AWS - SSH protocol

What is SSH?

SSH = Secure Shell
It is a network protocol that allows you to securely connect to and manage remote servers over an encrypted channel.

• Works on port 22 (by default).

• Provides authentication (usually via username + password or SSH keys).

• Encrypts all traffic (unlike old protocols like Telnet or FTP which send data in plain text).

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What You Can Do With SSH

1. Remote login → Securely access and control Linux/Unix servers.

2. File transfers → Using scp or sftp (built on SSH).

3. Tunneling/Port forwarding → Securely forward traffic (e.g., database connections).

4. Automation → Used in scripts, CI/CD pipelines for remote execution.

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How SSH Works

1. Client → Server: You run ssh user@server-ip.

2. Handshake: The server and client exchange keys to set up encryption.

3. Authentication:

   • Password-based OR

   • Key-based (preferred) → You use an SSH key pair:

     • Private key (kept safe on your local machine).

     • Public key (stored on the server in ~/.ssh/authorized_keys).

4. Secure Session: You now have a secure shell to run commands remotely.

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SSH in AWS

• When you launch an EC2 instance, you usually connect via SSH.

• AWS gives you a key pair (.pem file) when creating the instance.

• Example command:

  ssh -i my-key.pem ec2-user@ec2-54-123-45-67.compute-1.amazonaws.com
  

• Without SSH, you wouldn’t be able to log in securely to manage EC2 Linux instances.