A security group acts as a virtual firewall that controls the traffic for one or more instances. You can modify the rules for a security group at any time; the new rules are automatically applied to all instances that are associated with the security group.

We can create a security group with certain rules and apply one security group to multiple servers.
Each account will have default security group created.
By default, security groups allow all outbound traffic.

To create a new security group using the console

Open the Amazon EC2 dashboard
In the left navigation pane, choose Security Groups and Create Security Group.
Specify a name and description for the security group.
You can start adding rules once it is created.E
Each Security group will have description, inbound, outbound and tags information at the bottom which displays necessary information.
- Description – name, id, description and VPC id information will be shown.
- Inbound – What ports are open to connecting to the server
- Outbound – What or how an instance can connect to the other servers
- To update a security group, choose the instance and click on Actions–>Edit Inbound Rules/Edit Outbound Rules.

Troubleshooting the connection issues

To check, whether the port number is connected or not, we can use Telnet.
To connect telnet, we can use the below command

telnet <public_DNS> <port_number>

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