Security groups establish a set of access rules for one or more servers. In practice, they are equivalent to a firewall, that is, they allow certain services to be accessible to the Internet or to only certain pre-configured IPs.
Amazon by default closes all ports and it is necessary to release the ports for your server services.
For example, to allow access to a web server such as Apache or Microsoft IIS, the following ports could be released:
- 80 and 443 – access to the web server
- ICMP – ping do servidor
- 22 – SSH access (Linux only)
- 3389 – Remote Terminal access (Windows only)
- etc…