---
title: "Setting Up IIS as a Load Balancer for OPC Servers"
slug: "high-availability-iis-reverse-proxy-cloudflare-tunnel-setup-opc-servers"
updated: 2026-05-26T13:22:41Z
published: 2026-05-26T13:22:41Z
canonical: "help.scalefusion.com/high-availability-iis-reverse-proxy-cloudflare-tunnel-setup-opc-servers"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://help.scalefusion.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Setting Up IIS as a Load Balancer for OPC Servers

This guide explains how to configure High Availability (HA) for On-Prem Connector (OPC) using Microsoft IIS as a reverse proxy and load balancer. With this setup, IIS distributes traffic between multiple OPC servers, helping improve reliability and reduce downtime if one server becomes unavailable.

> [!CAUTION]
> **Note:** This document is intended as a general setup guide and covers only the specific configuration steps. Steps may vary depending on software versions, environment settings, or future updates. Scalefusion does not provide technical support for third-party software or infrastructure configurations referenced in this document.
> 
> Any tools or software mentioned are shared for guidance purposes only, and customers should choose the approach best suited to their environment.

**Overview**

- Configure IIS as a load balancer for OPC
- Set up Cloudflare Tunnel for secure external access
- Route traffic to multiple OPC servers
- Configure health checks and failover support

**The Traffic Flow:**

1. User connects to the Cloudflare website.
2. Cloudflare sends traffic to our IIS Load Balancer via a secure tunnel.
3. The IIS Load Balancer checks which backend server is healthy and forwards the request to it on port **28767**, keeping the exact URL path intact.

## SERVER INVENTORY

| Server Name | IP Address | Role |
| --- | --- | --- |
| **OPC Machine 1** | `192.168.14.157` | OPC Server 1 (Listens on port 28767) |
| **OPC Machine 2** | `192.168.14.217` | OPC Server 2 (Listens on port 28767) |
| **Load Balancer** | `192.168.14.182` | IIS Reverse Proxy & Cloudflare Tunnel |

## PHASE 1 | INSTALL CLOUDFLARE TUNNEL (ON LOAD BALANCER)

*This step securely connects your local IIS server to the public Cloudflare network without opening firewall ports.*

1. Log into the **Load Balancer Server** (`192.168.14.182`).
2. Open a web browser and download the Cloudflare installer: [Download Link](https://github.com/cloudflare/cloudflared/releases/latest/download/cloudflared-windows-amd64.msi)
3. Run the downloaded `.msi` file to install it.
4. Click the Windows Start menu, type **cmd**, right-click **Command Prompt**, and select **Run as Administrator**.
5. Copy your specific tunnel token from the Cloudflare Dashboard and run this command: `cloudflared.exe service install <Your-Token-Here>`
6. The service will start automatically in the background.

## PHASE 2 | INSTALL IIS & REQUIRED MODULES

*We need to install the web server and the special Microsoft add-ons that allow it to act as a load balancer.*

1. On the Load Balancer, open **Server Manager** and install the **Web Server (IIS)** role.
2. Open a web browser and download/install these two official Microsoft extensions:
  - **Application Request Routing (ARR) 3.0**
  - **URL Rewrite Module 2.1**
3. Once both are installed, close and reopen the **IIS Manager** so the new features appear.

## PHASE 3 | TURN ON THE GLOBAL PROXY

*If we don't flip this switch, IIS will look for local files instead of forwarding traffic.*

1. Open **IIS Manager**.
2. Click on the very top server name in the left-hand menu (e.g., `OPC-IIS-HA`).
3. In the middle screen, double-click **Application Request Routing Cache**.
4. In the right-hand menu, click **Server Proxy Settings...**
5. Check the very top box that says **Enable proxy**.
6. Click **Apply** in the top right corner.

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-I651DZG1.png)

## PHASE 4 | CREATE THE SERVER FARM & FIX THE PORTS

*Here we tell IIS exactly where our two backend servers live.*

1. In the left menu of IIS Manager, right-click **Server Farms** and choose **Create Server Farm...**
2. Name it `OPC_Farm` and click **Next**.
3. Type the IP of Server 1 (`192.168.14.157`) and click **Add**.
4. Type the IP of Server 2 (`192.168.14.217`) and click **Add**.
5. Click **Finish**.
6. A box will pop up asking: *"IIS can automatically create a URL rewrite rule..."*. Click **Yes**.

**If You Not get the Rule Already created follow below :**
  - **Go to server Farm → Routing rules > check the Use URL Rewrite box**

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-4KPK0IA0.png)

**IMPORTANT**: Fixing the Custom Port (28767)

*The IIS screen has a bug that sometimes ignores custom ports. We will type it straight into the configuration file to guarantee it works.*

1. Open **Notepad** as an Administrator.
2. Go to `File` -> `Open` and navigate to: `C:\Windows\System32\inetsrv\config\`
3. Change the file type in the bottom right from "Text Documents" to **All Files (*.*)**.
4. Open `applicationHost.config`.
5. Press `Ctrl + F` and search for `<webFarm name="OPC_Farm">`.
6. Add `httpPort="28767"` to the `<applicationRequestRouting>` line under both servers. It must look exactly like the image below.
7. Save and close Notepad.

**Before Changes**

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-83LQ4EMI.png)

**After Changes**

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-3MDG0SH9.png)

## PHASE 5 | FIX THE ROUTING RULE (URL REWRITE)

*The automatic rule IIS created deletes the end of our URLs (like* `/opc/heart-beat`*). We must fix the rule to pass the full URL to the backends.*

1. In IIS Manager, click the top server name in the left menu again.
2. Double-click **URL Rewrite**.
3. Double-click the rule named `ARR_OPC_Farm_loadbalance`.
4. Change the settings to exactly match the following:
  - **Using:** Wildcards
  - **Pattern:** `(*)`
  - **Action type:** Route to Server Farm
  - **Action Path:** `/{R:1}`
5. Click **Apply** in the top right corner.

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-DE2ONXHV.png)

## PHASE 6 | CONFIGURE HEALTH CHECKS

*This tells IIS to stop sending traffic to a server if it crashes or reboots.*

1. In IIS Manager, expand **Server Farms** and click `OPC_Farm`.
2. Double-click **Health Test**.
3. Enter the following URL: `http://192.168.14.157:28767/opc/heart-beat` *(Update the path if your specific heartbeat endpoint is different)*.
4. Set the Interval and Timeout to **30 seconds**.
5. Type **OK** in the "Response match" box.
6. Click **Apply**.

## PHASE 7 | FINAL RESTART AND VERIFICATION

*We must restart IIS completely to lock in the Notepad file changes.*

1. Open **Command Prompt** as Administrator.
2. Type `iisreset` and press Enter.
3. Once the service restarts, open a web browser.
4. Type in your public Cloudflare URL (e.g., `https://your-domain.com/opc/heart-beat`[).](https://your-domain.com/opc/heart-beat).)

![](https://cdn.document360.io/175c0eac-012f-4410-bdc5-ac60794f82d8/Images/Documentation/image-KUVRNXMC.png)
5. If the page loads successfully, the Cloudflare Tunnel is catching the traffic, handing it to IIS, and IIS is successfully balancing it across your two backend servers on port 28767!