nginx: configuration file /etc/nginx/nginx.conf test failed (host not found in upstream)
All you need is to put resolver that can resolve such domain name:
resolver 8.8.8.8 valid=300s;resolver_timeout 10s;
Google DNS (8.8.8.8) can resolve it, but it resolves to internal address belongs to network class C.
$ dig @8.8.8.8 www.class.com.192.168.33.10.xip.io;; ANSWER SECTION:www.class.com.192.168.33.10.xip.io. 299 IN A 192.168.33.10
Your problem is coming from this line:
proxy_pass http://www.class.com.192.168.33.10.xip.io:8055;
Most likely the server is having difficulty resolving that DNS name. You may also want to look at https://serverfault.com/questions/341810/nginx-failing-to-resolve-upstream-names-on-reload-even-if-they-do-resolve-by-the