Tomcat report error: multiple tomcat deployments on one server report error "The character [_] is always invalid in the domain name."

Experimental environment: Two tomcats are used for load balancing on nginx, and the load code is as follows:

    upstream tomcat_local {
    
    
     server 192.168.8.186:8080 weight=1;
     server 192.168.8.186:8081 weight=2;
   }
server {
    
    
        listen       80;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;
        location / {
    
    
            root html;
            proxy_pass http://tomcat_local;
        #    proxy_set_header Host $host:$server_port;
        #    proxy_set_header X-Real-IP $remote_addr;
        #    proxy_set_header REMOTE-HOST $remote_addr;
        #    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }

Access http://192.168.8.186/will report an error! ! !
Error content:


Error reason:tomcat_local There is an underscore in the domain name _, and if the Host of proxy_set_header is not set, the value corresponding to proxy_pass will be used directly, which is tomcat_local. But the underscore is illegal for the domain name, so an error 400 error request will be reported.
Solution:
① Method 1: Remove the underscore, for example, write the domain name as tomcatlocal
② Method 2: Modify the reverse proxy configuration as follows:

        location / {
    
    
            root html;
            proxy_pass http://tomcat_local;
            proxy_set_header Host $host:$server_port;    # nginx服务器的主机名和端口号，不使用tomcat_local
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header REMOTE-HOST $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }