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Chapter 13: Amazon EBS (Elastic Block Store)

Common Mistakes I See Students Make

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Friends, I see these EBS mistakes in every batch – the wrong AZ, mkfs on a disk that has data, the device name in fstab. Read them once – lost data doesn't come back.

  • Creating the volume in a different AZ from the instance — it simply won't appear in the attach list.
  • Running mkfs on a volume that already has data (e.g. restored from a snapshot) and wiping it.
  • Using /dev/sdf or /dev/nvme1n1 in fstab instead of the UUID.
  • Forgetting nofail and the instance hangs at boot when the volume is missing.
  • Running resize2fs on an XFS filesystem (use xfs_growfs) or giving xfs_growfs a device instead of the mount point.
  • Forgetting the space in growpart /dev/nvme0n1 1.
  • Detaching without unmounting, risking data corruption.
  • Leaving unattached volumes and old snapshots that keep costing money.

Extended notes for this AWS lesson

Why students get stuck here

AWS pages look simple until three things collide: the service setting, the VPC/security group, and the app configuration. The expansions below separate those layers with real stacks and sample commands.

Always check three layersAWS servicesettingNetworkSG / NACL / DNSApp configendpoint / driver
Most "it does not connect" tickets miss one of these three.

The same pattern in app stacks

Whether the data store is RDS MySQL, PostgreSQL, or another engine, apps read an endpoint + user + password from the environment.

Java / Spring Boot

spring.datasource.url=jdbc:mysql://ENDPOINT:3306/db with password from Secrets Manager / env.

Python / Django / Flask

HOST from env; never commit settings with real hosts.

Node.js

mysql2/pg clients with process.env.DB_HOST.

.NET

ConnectionStrings via env or Parameter Store.

PHP / Laravel

DB_HOST in .env, not in Git.

Go

database/sql with env-based DSN.

Indian company (sample)

Suppose we are a junior cloud engineer at Swiggy or Razorpay-style infrastructure. A new microservice cannot reach RDS. You check: 1) SG on RDS allows the app SG on 3306/5432. 2) App is in a private subnet with a route to the DB subnet. 3) The secret in Secrets Manager matches the rotated password. 4) You connect with the mysql/psql client from the app host before blaming the ORM.

Global practice

AWS Well-Architected Security and Reliability pillars: least-privilege SG, Multi-AZ for production relational DBs, automated backups, no public DB reachability.

Everyday analogy

A warehouse (RDS) should not open onto the street. Delivery bikes (app servers) enter through a staff gate (security group) with a badge (password/IAM auth).

Engines and ports

MySQL / MariaDB on RDS

Port 3306. Users and grants like self-managed MySQL.

PostgreSQL on RDS

Port 5432. Prefer scram auth.

SQL Server on RDS

Port 1433. Common with .NET shops.

Amazon Aurora

MySQL or PostgreSQL compatible; learn the endpoint types (cluster vs reader).

Load balancers in one breath

ALB is for HTTP/HTTPS apps (Spring, Node, Django, .NET). NLB is for extreme performance/TCP. GLB is for virtual appliances. Classic LB is legacy—prefer ALB/NLB for new work. Always put TLS on the balancer with ACM when you can.

Common EC2 and Linux mistakes (expanded)

  1. Losing the SSH key → use SSM Session Manager next time.
  2. Editing on the server without backups → keep AMI + user-data scripts.
  3. Opening 0.0.0.0/0 on SSH → restrict to your IP or VPN.
  4. Forgetting Elastic IP / DNS when testing restarts.
  5. Growing EBS without extending the Linux filesystem (growpart + resize2fs/xfs_growfs).

Common mistakes

  • Publicly accessible RDS "for a quick test" left open.
  • Mixing Classic LB advice with ALB listener rules.
  • Hard-coding IPs instead of DNS names for RDS endpoints.
  • Taking snapshots but never testing restore.

Worksheet

  1. Draw your VPC boxes: public subnet, private subnet, RDS subnet.
  2. Write the SG rules in a table.
  3. From the app host, run a one-line DB client connect.
  4. Take a snapshot and write the restore steps without looking.

Recap

  • Service + network + app config.
  • Private databases.
  • Prefer ALB + ACM for web apps.
  • Practise restore, not only backup.