It is pretty obvious that hostnames can replace IP addresses. Pretty much any software accepting an IP address will also accept a hostname as an argument. Last week, I wrote about scans for the cloud metadata service listening at 169.254.169.254. These scans attempted to exploit Server Side Request Forgery (SSRF) vulnerability. One way to prevent these types of exploits is to filter requests that contain the string "169.254.169.254" or to add this IP to a blocklist of URLs that should not be accessed.