引言

反向代理和负载均衡是Nginx的核心功能。本文详细讲解其配置和应用。

一、反向代理

1.1 基本配置

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server {
    listen 80;
    server_name api.example.com;

    location / {
        proxy_pass http://backend_server;
        
        # 请求头设置
        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;
        
        # 超时设置
        proxy_connect_timeout 60s;
        proxy_send_timeout 60s;
        proxy_read_timeout 60s;
        
        # 缓冲设置
        proxy_buffering on;
        proxy_buffer_size 4k;
        proxy_buffers 8 4k;
    }
}

1.2 WebSocket代理

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location /ws {
    proxy_pass http://websocket_backend;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_read_timeout 86400;
}

1.3 动静分离

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server {
    listen 80;
    server_name example.com;

    # 静态资源
    location ~* \.(jpg|jpeg|png|gif|css|js)$ {
        root /var/www/static;
        expires 30d;
        add_header Cache-Control "public, immutable";
    }

    # 动态请求
    location / {
        proxy_pass http://backend;
    }
}

二、负载均衡算法

2.1 轮询（默认）

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upstream backend {
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
    server 192.168.1.12:8080;
}

2.2 加权轮询

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upstream backend {
    server 192.168.1.10:8080 weight=5;
    server 192.168.1.11:8080 weight=3;
    server 192.168.1.12:8080 weight=2;
}

2.3 IP哈希

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upstream backend {
    ip_hash;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

2.4 最少连接

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upstream backend {
    least_conn;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

2.5 一致性哈希

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upstream backend {
    hash $request_uri consistent;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

三、健康检查

3.1 被动健康检查

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upstream backend {
    server 192.168.1.10:8080 max_fails=3 fail_timeout=30s;
    server 192.168.1.11:8080 max_fails=3 fail_timeout=30s;
}

3.2 主动健康检查（商业版）

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upstream backend {
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
    
    health_check interval=5s fails=3 passes=2;
}

四、会话保持

4.1 IP哈希

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upstream backend {
    ip_hash;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}
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upstream backend {
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
    sticky cookie srv_id expires=1h domain=.example.com path=/;
}

五、高可用架构

5.1 Keepalived + Nginx

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# 安装Keepalived
yum install keepalived

# /etc/keepalived/keepalived.conf
vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.1.100
    }
}

5.2 完整架构示例

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# 主Nginx配置
upstream backend_api {
    least_conn;
    server 192.168.1.10:8080 max_fails=2 fail_timeout=10s;
    server 192.168.1.11:8080 max_fails=2 fail_timeout=10s;
    server 192.168.1.12:8080 max_fails=2 fail_timeout=10s backup;
}

upstream backend_web {
    ip_hash;
    server 192.168.1.20:80;
    server 192.168.1.21:80;
}

server {
    listen 80;
    server_name example.com;

    # API请求
    location /api {
        proxy_pass http://backend_api;
        proxy_next_upstream error timeout http_500 http_502 http_503;
        
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

    # Web请求
    location / {
        proxy_pass http://backend_web;
        proxy_set_header Host $host;
    }
}

六、监控与调试

6.1 状态监控

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location /nginx_status {
    stub_status on;
    access_log off;
    allow 127.0.0.1;
    deny all;
}

6.2 upstream状态

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location /upstream_status {
    upstream_status;
    access_log off;
}

七、常见问题

7.1 502 Bad Gateway

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原因：
1. 后端服务未启动
2. 网络不通
3. 超时时间过短

解决：
- 检查后端服务状态
- 检查防火墙
- 增加超时时间

7.2 负载不均衡

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# 可能原因：
# 1. 使用ip_hash但客户端IP相同
# 2. 长连接导致连接不释放

# 解决：
upstream backend {
    least_conn;  # 使用最少连接算法
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
    
    keepalive 32;  # 启用长连接池
}

总结

Nginx负载均衡核心：

  1. 算法选择：根据场景选择合适的算法
  2. 健康检查：及时发现故障节点
  3. 会话保持：保证用户请求到同一后端
  4. 高可用：Keepalived实现故障转移
  5. 监控调试：实时监控系统状态

参考资料