reverse proxy through the configuration file, add the following location, to nginx.conf and change localhost to the desired ip.

server {
    location /tomcat1 {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8081;
    }
    location /tomcat2 {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8082;
    }
    location /tomcat3 {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8083;
    }
}

/ back up the default configuration file of nginx and change it.
server {
-sharp this is the port 80 you want to proxy to
listen 80;
-sharp this is the domain name
server_name http://localhost;

root html;

access_log logs/nginx.access.log main;

-sharp then here are several tomcat

-sharp default requests
location / {
index index.php index.html index.htm;
}
location / tomcat1 {

        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8081;
    }
    location /tomcat2 {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8082;
    }
    location /tomcat3 {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://localhost:8083;
    }
    -sharp
}

Why the result of my visit is 404; it is possible to access tomcat directly