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Networking and Access in Cloud Computing

Learn about Networking and Access in this comprehensive Cloud Computing tutorial. The fundamentals of instance addressing and authentication.

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1The Changing Public IP

A common beginner mistake is hardcoding an EC2 instance's Public IP into an application, only to have the app break when the instance is stopped and started. Always use DNS names or Elastic IPs for production workloads.

2Cryptography over Passwords

AWS strongly discourages password-based logins for Linux. Asymmetric cryptography (Key Pairs) is mathematically much harder to brute-force than any password. Keep your .pem file safe; if you lose it, you might lose access to the instance.

3Step-by-Step Breakdown

IP Addresses. Every EC2 instance gets an IP address to communicate. There are two main types: Public and Private.

Private IPs. A Private IP is assigned when the instance launches and stays with it until termination. It is used for communication within the VPC.

Public IPs. A Public IP allows the instance to be reached from the internet. However, if you stop and start the instance, the Public IP changes!

Elastic IPs (EIP). If you need a permanent Public IP that survives restarts, you allocate an Elastic IP and associate it with your instance.

SSH. Secure Shell (SSH) is the protocol used to securely log into Linux instances over the network.

IP Check. Which type of IP address changes when you stop and start an EC2 instance?

→Private IP
→Elastic IP
→Default Public IP

Key Pairs. AWS uses public-key cryptography. AWS stores the Public Key on the instance, and you keep the Private Key (.pem or .ppk file).

Key Permissions. On Linux/Mac, SSH requires your private key file to have strict permissions, otherwise it will reject the connection.

EC2 Instance Connect. If you lose your key or don't want to manage them, AWS offers EC2 Instance Connect to SSH directly from the browser.

Completion. You can now connect to your servers securely.

Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Using an instance's public IP for internal, instance-to-instance communication

// Wrong: server A calls server B's public IP for internal traffic
// Correct: use the private IP within the same VPC
curl http://10.0.1.15:8080/api

The Solution //

Traffic between two instances in the same VPC routed via public IPs leaves the private network path and can incur unnecessary data transfer charges and latency. Use the private IP (or private DNS name) for any traffic that stays within the VPC.

The Error //

Relying on an instance's default public IP surviving a stop/start cycle

aws ec2 allocate-address --domain vpc
aws ec2 associate-address --instance-id i-1234567890abcdef0 --allocation-id eipalloc-12345678

The Solution //

A standard auto-assigned public IP is released when an instance is stopped and a new one is assigned on start — any hardcoded reference to the old IP breaks. If a stable public IP is required, allocate an Elastic IP and associate it explicitly.