1、nginx可以作为一个反向代理和负载均衡来使用
反向代理：比如防火墙只有一个IP和端口对外开放，但是内网有多个服务需要连接，那么可以用nginx反向代理功能，通过不同路径的url，映射到不同服务器上
负载均衡：在反向代理功能的基础上，提供软负载的功能，因为硬件负载F5、Array价格昂贵

2、CentOS7上nginx-1.16.1配置文件说明

# For more information on configuration, see:
#   * Official English Documentation: http://nginx.org/en/docs/
#   * Official Russian Documentation: http://nginx.org/ru/docs/

#配置的用户
user nginx;
#nginx的进程数
worker_processes auto;
#错误日志路径和级别
error_log /var/log/nginx/error.log;
#进程pid文件位置
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.
#加载动态模块
include /usr/share/nginx/modules/*.conf;

#events语句块
#worker_connections设置最大连接数
events {
    worker_connections 1024;
}

#http语句块，可包含多个server语句块
http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;

    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        listen       80 default_server;
        listen       [::]:80 default_server;
        server_name  _;
        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
        }

        error_page 404 /404.html;
        location = /404.html {
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    }

# Settings for a TLS enabled server.
#
#    server {
#        listen       443 ssl http2 default_server;
#        listen       [::]:443 ssl http2 default_server;
#        server_name  _;
#        root         /usr/share/nginx/html;
#
#        ssl_certificate "/etc/pki/nginx/server.crt";
#        ssl_certificate_key "/etc/pki/nginx/private/server.key";
#        ssl_session_cache shared:SSL:1m;
#        ssl_session_timeout  10m;
#        ssl_ciphers HIGH:!aNULL:!MD5;
#        ssl_prefer_server_ciphers on;
#
#        # Load configuration files for the default server block.
#        include /etc/nginx/default.d/*.conf;
#
#        location / {
#        }
#
#        error_page 404 /404.html;
#        location = /404.html {
#        }
#
#        error_page 500 502 503 504 /50x.html;
#        location = /50x.html {
#        }
#    }

}

3、反向代理设置
在server语句块外增加

upstream proxy_app1 {
        server 192.168.100.1:80;
}

location /app1/ {
        proxy_pass http://proxy_app1/;
        proxy_redirect off;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        client_max_body_size 10m;
        client_body_buffer_size 128k;
        proxy_connect_timeout 300;
        proxy_send_timeout 300;
        proxy_read_timeout 300;
        proxy_buffer_size 4k;
        proxy_buffers 4 32k;
        proxy_busy_buffers_size 64k;
        proxy_temp_file_write_size 64k;
        }

4、负载均衡
1）upstream语句块可以配置服务器集群和负载均衡策略

upstream proxy_app1 {
        server 192.168.100.1:80;
        server 192.168.100.2:80;
        server 192.168.100.3:80;
}

参考资料：
https://docs.nginx.com/nginx/admin-guide/load-balancer/http-load-balancer/
https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/