How can I enable HTTPS for Dockerized .NET Blazor apps using DNS on a Linux server?

Below is a detailed recommendation addressing your questions:

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1. HTTPS Termination Approach

Recommended Approach: 1.2 – Use a Reverse Proxy (e.g., Nginx) on the Host

• Centralized Certificate Management:
  By handling SSL termination at the reverse proxy level, you simplify certificate management—you only need to install, renew, and update certificates in one place rather than in every container.

• Simpler Application Configuration:
  Your .NET Blazor containers can continue running on HTTP (port 80) internally. The reverse proxy handles decryption of the HTTPS traffic from clients and forwards plain HTTP to the appropriate container, reducing the complexity in the application code.

• Scalability and Maintainability:
  When adding, removing, or updating applications, only the reverse proxy configuration needs to be adjusted. This approach also lets you leverage robust features available in Nginx (or similar proxies) for load balancing, caching, and enhanced security.

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2. DNS and Certificate Challenges

• Certificate Domain Matching:
  Each DNS entry (such as application1.intra.contoso.de) must have a certificate that the internal CA issues for the corresponding domain.

  • You can obtain individual certificates for each domain, or use a multi-domain (SAN) certificate that covers all the relevant DNS names.

• Reverse Proxy Configuration:
  The reverse proxy must be configured to inspect the Host header so that it correctly routes requests based on the domain name. This ensures that the correct certificate is presented and the request is forwarded to the appropriate container.

• Internal Certificate Management:
  Since your certificates are provided internally:

  • Ensure your CA’s root certificate is trusted by client machines.
  • Automate or schedule timely renewals to avoid service interruptions.
  • Use proper certificate chain configuration to maintain validity.

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Example Nginx Configuration

Below is an example configuration snippet for Nginx that demonstrates how you might set up HTTPS termination and routing for one of your applications:

NGINXCopied
server {
    listen 443 ssl;
    server_name application1.intra.contoso.de;

    ssl_certificate             /etc/nginx/ssl/application1.intra.contoso.de.crt;
    ssl_certificate_key         /etc/nginx/ssl/application1.intra.contoso.de.key;
    ssl_protocols               TLSv1.2 TLSv1.3;
    ssl_ciphers                 HIGH:!aNULL:!MD5;

    location / {
        proxy_pass          http://127.0.0.1:8080;
        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 https;
    }
}

# Additional server blocks can be configured for application2.intra.contoso.de, etc.

Additional Considerations

• HTTP to HTTPS Redirection:
  You might also want to include a server block that listens on port 80 to redirect HTTP requests to HTTPS. For example:

  NGINXCopied
  server {
      listen 80;
      server_name application1.intra.contoso.de;
  
      return 301 https://$host$request_uri;
  }

• Internal Network Considerations:
  Since your applications are only accessible on the internal network, ensure that the internal CA is suitably configured and that there are no firewall or routing issues.

• Container Independence:
  With this proxy approach, your containers can remain unchanged with respect to HTTPS concerns. Only the reverse proxy handles SSL/TLS.

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Conclusion

• For HTTPS: Use a reverse proxy (like Nginx) on your host to terminate SSL, manage certificates, and route requests based on DNS (Host header).
• For Certificates: Ensure each DNS entry has a matching certificate (or use a multi-DNS certificate) and configure the reverse proxy accordingly.
• For Internal Deployment: This approach works well in an internal network context and allows you to keep your application URLs unchanged.

This setup offers clear benefits, simplifying both the application configuration and ongoing certificate management.