nginx-ssl-cert-monitor is a lightweight Python tool that inspects all HTTPS-enabled virtual hosts configured in Nginx and checks the expiration status of their SSL/TLS certificates.

It automatically extracts active server_name entries from nginx -T, connects to each domain over TLS, retrieves the certificate, and calculates the remaining validity period.

The tool is designed for sysadmins and DevOps engineers who want a fast, dependency-light way to monitor certificate expiration across multiple Nginx sites without external monitoring systems.

🔧 Features

• Auto-detects SSL-enabled domains from Nginx configuration (nginx -T)
• Connects directly to each domain over TLS and reads the certificate
• Calculates days until expiration
• Supports warning and critical thresholds
• Colored CLI output for human readability
• JSON output for automation / CI / monitoring tools
• Exit codes compatible with monitoring systems (Nagios-style)

🚨 Exit codes

• 0 → All certificates OK
• 1 → At least one WARNING (near expiration)
• 2 → At least one CRITICAL (very close to expiration)
• 3 → At least one expired certificate

⚙️ Requirements

• Python 3.9+
• cryptography library
• Nginx installed (nginx -T must be accessible)

Install dependency:

pip install cryptography

🚀 Usage

Check all domains:

python3 nginx_ssl_check.py

Custom thresholds:

python3 nginx_ssl_check.py --warn 30 --crit 7

JSON output:

python3 nginx_ssl_check.py --json

Check specific domains:

python3 nginx_ssl_check.py --domains example.com api.example.com

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