How to ssh from one ec2 instance to another?

Source:
https://superuser.com/questions/1135766/how-to-ssh-from-one-ec2-instance-to-another
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/security-group-rules-reference.html

Rules to connect to instances from an instance with the same security group

To allow instances that are associated with the same security group to communicate with each other, you must explicitly add rules for this.

The following table describes the inbound rule for a security group that enables associated instances to communicate with each other. The rule allows all types of traffic.

Protocol type	Protocol number	Ports	Source IP
-1 (All)	-1 (All)	-1 (All)	The ID of the security group

Method 1 - use the same keys on the servers:

Convert the keys to openssh format and upload the private keys to the servers. When you ssh to the destination host, specify the private key file:

ssh -i mykey.pem private.ip.of.other.server

---

Method 2 - Create new keys

On each server run:

ssh-keygen

Hit enter enter enter. You'll have two files:

.ssh/id_rsa
.ssh/id_rsa.pub

On Server A, cat and copy to clipboard the public key:

cat ~/.ssh/id_rsa.pub
[select and copy to your clipboard]

ssh into Server B, and append the contents of that to the it's authorized_keys file:

cat >> ~/.ssh/authorized_keys
[paste your clipboard contents]
[ctrl+d to exit]

Now ssh from server A:

ssh -i ~/.ssh/id_rsa private.ip.of.other.server