feat: add ZeroTier for remote access

- Fully open source
- Has free hosted version (my.zerotier.com)
- Can be automated with Terraform
- Pretty good performance with UDP hole punching

README.md

@@ -47,6 +47,7 @@ More information can be found in [the roadmap](#roadmap) below.
 - [x] Modular architecture, easy to add or remove features/components
 - [x] Automated certificate management
 - [x] Automatically update DNS records for exposed services
+- [x] VPN
 - [x] Expose services to the internet securely with [Cloudflare Tunnel](https://www.cloudflare.com/products/tunnel/)
 - [x] CI/CD platform
 - [x] Private container registry
@@ -195,6 +196,11 @@ They can't capture all the project's features, but they are sufficient to get a
         <td><a href="https://www.vaultproject.io">Vault</a></td>
         <td>Secrets and encryption management system</td>
     </tr>
+    <tr>
+        <td><img width="32" src="https://docs.zerotier.com/img/ZeroTierIcon.png"></td>
+        <td><a href="https://zerotier.com">ZeroTier</a></td>
+        <td>VPN without port-forwarding</td>
+    </tr>
 </table>
 
 ## Get Started

docs/installation/production/external-resources.md

@@ -12,6 +12,7 @@ Below is a list of external resources and why we need them (also see some [alter
 | Terraform Cloud | Workspace       | Terraform state backend                                                                                                     |
 | Cloudflare      | DNS             | DNS and [DNS-01 challenge](https://letsencrypt.org/docs/challenge-types/#dns-01-challenge) for certificates                 |
 | Cloudflare      | Tunnel          | Public services to the internet without port-forwarding                                                                     |
+| ZeroTier        | Virtual network | Use as VPN to access home network from anywhere (with [UDP hole punching](https://en.wikipedia.org/wiki/UDP_hole_punching)) |
 <!-- | Minio           | Bucket     | Onsite backup                                                                                               | -->
 <!-- | AWS             | S3 Glacier | Offsite backup                                                                                              | -->
 
@@ -49,6 +50,11 @@ If you decide to use a [different Terraform backend](https://www.terraform.io/la
 <!-- └── Is in - 117.xxx.xxx.xxx, 2402:xxx:xxx:xxx:xxx:xxx:xxx:xxx -->
 <!-- ``` -->
 
+### ZeroTier
+
+- Create a ZeroTier account <https://my.zerotier.com>
+- Generate a new API Token at <https://my.zerotier.com/account>
+
 <!-- ### Create Minio keys -->
 
 <!-- TODO: skip this for now -->
@@ -59,7 +65,21 @@ If you decide to use a [different Terraform backend](https://www.terraform.io/la
 
 ## Alternatives
 
-- Terraform Cloud: any other [Terraform backends](https://www.terraform.io/language/settings/backends)
-- Cloudflare DNS: see [manual DNS setup](../../tutorials/manual-dns-setup.md)
-- Cloudflare Tunnel: you can create a small VPS in the cloud and utilize Wireguard and HAProxy to route traffic via it, or just use simple port-forwarding if it's available (see also [awesome tunneling](https://github.com/anderspitman/awesome-tunneling))
+To avoid vendor lock-in, each external provider must have an equivalent alternative that is easy to replace:
+
+- Terraform Cloud:
+    - Any other [Terraform backends](https://www.terraform.io/language/settings/backends)
+- Cloudflare DNS:
+    - Update cert-manager and external-dns to use a different provider
+    - [Manual DNS setup](../../tutorials/manual-dns-setup.md)
+- Cloudflare Tunnel:
+    - Use port-forwarding if it's available
+    - Create a small VPS in the cloud and utilize Wireguard and HAProxy to route traffic via it
+    - Access everything via VPN
+    - See also [awesome tunneling](https://github.com/anderspitman/awesome-tunneling)
+- ZeroTier virtual network:
+    - [Host your own ZeroTier](https://docs.zerotier.com/self-hosting/introduction)
+    - [Tailscale](https://tailscale.com) (closed source, but you can use [Headscale](https://github.com/juanfont/headscale) to host your own Tailscale control server)
+    - [Netmaker](https://www.netmaker.org) (there's no hosted version, you'll need to host your own server)
+    - Wireguard server (requires port-forwarding)
 <!-- - Minio and S3 Glacier: any S3 compatible object storage, such as Backblaze B2, Minio... -->

external/main.tf

@@ -4,3 +4,11 @@ module "cloudflare" {
   cloudflare_email      = var.cloudflare_email
   cloudflare_api_key    = var.cloudflare_api_key
 }
+
+module "zerotier" {
+  source                 = "./modules/zerotier"
+  zerotier_central_token = var.zerotier_central_token
+  bridged_routes = [
+    "192.168.1.0/24" # TODO add this to configure script
+  ]
+}

external/modules/zerotier/main.tf

@@ -0,0 +1,53 @@
+locals {
+  router_ip = cidrhost(var.managed_route, 1) # Use the second IP in the VPN subnet as the router
+}
+
+resource "zerotier_network" "network" {
+  name        = var.name
+  description = var.description
+  private     = true
+
+  route {
+    target = var.managed_route
+  }
+
+  dynamic "route" {
+    for_each = var.bridged_routes
+
+    content {
+      target = route.value
+      via    = local.router_ip
+    }
+  }
+
+  assignment_pool {
+    start = cidrhost(var.managed_route, 0)
+    end   = cidrhost(var.managed_route, -1)
+  }
+}
+
+resource "zerotier_identity" "router" {}
+
+resource "zerotier_member" "router" {
+  network_id              = zerotier_network.network.id
+  name                    = "router"
+  member_id               = zerotier_identity.router.id
+  allow_ethernet_bridging = true
+  no_auto_assign_ips      = true
+  ip_assignments = [
+    local.router_ip
+  ]
+}
+
+resource "kubernetes_secret" "router" {
+  metadata {
+    name      = "zerotier-router"
+    namespace = "zerotier"
+  }
+
+  data = {
+    ZEROTIER_NETWORK_ID      = zerotier_network.network.id
+    ZEROTIER_IDENTITY_PUBLIC = zerotier_identity.router.public_key
+    ZEROTIER_IDENTITY_SECRET = zerotier_identity.router.private_key
+  }
+}

external/modules/zerotier/variables.tf

@@ -0,0 +1,34 @@
+variable "zerotier_central_url" {
+  description = "ZeroTier Central API endpoint"
+  type        = string
+  default     = "https://my.zerotier.com/api" # https://github.com/zerotier/go-ztcentral/blob/4d397d1e82c043a5376789177ad55536044d69ce/client.go#L44
+}
+
+variable "zerotier_central_token" {
+  description = "ZeroTier Central API Token"
+  type        = string
+  sensitive   = true
+}
+
+variable "name" {
+  description = "Network name"
+  type        = string
+  default     = "homelab"
+}
+
+variable "description" {
+  description = "Network description"
+  type        = string
+  default     = "Homelab network"
+}
+
+variable "managed_route" {
+  description = "ZeroTier managed route"
+  type        = string
+  default     = "10.147.17.0/24"
+}
+
+variable "bridged_routes" {
+  description = "List of bridged routes" # TODO
+  type        = list(string)
+}

external/modules/zerotier/versions.tf

@@ -0,0 +1,13 @@
+terraform {
+  required_providers {
+    zerotier = {
+      source  = "zerotier/zerotier"
+      version = "~> 1.2.0"
+    }
+  }
+}
+
+provider "zerotier" {
+  zerotier_central_url   = var.zerotier_central_url
+  zerotier_central_token = var.zerotier_central_token
+}

external/namespaces.yml

@@ -12,3 +12,4 @@
         - external-dns
         - k8up-operator
         - tekton-pipelines
+        - zerotier

external/terraform.tfvars.j2

@@ -1,3 +1,4 @@
 cloudflare_email = "{{ cloudflare_email }}"
 cloudflare_api_key = "{{ cloudflare_api_key }}"
 cloudflare_account_id = "{{ cloudflare_account_id }}"
+zerotier_central_token = "{{ zerotier_central_token }}"

external/tfvars.yml

@@ -9,6 +9,8 @@
     - name: cloudflare_account_id
       prompt: Enter Cloudflare account ID
       private: false
+    - name: zerotier_central_token
+      prompt: Enter ZeroTier Central API Token
   tasks:
     - name: Render environment file
       template:

external/variables.tf

@@ -10,3 +10,7 @@ variable "cloudflare_api_key" {
 variable "cloudflare_account_id" {
   type = string
 }
+
+variable "zerotier_central_token" {
+  type = string
+}

platform/zerotier/deployment.yaml

@@ -0,0 +1,65 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: zerotier-router
+  namespace: zerotier
+  labels:
+    app: zerotier-router
+spec:
+  selector:
+    matchLabels:
+      app: zerotier-router
+  replicas: 1
+  template:
+    metadata:
+      labels:
+        app: zerotier-router
+    spec:
+      containers:
+        - name: zerotier-router
+          image: zerotier/zerotier:latest  # TODO use tag
+          command:
+            - "sh"
+            - "-c"
+          args: # TODO optimize this
+            - |
+              # TODO install this on upstream image?
+              apt-get install -y iptables
+
+              # TODO is there a better way to get the interface name?
+              export PHY_IFACE="$(ip route | grep ${POD_IP} | cut -d ' ' -f 3)"
+              export ZT_IFACE=zt0
+
+              # Override the default random interface name
+              mkdir -p /var/lib/zerotier-one
+              echo "${ZEROTIER_NETWORK_ID}=${ZT_IFACE}" >> /var/lib/zerotier-one/devicemap
+
+              iptables -t nat -A POSTROUTING -o $PHY_IFACE -j MASQUERADE
+              iptables -A FORWARD -i $PHY_IFACE -o $ZT_IFACE -m state --state RELATED,ESTABLISHED -j ACCEPT
+              iptables -A FORWARD -i $ZT_IFACE -o $PHY_IFACE -j ACCEPT
+
+              /entrypoint.sh "${ZEROTIER_NETWORK_ID}"
+          resources:
+            requests:
+              cpu: 100m
+              memory: 128Mi
+          env:
+            - name: POD_IP
+              valueFrom:
+                fieldRef:
+                  fieldPath: status.podIP
+          envFrom:
+            - secretRef:
+                name: zerotier-router
+          securityContext:
+            capabilities:
+              add:
+                - NET_ADMIN
+          volumeMounts:
+            - name: dev-net-tun
+              mountPath: /dev/net/tun
+      volumes:
+        - name: dev-net-tun
+          hostPath:
+            path: /dev/net/tun
+            type: CharDevice

platform/zerotier/kustomization.yaml

@@ -0,0 +1,5 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - deployment.yaml