nginx proxy_pass URL DNS解析失效问题解决

resolver 10.0.0.1;

upstream dynamic {
    zone upstream_dynamic 64k;

    server backend1.example.com      weight=5;
    server backend2.example.com:8080 fail_timeout=5s slow_start=30s;
    server 192.0.2.1                 max_fails=3;
    server backend3.example.com      resolve;
    server backend4.example.com      service=http resolve;

    server backup1.example.com:8080  backup;
    server backup2.example.com:8080  backup;
}

server {
    location / {
        proxy_pass http://dynamic;
        health_check;
    }
}

server {
	listen   80;
	server_name  backend.example.com;
    
    location / {
        resolver 10.0.0.1 valid=30s ipv6=off;
        resolver_timeout 10s;
        set $dynamic  "backend1.example.com";
        proxy_pass http://$dynamic;

    }
}