Connecting to EC2 instances in AWS - Step-by-Step Execution

Process Flow - Connecting to EC2 instances

Start: User wants to connect

↓

Check: EC2 instance running?

No→Start instance

Yes↓

Obtain instance public IP

↓

Use SSH client with key and IP

↓

Authenticate connection

↓

Access EC2 instance shell

↓

End

This flow shows the steps to connect to an EC2 instance: ensure it is running, get its IP, use SSH with the key, authenticate, and access the shell.

Execution Sample

AWS

ssh -i MyKey.pem ec2-user@54.123.45.67
# Connects to EC2 instance using SSH and private key

This command connects your computer to the EC2 instance at IP 54.123.45.67 using the private key file MyKey.pem.

Process Table

Step	Action	Check/Command	Result/Output
1	Check if EC2 instance is running	aws ec2 describe-instances	Instance state: running
2	Get public IP address	aws ec2 describe-instances --query 'Reservations[].Instances[].PublicIpAddress' --output text	54.123.45.67
3	Run SSH command	ssh -i MyKey.pem ec2-user@54.123.45.67	Connecting...
4	Authenticate using private key	SSH client uses MyKey.pem	Authentication successful
5	Access EC2 shell	Shell prompt appears	User logged into EC2 instance
6	Exit connection	exit command	Connection closed

💡 Connection ends when user types 'exit' or disconnects

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
EC2 Instance State	unknown	running	running	running	running
Public IP	none	54.123.45.67	54.123.45.67	54.123.45.67	54.123.45.67
SSH Connection	not started	not started	connecting	connected	closed

Key Moments - 3 Insights

Why do I need the private key file (MyKey.pem) to connect?

The private key file is used to securely authenticate you to the EC2 instance. Without it, the SSH connection will fail (see Step 4 in execution_table).

What if the EC2 instance is not running?

You must start the instance before connecting. The flow checks instance state first (Step 1). If not running, start it to get a public IP and accept connections.

Why do I use the public IP address in the SSH command?

The public IP is the address your computer uses to reach the EC2 instance over the internet (Step 2). Without it, SSH cannot find the instance.

Visual Quiz - 3 Questions

Look at the execution_table, what is the EC2 instance state after Step 2?

A stopped

B pending

C running

D terminated

💡 Hint

Check the 'Result/Output' column for Step 1 and Step 2 in execution_table.

At which step does the SSH client authenticate using the private key?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look for the 'Authenticate using private key' action in execution_table.

If the EC2 instance was stopped initially, which step would change?

A All of the above

B Step 3 would fail to connect

C Step 1 would show 'Instance state: stopped' and require starting instance

D Step 5 would not show shell prompt

💡 Hint

Consider what happens if the instance is not running before connection attempts.

Concept Snapshot

Connecting to EC2 instances:
1. Ensure instance is running.
2. Get its public IP address.
3. Use SSH with your private key file.
4. Authenticate and access the shell.
5. Exit when done.

Full Transcript

To connect to an EC2 instance, first check if it is running. If not, start it. Then find its public IP address. Use an SSH client with your private key file to connect to that IP. The SSH client authenticates you using the key. Once connected, you get a shell prompt on the EC2 instance. When finished, type 'exit' to close the connection.

Practice

1. What is the primary method to securely connect to an AWS EC2 Linux instance?

easy

A. Using FTP with username and password

B. Using HTTP protocol

C. Using SSH with a private key file

D. Using RDP without any credentials

Solution

1. Step 1: Understand connection protocols for EC2 Linux

   Linux EC2 instances use SSH (Secure Shell) for secure remote access.

2. Step 2: Identify the authentication method

   SSH requires a private key file (.pem) to authenticate securely without passwords.

3. Final Answer:

   Using SSH with a private key file -> Option C

4. Quick Check:

   SSH + private key = secure EC2 Linux access [OK]

Hint: SSH with private key is standard for Linux EC2 [OK]

Common Mistakes:

• Trying to use HTTP or FTP for EC2 Linux connection
• Using RDP which is for Windows instances
• Connecting without a private key

2. Which command correctly connects to an EC2 instance with IP 203.0.113.25 using the private key file mykey.pem and default username ec2-user?

easy

A. ssh -key mykey.pem ec2-user@203.0.113.25

B. ssh -i mykey.pem ec2-user@203.0.113.25

C. ssh ec2-user@203.0.113.25 -i mykey.pem

D. ssh -pem mykey.pem ec2-user@203.0.113.25

Solution

1. Step 1: Recall SSH command syntax for private key

   The correct syntax is ssh -i <keyfile> <user>@<ip>.

2. Step 2: Match the command with the syntax

   ssh -i mykey.pem ec2-user@203.0.113.25 matches the correct order and flags exactly.

3. Final Answer:

   ssh -i mykey.pem ec2-user@203.0.113.25 -> Option B

4. Quick Check:

   ssh -i keyfile user@ip = correct syntax [OK]

Hint: Use -i before key file in ssh command [OK]

Common Mistakes:

• Placing -i after user@ip
• Using -key or -pem flags which don't exist
• Omitting the -i flag

3. Given the command ssh -i mykey.pem ubuntu@198.51.100.10, what will happen if the private key file mykey.pem has permissions set to 777?

medium

A. Connection will fail due to insecure key file permissions

B. Connection will succeed without warnings

C. SSH will prompt for a password instead

D. The instance will reject the username 'ubuntu' automatically

Solution

1. Step 1: Understand SSH key file permission requirements

   SSH requires private key files to have strict permissions (usually 400 or 600) to prevent unauthorized access.

2. Step 2: Effect of 777 permissions on SSH connection

   Permissions 777 are too open, so SSH refuses to use the key and fails the connection.

3. Final Answer:

   Connection will fail due to insecure key file permissions -> Option A

4. Quick Check:

   Too open key permissions = connection failure [OK]

Hint: Private key must have strict permissions (chmod 400) [OK]

Common Mistakes:

• Assuming connection works with any key permissions
• Thinking SSH will ask for password if key is insecure
• Believing username causes rejection here

4. You try to connect to your EC2 instance but get a timeout error. Which of the following is the MOST likely cause?

medium

A. Your private key file is missing

B. The instance is running Windows OS

C. You used the wrong username for the instance

D. Your security group does not allow inbound SSH (port 22) traffic

Solution

1. Step 1: Analyze timeout error causes

   Timeout usually means network traffic is blocked or unreachable, not authentication issues.

2. Step 2: Check security group rules

   If inbound SSH (port 22) is not allowed, connection attempts will time out.

3. Final Answer:

   Your security group does not allow inbound SSH (port 22) traffic -> Option D

4. Quick Check:

   Timeout = blocked port 22 in security group [OK]

Hint: Check security group allows port 22 inbound [OK]

Common Mistakes:

• Confusing timeout with wrong username errors
• Assuming missing key causes timeout instead of auth failure
• Thinking OS type causes timeout

5. You have an EC2 instance running Amazon Linux and another running Ubuntu. Which usernames should you use to connect via SSH respectively?

hard

A. ec2-user for Amazon Linux, ubuntu for Ubuntu

B. root for Amazon Linux, admin for Ubuntu

C. admin for Amazon Linux, ec2-user for Ubuntu

D. ubuntu for Amazon Linux, ec2-user for Ubuntu

Solution

1. Step 1: Identify default SSH usernames per OS

   Amazon Linux uses ec2-user and Ubuntu uses ubuntu as default SSH usernames.

2. Step 2: Match usernames to instances

   Use ec2-user for Amazon Linux and ubuntu for Ubuntu instances.

3. Final Answer:

   ec2-user for Amazon Linux, ubuntu for Ubuntu -> Option A

4. Quick Check:

   Amazon Linux = ec2-user, Ubuntu = ubuntu [OK]

Hint: Match username to OS: ec2-user for Amazon Linux [OK]

Common Mistakes:

• Using root or admin instead of default usernames
• Mixing usernames between OS types
• Assuming username is always 'admin'