反向代理与负载均衡概述

在云服务器架构中，Nginx通常扮演两个关键角色：反向代理将客户端请求转发给后端服务，负载均衡将流量分发到多台后端服务器，实现高可用和高并发处理。

反向代理基础配置

server {
    listen 80;
    server_name example.com;
    
    location / {
        proxy_pass http://127.0.0.1:3000;
        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;
    }
    
    location /static/ {
        alias /var/www/static/;
        expires 30d;
        add_header Cache-Control "public, immutable";
    }
}

负载均衡配置

轮询（Round Robin）— 默认算法

upstream backend {
    server 10.0.0.1:3000;
    server 10.0.0.2:3000;
    server 10.0.0.3:3000;
}

加权轮询

upstream backend {
    server 10.0.0.1:3000 weight=3;
    server 10.0.0.2:3000 weight=2;
    server 10.0.0.3:3000 weight=1;
}

IP哈希（会话保持）

upstream backend {
    ip_hash;
    server 10.0.0.1:3000;
    server 10.0.0.2:3000;
}

最少连接

upstream backend {
    least_conn;
    server 10.0.0.1:3000;
    server 10.0.0.2:3000;
}

健康检查与故障转移

upstream backend {
    server 10.0.0.1:3000 max_fails=3 fail_timeout=30s;
    server 10.0.0.2:3000 max_fails=3 fail_timeout=30s;
    server 10.0.0.3:3000 backup;
}

HTTPS 与 SSL 配置

server {
    listen 443 ssl http2;
    server_name example.com;
    
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_prefer_server_ciphers on;
    ssl_session_cache shared:SSL:10m;
    
    add_header Strict-Transport-Security "max-age=63072000" always;
    
    location / {
        proxy_pass http://backend;
    }
}

# HTTP重定向到HTTPS
server {
    listen 80;
    server_name example.com;
    return 301 https://$host$request_uri;
}

Gzip 压缩与缓存

gzip on;
gzip_vary on;
gzip_min_length 1024;
gzip_types text/plain text/css application/json application/javascript text/xml;

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=api_cache:10m;

location /api/ {
    proxy_cache api_cache;
    proxy_cache_valid 200 5m;
    add_header X-Cache-Status $upstream_cache_status;
}

高可用：Keepalived + Nginx

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    virtual_ipaddress {
        10.0.0.100
    }
}

总结

Nginx作为反向代理和负载均衡器，是构建高性能Web架构的核心组件。合理配置负载均衡算法、SSL加密、缓存策略和高可用方案，可以将系统的并发处理能力从单机数千提升到数万甚至更高。