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12. Domains and DNS: GoDaddy, Elastic IP, A/CNAME and Subdomains

12.2 Preparing the Server: Elastic IP and Security Group

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Also in the AWS course: this lesson is the same as 9.4 Before you point a domain: prepare the server in the AWS course, which is the main version of this page.

  1. A working website on EC2, tested with curl -I http://localhost and http://<PUBLIC_IP> (Chapter 8 and 8).

  2. An Elastic IP, so the address never changes after stop/start. Quick steps:

    • EC2 console → Network & Security → Elastic IPs → Allocate Elastic IP address → Allocate.
    • Select it → Actions → Associate Elastic IP address → choose your instance → Associate.
    • Note the address, e.g. 203.0.113.10. SSH now uses this IP too.

    (Charges, the default limit of 5 per region, moving an EIP to a replacement server and releasing it safely are covered in detail in Chapter 12.) 3. Security group: inbound HTTP 80 and HTTPS 443 from 0.0.0.0/0 (and ::/0 for IPv6).

Never point DNS to the auto-assigned public IP

It changes on every stop/start. Your domain would then point to an IP that may soon belong to someone else's instance. Always use an Elastic IP (or a load balancer).

Elastic IP charges

Public IPv4 addresses, including Elastic IPs, are charged by AWS. Release Elastic IPs you no longer need (Disassociate, then Release). Check the AWS pricing page for current details – the UI and pricing may change.

Ravindra Bagale's Tip

You pointed the domain at the auto-assigned public IP and then stopped and started the instance – now the domain may point at someone else's server! Many students have made this mistake. First the Elastic IP, then DNS – never break this order.

Practice task

Allocate an Elastic IP, associate it with your web server, and SSH to the server using the new address.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.