Introduction
Reverse proxies are essential in modern web architectures, especially for isolating backend services and enforcing security. However, SSL certificate issues can introduce complex challenges, particularly when dealing with HTTPS-only bindings, self-signed certificates, or organisational constraints. This blog shares practical insights from real-world troubleshooting, lab simulations, and customer scenarios.
Reverse Proxy Configuration: HTTP vs HTTPS Bindings
HTTP Binding Setup
In one scenario, I configured a reverse proxy for a backend site using HTTP binding on a custom port (e.g., 82). This setup is straightforward and avoids SSL complications. The reverse proxy helps prevent direct public access to the backend server, enhancing security.
HTTPS Binding Challenges
When the backend site is configured with only HTTPS binding (e.g., port 49494), the reverse proxy must validate the SSL certificate. This introduces challenges, especially with self-signed or privately issued certificates. In such cases, clients may encounter 502.3 - Bad Gateway errors due to failed certificate validation.
Certificate Issues and Solutions
Certificate Warnings
Accessing the reverse proxy site over HTTPS often led to browser warnings due to untrusted certificates. This is common when the backend uses a self-signed certificate or one issued by a private CA.
Solution 1: Root Certificate Installation
Installing the backend server’s root certificate on the reverse proxy server resolved the warning. This approach is secure and recommended for production environments.
Solution 2: Registry Change (Temporary)
For testing or constrained environments, I used a registry key to bypass certificate validation:
[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\IIS Extensions\\Application Request Routing\\Parameters]
"SecureConnectionIgnoreFlags"=dword:00003100
⚠️ This is a temporary workaround and should not be used in production due to security risks.
Troubleshooting Tips
- Always verify the backend URL directly from the proxy server.
- Use freb logs to identify SSL handshake failures.
- Monitor for 502.3 errors and correlate with certificate validation logs.
Lab Setup Guide
Prerequisites
- Reverse Proxy Server (Windows Server)
- Backend Server (Windows Server)
- Client Machine (Windows 10/11)
Backend Server
- Create a website with HTTP (e.g. port 82) and HTTPS (e.g. port 49494) bindings.
- Use self-signed or test certificates for HTTPS.
Reverse Proxy Server
- Configure URL rewrite rules for both HTTP and HTTPS.
- Test access to backend URLs from the proxy server.
- Import root certificates or apply registry changes as needed.
Client Machine
- Access the reverse proxy URL and validate connectivity.
- Observe browser behaviour and error messages.
Conclusion
SSL certificate issues in reverse proxy setups can be complex but manageable with the right approach. Whether you're dealing with HTTP/HTTPS bindings, self-signed certificates, or organisational constraints, understanding the root cause and applying targeted solutions is key. Collaboration, testing, and documentation are your best allies.
Microsoft