Nginx Subdomain accessible on subdomain its not configured for - nginx

Question

I have my staging config setup like so:
server {
listen 80;
server_name staging.domain.com;
root /var/www/staging/public;
and my production config setup like this:
server {
listen 80;
server_name www.domain.com;
root /var/www/production/public;
With no other redirects or anything.
The issue is that even if I disable the production config I can still access the staging server at www.domain.com.
Why is it not being restricted to its configured subdomain?

Answer 1

I've answered a similar question like this before
Let me start with a small explanation on how nginx matches the hosts, quoting from how nginx processes a request
In this configuration nginx tests only the request’s header field
“Host” to determine which server the request should be routed to. If
its value does not match any server name, or the request does not
contain this header field at all, then nginx will route the request to
the default server for this port.
When you disable the main server you only have 1 left, so nginx passes the request to it, if you want to avoid that you need to add a main server to block all unconfigured domains
server {
listen 80 default_server;
return 403;
}
Then run
sudo service nginx reload
Then you're set