Key pairs for SSH access in AWS - Commands & Configuration

Introduction

When you want to securely connect to a remote server, you need a way to prove who you are without using a password. Key pairs help by using a secret key on your computer and a matching public key on the server to allow safe access.

When you launch a new virtual server in the cloud and want to connect to it securely.

When you want to avoid using passwords for logging into your cloud servers.

When you need to share access to a server without sharing your private key.

When you want to automate secure connections to your cloud servers.

When you want to manage access keys centrally in your cloud environment.

Commands

This command creates a new SSH key pair named 'my-ssh-key' in AWS and saves the private key to a file called 'my-ssh-key.pem' on your computer. The private key is needed to connect to your server.

Terminal

aws ec2 create-key-pair --key-name my-ssh-key --query 'KeyMaterial' --output text > my-ssh-key.pem

Expected Output

No output (command runs silently)

→

--key-name - Sets the name of the key pair in AWS.

→

--query - Extracts only the private key material from the output.

→

--output - Formats the output as plain text for saving.

This command changes the file permissions of your private key so that only you can read it. This is important for security and SSH will refuse to use the key if permissions are too open.

Terminal

chmod 400 my-ssh-key.pem

Expected Output

No output (command runs silently)

This command checks that your key pair named 'my-ssh-key' exists in AWS. It helps confirm that the key pair was created successfully.

Terminal

aws ec2 describe-key-pairs --key-names my-ssh-key

Expected Output

{

    "KeyPairs": [

        {

            "KeyName": "my-ssh-key",

            "KeyPairId": "key-0abcd1234efgh5678",

            "KeyFingerprint": "1a:2b:3c:4d:5e:6f:7g:8h:9i:0j:kl:mn:op:qr:st:uv"

        }

    ]

}

→

--key-names - Specifies the name of the key pair to describe.

This command uses your private key file to securely connect to your AWS server as the user 'ec2-user'. Replace the hostname with your server's public DNS name.

Terminal

ssh -i my-ssh-key.pem [e-mail]

Expected Output

Last login: Tue Jun 6 12:34:56 2024 from 203.0.113.25

[ec2-user@ip-172-31-0-1 ~]$

→

-i - Specifies the private key file to use for authentication.

Key Concept

If you remember nothing else from this pattern, remember: the private key stays on your computer and the public key is stored on the server to allow secure, password-free login.

Common Mistakes

Not setting the private key file permissions to 400.

SSH refuses to use private keys that are accessible by others for security reasons.

Always run 'chmod 400 my-ssh-key.pem' to restrict access to your private key.

Trying to connect with the wrong username or server address.

The SSH connection will fail if the username or server hostname is incorrect.

Use the correct username (like 'ec2-user' for Amazon Linux) and the server's public DNS or IP address.

Sharing the private key file with others.

Anyone with your private key can access your servers, risking security breaches.

Keep your private key secret and share only the public key if needed.

Summary

Create a key pair in AWS and save the private key file locally.

Set strict permissions on the private key file to keep it secure.

Verify the key pair exists in AWS before using it.

Use the private key file to SSH into your cloud server securely.

Practice

1. What is the main purpose of a key pair in AWS for SSH access?

easy

A. To store server data securely

B. To securely connect to a server without using a password

C. To create a backup of the server

D. To monitor server performance

Solution

1. Step 1: Understand SSH access

   SSH uses keys to allow secure login without passwords.

2. Step 2: Role of key pairs in AWS

   A key pair provides a private key for the user and a public key for the server to verify identity.

3. Final Answer:

   To securely connect to a server without using a password -> Option B

4. Quick Check:

   Key pairs enable passwordless secure login [OK]

Hint: Key pairs replace passwords for secure server login [OK]

Common Mistakes:

• Thinking key pairs store server data
• Confusing key pairs with backups
• Assuming key pairs monitor performance

2. Which AWS CLI command correctly creates a new key pair named MyKey and saves the private key to a file?

easy

A. aws ec2 create-key-pair --key-name MyKey --query 'KeyMaterial' --output text > MyKey.pem

B. aws ec2 create-key-pair MyKey > MyKey.pem

C. aws ec2 generate-key-pair --name MyKey > MyKey.pem

D. aws ec2 new-key --key-name MyKey > MyKey.pem

Solution

1. Step 1: Identify correct AWS CLI syntax

   The correct command uses create-key-pair with --key-name and outputs the private key material.

2. Step 2: Confirm output redirection

   The private key is saved by redirecting the output to a file with > MyKey.pem.

3. Final Answer:

   aws ec2 create-key-pair --key-name MyKey --query 'KeyMaterial' --output text > MyKey.pem -> Option A

4. Quick Check:

   Correct AWS CLI syntax for key pair creation [OK]

Hint: Use create-key-pair with --query 'KeyMaterial' to save private key [OK]

Common Mistakes:

• Using wrong command like generate-key-pair
• Omitting --query to extract key material
• Not redirecting output to save private key

3. You launched an EC2 instance with key pair MyKey. Which command will you use to connect to it if the instance's public IP is 54.12.34.56 and your private key file is MyKey.pem?

medium

A. ssh ec2-user@54.12.34.56 -i MyKey.pem

B. ssh -key MyKey.pem ec2-user@54.12.34.56

C. ssh -p MyKey.pem ec2-user@54.12.34.56

D. ssh -i MyKey.pem ec2-user@54.12.34.56

Solution

1. Step 1: Understand SSH command syntax for key usage

   The -i option specifies the private key file for authentication.

2. Step 2: Confirm correct order of arguments

   The correct syntax is ssh -i private_key user@host. ssh -i MyKey.pem ec2-user@54.12.34.56 matches this exactly.

3. Final Answer:

   ssh -i MyKey.pem ec2-user@54.12.34.56 -> Option D

4. Quick Check:

   SSH uses -i to specify private key file [OK]

Hint: Use ssh -i private_key user@ip to connect [OK]

Common Mistakes:

• Using -key or -p instead of -i
• Placing -i after user@host
• Omitting the private key option

4. You tried to connect to your EC2 instance using SSH but got a permission denied error. Which of these is the most likely cause?

medium

A. The private key file has incorrect permissions (too open)

B. The instance is stopped

C. The key pair was deleted from AWS

D. The instance has no public IP

Solution

1. Step 1: Check SSH private key file permissions

   SSH requires private key files to have strict permissions (e.g., 400). Too open permissions cause denial.

2. Step 2: Understand other options

   While stopped instances or no public IP prevent connection, the error message differs. Deleted key pairs do not affect existing instances.

3. Final Answer:

   The private key file has incorrect permissions (too open) -> Option A

4. Quick Check:

   Private key file permissions cause SSH denial [OK]

Hint: Set private key file permission to 400 or stricter [OK]

Common Mistakes:

• Ignoring file permission errors
• Assuming instance state causes permission denied
• Confusing deleted key pairs with connection errors

5. You lost your private key file for an EC2 instance launched with key pair OldKey. What is the best way to regain SSH access without stopping the instance?

hard

A. Use the AWS console to download the lost private key again

B. Delete the instance and launch a new one with a new key pair

C. Create a new key pair, then update the instance's authorized keys by connecting through Systems Manager or another user

D. Generate a new private key file with the same key name in AWS

Solution

1. Step 1: Understand private key loss impact

   Private keys cannot be recovered or downloaded again from AWS once lost.

2. Step 2: Regain access without stopping instance

   Use AWS Systems Manager or another user with access to add a new public key from a new key pair to the instance's authorized keys.

3. Final Answer:

   Create a new key pair, then update the instance's authorized keys by connecting through Systems Manager or another user -> Option C

4. Quick Check:

   Lost private key requires new key and authorized keys update [OK]

Hint: Use Systems Manager to add new key without stopping instance [OK]

Common Mistakes:

• Trying to download lost private key again
• Assuming new key pair with same name works
• Deleting instance unnecessarily