# 1. 定義後端伺服器群組 (Upstream)
upstream backend_cluster {
    # 策略 A: Round Robin 輪詢 (預設)
    # 策略 B: ip_hash; (同一 IP 鎖定同一台伺服器，解決 Session 問題)
    # 策略 C: least_conn; (優先指派給當前連線數最少的伺服器)

    server 127.0.0.1:9090 max_fails=3 fail_timeout=10s;
    server 127.0.0.1:9091 max_fails=3 fail_timeout=10s;
    server 127.0.0.1:9092 backup; # 備援節點：前兩台都掛掉時才接手
}

server {
    listen 80;
    server_name example.com;
    # 將所有 HTTP 80 流量強制轉導至 HTTPS 443
    return 301 https://$host$request_uri;
}

server {
    listen 443 ssl http2;
    server_name example.com;

    # Certbot 自動寫入的 SSL 憑證路徑
    ssl_certificate /etc/letsencrypt/live/yourdomain.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/yourdomain.com/privkey.pem;

    location / {
        # 將流量代理轉發至 upstream 群組
        proxy_pass http://backend_cluster;

        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 $scheme;
    }
}