I expect ms.fbny.org to be an alias of music-school.fbny.org. However when I go to ms.fbny.org, it actually goes to music-school.fbny.org's IP instead of music-school.fbny.org itself. So it is opening another website hosted on the same IP. Is this a normal behavior?
Yes, this is the default behavior. The web server should be configured to serve from the correct document root when the request comes from a specific subdomain.
For example, if you use apache, you should configure virtual hosts appropriately.
Above page contains the below example:
# Ensure that Apache listens on port 80 Listen 80 <VirtualHost *:80> DocumentRoot "/www/example1" ServerName www.example.com # Other directives here </VirtualHost> <VirtualHost *:80> DocumentRoot "/www/example2" ServerName www.example.org # Other directives here </VirtualHost>
www.example.org will be served from the folder
/www/example2 and those from
www.example.com will be served from
/www/example1. Moreover, apache considers the first entry to be the default when there is no match for a server name.
(In case you use apache) your new subdomain (for which you had created a CNAME) may not be having a matching entry and hence default document root of the main domain is being used.