPN server pod is split into two categories: pod IPs and service IPs.
+An init container sets up IP routes on the frontend host and inside the
+frontend pod. All routes are bound to the frontend pod's lxc interface and thus
+deleted together with it.
 
-The pod IP range is NATed with an iptables rule. On-prem worklaods can establish connections to a pod IP, but the Constellation workloads will see the client IP translated to that of the VPN frontend pod.
+A VPN operator deployment is added that configures the `CiliumEndpoint` with
+on-prem IP ranges, thus configuring routes on non-frontend hosts. The endpoint
+shares the frontend pod's lifecycle.
 
-The service IP range is handed to a transparent proxy running in the VPN frontend pod, which relays the connection to a backend pod. This is necessary because of the load-balancing mechanism of Cilium, which assumes service IP traffic to originate from the Constellation cluster itself. As for pod IP ranges, Constellation pods will only see the translated client address.
+In Cilium's default configuration, service endpoints are resolved in cgroup
+eBPF hooks that are not applicable to VPN traffic. We force Cilium to apply
+service NAT at the LXC interface by enabling SCTP support.
 
 ## Limitations
 
-* Service IPs need to be proxied by the VPN frontend pod. This is a single point of failure, and it may become a bottleneck.
-* IPs are NATed, so the Constellation pods won't see the real on-prem IPs.
-* NetworkPolicy can't be applied selectively to the on-prem ranges.
-* No connectivity from Constellation to on-prem workloads.
+* VPN traffic is handled by a single pod, which may become a bottleneck.
+* Frontend pod restarts / migrations invalidate IPSec connections.
+* Only pre-shared key authentication is supported.

dev-docs/howto/vpn/helm/files/operator/entrypoint.sh

@@ -0,0 +1,46 @@
+#!/bin/sh
+
+signaled() {
+  exit 143
+}
+
+trap signaled INT TERM
+
+all_ips() {
+  kubectl get pods "${VPN_FRONTEND_POD}" -o go-template --template '{{ range .status.podIPs }}{{ printf "%s " .ip }}{{ end }}'
+  echo "${VPN_PEER_CIDRS}"
+}
+
+cep_patch() {
+  for ip in $(all_ips); do printf '{"ipv4": "%s"}' "${ip}"; done | jq -s -c -j |
+    jq '[{op: "replace", path: "/status/networking/addressing", value: . }]'
+}
+
+# Format the space-separated CIDRs into a JSON array.
+vpn_cidrs=$(for ip in ${VPN_PEER_CIDRS}; do printf '"%s" ' "${ip}"; done | jq -s -c -j)
+
+masq_patch() {
+  kubectl -n kube-system get configmap ip-masq-agent -o json |
+    jq -r .data.config |
+    jq "{ masqLinkLocal: .masqLinkLocal, nonMasqueradeCIDRs: ((.nonMasqueradeCIDRs - ${vpn_cidrs}) + ${vpn_cidrs}) }" |
+    jq '@json | [{op: "replace", path: "/data/config", value: . }]'
+}
+
+reconcile_masq() {
+  if ! kubectl -n kube-system get configmap ip-masq-agent > /dev/null; then
+    # We don't know enough to create an ip-masq-agent.
+    return 0
+  fi
+
+  kubectl -n kube-system patch configmap ip-masq-agent --type json --patch "$(masq_patch)" > /dev/null
+}
+
+while true; do
+  # Reconcile CiliumEndpoint to advertise VPN CIDRs.
+  kubectl patch ciliumendpoint "${VPN_FRONTEND_POD}" --type json --patch "$(cep_patch)" > /dev/null
+
+  # Reconcile ip-masq-agent configuration to exclude VPN traffic.
+  reconcile_masq
+
+  sleep 10
+done

dev-docs/howto/vpn/helm/files/strongswan/sidecar.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+
+set -u
+
+if [ "$$" -eq "1" ]; then
+  echo 'This script must run in the root PID namespace, but $$ == 1!' >&2
+  exit 1
+fi
+
+myip() {
+  ip -j addr show eth0 | jq -r '.[0].addr_info[] | select(.family == "inet") | .local'
+}
+
+# Disable source IP verification on our network interface. Otherwise, VPN
+# packets will be dropped by Cilium.
+reconcile_sip_verification() {
+  # We want all of the cilium calls in this function to target the same
+  # process, so that we fail if the agent restarts in between. Thus, we only
+  # query the pid once per reconciliation.
+  cilium_agent=$(pidof cilium-agent) || return 0
+
+  cilium() {
+    nsenter -t "${cilium_agent}" -a -r -w cilium "$@"
+  }
+
+  myendpoint=$(cilium endpoint get "ipv4:$(myip)" | jq '.[0].id') || return 0
+
+  if [ "$(cilium endpoint config "${myendpoint}" -o json | jq -r .realized.options.SourceIPVerification)" = "Enabled" ]; then
+    cilium endpoint config "${myendpoint}" SourceIPVerification=Disabled
+  fi
+}
+
+# Set up the route from the node network namespace to the VPN pod.
+reconcile_route() {
+  for cidr in ${VPN_PEER_CIDRS}; do
+    nsenter -t 1 -n ip route replace "${cidr}" via "$(myip)"
+  done
+}
+
+while true; do
+  reconcile_route
+  reconcile_sip_verification
+  sleep 10
+done

dev-docs/howto/vpn/helm/templates/_helpers.tpl

@@ -37,4 +37,6 @@ app.kubernetes.io/instance: {{ .Release.Name }}
   value: {{ .Values.podCIDR | quote }}
 - name: VPN_SERVICE_CIDR
   value: {{ .Values.serviceCIDR | quote }}
+- name: VPN_FRONTEND_POD
+  value: {{ include "..fullname" . }}-frontend-0
 {{- end }}

dev-docs/howto/vpn/helm/templates/configmaps.yaml

@@ -1,27 +1,15 @@
 apiVersion: v1
 kind: ConfigMap
 metadata:
-  name: {{ include "..fullname" . }}-tproxy
+  name: {{ include "..fullname" . }}-operator
   labels: {{- include "..labels" . | nindent 4 }}
 data:
-{{ (.Files.Glob "files/tproxy-setup.sh").AsConfig | indent 2 }}
+{{ (.Files.Glob "files/operator/*").AsConfig | indent 2 }}
 ---
-{{- if .Values.wireguard.enabled }}
-apiVersion: v1
-kind: ConfigMap
-metadata:
-  name: {{ include "..fullname" . }}-wg
-  labels: {{- include "..labels" . | nindent 4 }}
-data:
-{{ (.Files.Glob "files/wireguard-setup.sh").AsConfig | indent 2 }}
-{{- end }}
----
-{{ if .Values.ipsec.enabled }}
 apiVersion: v1
 kind: ConfigMap
 metadata:
   name: {{ include "..fullname" . }}-strongswan
   labels: {{- include "..labels" . | nindent 4 }}
 data:
 {{ (.Files.Glob "files/strongswan/*").AsConfig | indent 2 }}
-{{- end }}

dev-docs/howto/vpn/helm/templates/operator-deployment.yaml

@@ -0,0 +1,32 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{ include "..fullname" . }}-operator
+  labels: {{- include "..labels" . | nindent 4 }}
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      {{- include "..selectorLabels" . | nindent 6 }}
+      component: operator
+  template:
+    metadata:
+      labels:
+        {{- include "..selectorLabels" . | nindent 8 }}
+        component: operator
+    spec:
+      serviceAccountName: {{ include "..fullname" . }}
+      automountServiceAccountToken: true
+      containers:
+      - name: operator
+        image: {{ .Values.image | quote }}
+        command: ["sh", "/scripts/entrypoint.sh"]
+        env: {{- include "..commonEnv" . | nindent 10 }}
+        volumeMounts:
+        - name: scripts
+          mountPath: "/scripts"
+          readOnly: true
+      volumes:
+      - name: scripts
+        configMap:
+          name: {{ include "..fullname" . }}-operator

dev-docs/howto/vpn/helm/templates/rbac.yaml

@@ -0,0 +1,33 @@
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: {{ include "..fullname" . }}
+automountServiceAccountToken: false
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: {{ include "..fullname" . }}
+rules:
+- apiGroups: [""]
+  resources: ["pods"]
+  verbs: ["get"]
+- apiGroups: [""]
+  resources: ["configmaps"]
+  verbs: ["get", "patch"]
+- apiGroups: ["cilium.io"]
+  resources: ["ciliumendpoints"]
+  verbs: ["get", "patch"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: {{ include "..fullname" . }}
+subjects:
+- kind: ServiceAccount
+  name: {{ include "..fullname" . }}
+  namespace: {{ .Release.Namespace }}
+roleRef:
+  kind: ClusterRole
+  name: {{ include "..fullname" . }}
+  apiGroup: rbac.authorization.k8s.io

dev-docs/howto/vpn/helm/templates/secrets.yaml

@@ -1,15 +1,3 @@
-{{- if .Values.wireguard.enabled }}
-apiVersion: v1
-kind: Secret
-metadata:
-  name: {{ include "..fullname" . }}-wg
-  labels:
-    {{- include "..labels" . | nindent 4 }}
-data:
-  wg.conf: {{ include "wireguard.conf" . | b64enc }}
-{{- end }}
----
-{{ if .Values.ipsec.enabled }}
 apiVersion: v1
 kind: Secret
 metadata:
@@ -18,4 +6,3 @@ metadata:
     {{- include "..labels" . | nindent 4 }}
 data:
   swanctl.conf: {{ include "strongswan.swanctl-conf" . | b64enc }}
-{{- end }}

dev-docs/howto/vpn/helm/templates/service.yaml

@@ -11,16 +11,9 @@ spec:
     component: frontend
   externalTrafficPolicy: Local
   ports:
-    {{- if .Values.ipsec.enabled }}
     - name: isakmp
       protocol: UDP
       port: 500
     - name: ipsec-nat-t
       protocol: UDP
       port: 4500
-    {{- end }}
-    {{- if .Values.wireguard.enabled }}
-    - name: wg
-      protocol: UDP
-      port: {{ .Values.wireguard.port }}
-    {{- end }}