Networking Setup

Overview

This document details the network architecture used to securely expose the OpenStack infrastructure (INF1 and INF2) and the mail server using SSH reverse tunnels and NGINX reverse proxies. A VPS acts as a public gateway to forward traffic from the internet to internal services running on private networks.

SSH Reverse Tunnel: Mail Server Exposure (INF1 Controller)

The Mailcow mail server runs inside the INF1 controller node on a private network. To expose SMTP, SMTPS, IMAPS, and POP3S services externally, an SSH reverse tunnel is created from the INF1 controller node to the VPS (92.222.178.88):

ssh -fN -o ServerAliveInterval=60 \
  -R 2525:localhost:25 \
  -R 2587:localhost:587 \
  -R 2465:localhost:465 \
  -R 2993:localhost:993 \
  -R 2995:localhost:995 \
  ubuntu@92.222.178.88

Ports correspond to standard mail services:

SMTP: 25, 587 (submission)
SMTPS: 465
IMAPS: 993
POP3S: 995

The ServerAliveInterval=60 option helps keep the tunnel alive.
The -fN options run SSH in the background without opening a shell.

Port Forwarding on VPS for Mail Server

To map public-facing mail ports on the VPS to the tunneled ports, socat listeners are set up:

sudo socat TCP-LISTEN:587,fork,reuseaddr TCP:localhost:2587 &     # SMTP (submission)
sudo socat TCP-LISTEN:465,fork,reuseaddr TCP:localhost:2465 &     # SMTPS
sudo socat TCP-LISTEN:993,fork,reuseaddr TCP:localhost:2993 &     # IMAPS
sudo socat TCP-LISTEN:995,fork,reuseaddr TCP:localhost:2995 &     # POP3S

These allow external clients to connect securely to the mail services hosted inside the private network.

SSH Reverse Tunnel: OpenStack Services Exposure

To expose OpenStack services running on INF1 and INF2 securely through the VPS, reverse SSH tunnels are established from the VPS back to the internal hosts:

ssh -fN \
  -R 56080:172.20.20.241:6080 \  # Horizon
  -R 58774:localhost:8774 \      # Nova API
  -R 58778:localhost:8778 \      # Nova API
  -R 59292:localhost:9292 \      # Glance
  -R 5500:localhost:5000 \       # Keystone
  -R 59696:localhost:9696 \      # Neutron
  -R 58776:localhost:8776 \      # Nova API
  -R 58443:localhost:443 \       # HTTPS Proxy
  -R 58000:localhost:8000 \      # Magnum API
  -R 58004:localhost:8004 \      # Heat API
  ubuntu@92.222.178.88

Updated mapping for OpenStack services:

Tunnel Port	Service	Internal Port
5500	Keystone	5000
58774	Nova API	8774
58776	Nova API	8776
58778	Nova API	8778
59292	Glance API	9292
56080	Horizon (VNC)	6080
59696	Neutron API	9696
58443	HTTPS Proxy	443
58000	Magnum API	8000
58004	Heat API	8004

NGINX Reverse Proxy Configuration on VPS

NGINX acts as the TLS termination point and reverse proxy for incoming requests, forwarding them to tunneled ports.

Mail Server Proxy (mail.ulmexa.com)

server {
    listen 80;
    server_name mail.ulmexa.com;

    root /var/www/html;
    index index.html;

    location /.well-known/acme-challenge/ {
        allow all;
    }

    location / {
        return 404;
    }
}

server {
    listen 443 ssl;
    server_name mail.ulmexa.com;

    ssl_certificate /etc/letsencrypt/live/mail.ulmexa.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mail.ulmexa.com/privkey.pem;

    location / {
        proxy_pass http://<k8s-mailu-ip>:80;  # Kubernetes Mailu service IP
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

OpenStack Proxy (openstack.ulmexa.com)

Example for Keystone service:

server {
    listen 5000 ssl;
    server_name openstack.ulmexa.com;

    ssl_certificate /etc/letsencrypt/live/openstack.ulmexa.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/openstack.ulmexa.com/privkey.pem;

    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers HIGH:!aNULL:!MD5;

    location / {
        proxy_pass https://localhost:5500/;  # Tunnel endpoint
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Other OpenStack APIs (Nova, Glance, Neutron, Horizon, Magnum, Heat) are exposed on their respective ports with similar proxy blocks.

Summary Table of Ports and Services

Service	Internal Host/Port	VPS Tunnel Port	Public Access URL
Mailcow SMTP	INF1 Controller: 25, 587	2525, 2587	mail.ulmexa.com:587
Mailcow SMTPS	INF1 Controller: 465	2465	mail.ulmexa.com:465
Mailcow IMAPS	INF1 Controller: 993	2993	mail.ulmexa.com:993
Mailcow POP3S	INF1 Controller: 995	2995	mail.ulmexa.com:995
Keystone	INF1/INF2: 5000	5500	openstack.ulmexa.com:5000
Nova API	INF1/INF2: 8774, 8776, 8778	58774, 58776, 58778	openstack.ulmexa.com:8774, 8776, 8778
Glance API	INF1/INF2: 9292	59292	openstack.ulmexa.com:9292
Horizon (VNC)	INF1/INF2: 6080	56080	openstack.ulmexa.com:6080
Neutron API	INF1/INF2: 9696	59696	openstack.ulmexa.com:9696
Magnum API	INF1/INF2: 8000	58000	openstack.ulmexa.com:8000
Heat API	INF1/INF2: 8004	58004	openstack.ulmexa.com:8004

Network Flow Visual

Network Flow

Overview​

SSH Reverse Tunnel: Mail Server Exposure (INF1 Controller)​

Port Forwarding on VPS for Mail Server​

SSH Reverse Tunnel: OpenStack Services Exposure​

NGINX Reverse Proxy Configuration on VPS​

Mail Server Proxy (mail.ulmexa.com)​

OpenStack Proxy (openstack.ulmexa.com)​

Summary Table of Ports and Services​

Network Flow Visual​