SSL Certificate Multi-Domain Support: Adding blog.agentthread.dev

Overview

Extended the SSL certificate for blog.fcoinfup.com to support the blog.agentthread.dev domain, allowing both domains to use the same certificate.

Background

Created the blog.agentthread.dev domain through Cloudflare and connected it to the same server as blog.fcoinfup.com (130.162.133.47). To serve identical content on both domains, the SSL certificate was extended to support multiple domains.

Work Details

1. DNS Configuration

Cloudflare DNS Record Creation:

blog.agentthread.dev → 130.162.133.47 (A record)

Existing Domain:

blog.fcoinfup.com → CNAME → oci-yarang-ec1.fcoinfup.com → 130.162.133.47

2. SSL Certificate Extension

Existing Certificate Info:

Certificate Name: blog.fcoinfup.com
Domain: blog.fcoinfup.com (single domain)
Encryption: ECDSA
Expiration: 2026-06-08

Extended Certificate Info:

Certificate Name: blog.fcoinfup.com
Domains: blog.fcoinfup.com, blog.agentthread.dev
Encryption: ECDSA
Expiration: 2026-06-08 (89 days remaining)

3. Certbot Commands

Certificate Extension:

sudo certbot certonly --expand -d blog.fcoinfup.com -d blog.agentthread.dev

Or renew existing certificate:

sudo certbot renew --force-renewal --cert-name blog.fcoinfup.com

4. Nginx Configuration Update

Update server_name directive:

server {
    listen 443 ssl http2;
    server_name blog.fcoinfup.com blog.agentthread.dev;

    ssl_certificate /etc/letsencrypt/live/blog.fcoinfup.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/blog.fcoinfup.com/privkey.pem;

    # Other settings...
}

Reload Nginx:

sudo nginx -t      # Test configuration
sudo systemctl reload nginx

Technical Details

SSL/TLS Certificate

Type: ECDSA (Elliptic Curve Digital Signature Algorithm)
CA: Let’s Encrypt
SAN (Subject Alternative Name): blog.fcoinfup.com, blog.agentthread.dev
Expiration: 2026-06-08

Web Server

Software: nginx
HTTP→HTTPS Redirect: Automatic redirect enabled
HTTP/2: Enabled

DNS

Provider: Cloudflare
Record Type: A
TTL: 3600 seconds (1 hour)
Proxy: Disabled (DNS only)

Results

Accessible URLs

Both domains are accessible via HTTPS:

https://blog.fcoinfup.com ✅
https://blog.agentthread.dev ✅

HTTP Automatic Redirect

http://blog.fcoinfup.com     → https://blog.fcoinfup.com
http://blog.agentthread.dev  → https://blog.agentthread.dev

SSL Verification

$ curl -I https://blog.agentthread.dev
HTTP/2 200
server: nginx
content-type: text/html

Auto-Renewal

Let’s Encrypt certificates automatically renew every 90 days. The Certbot timer handles renewal automatically.

Check Renewal Status:

sudo systemctl status certbot.timer
sudo certbot renew --dry-run

Security Recommendations

Regular certificate expiration checks
HTTP security headers configuration (HSTS, CSP, etc.)
Strong encryption curves (currently using ECDSA)
Regular web server updates

Conclusion

The blog.agentthread.dev domain has been successfully added, and secure HTTPS access is available through a valid SSL certificate. Both domains serve identical content, allowing users to choose their preferred domain for access.

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