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Chapter 45: Terraform 3-Tier Architecture in a Single Availability Zone

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Chala mitrano, aata khari architecture. Web, app aani database — teen layer, ekach zone madhe. Web public subnet madhe, app private madhe, database DB subnet madhe. Security group chain neet samjun ghya, karan pudhcha multi-AZ chapter yavarach ubha aahe.

What you will learn in this chapter

  • Design a VPC with public, private app and DB subnets in one zone
  • Route private traffic through a NAT gateway
  • Chain security groups web to app to database
  • Pass the app private IP into nginx with Terraform
  • Create a DB subnet group and a single-AZ RDS
  • Apply, test and destroy the stack

Concepts in this chapter

  1. 45.1The single-AZ 3-tier design, file layout and network
  2. 45.2Security groups for web, app and database tiers
  3. 45.3Web tier and app tier EC2 servers
  4. 45.4Database tier: DB subnet group and single-AZ RDS
  5. 45.5Apply, test and destroy the single-AZ 3-tier stack

The chapter recap is at the end of the last concept page.

Practice Tasks

About this scenario

Suppose we are on the DevOps team at Maruti Suzuki, the automobile company, working from Gurugram. Deepak Chauhan leads the team, and we look after the service booking portal. Costs are counted in INR. In the tasks below we do real DevOps jobs on this project using what this lesson teaches. Maruti Suzuki is a real company, but this project, the people, servers, IP addresses and numbers are made up for practice.

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Easy S3 bucket resource

Why: Buckets in code are reviewed and never forgotten.

What to do: Write a resource aws_s3_bucket named logs with bucket = "maruti-logs" and tags { Team = "devops" }.

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Easy Output a value

Why: Outputs hand values to scripts and other modules.

What to do: Write output "web_ip" with value = aws_instance.web.public_ip.

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Easy Provider block

Why: The provider tells Terraform which cloud and region to talk to.

What to do: Write a provider "aws" block with region = "ap-south-1".

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Easy Connect to an EC2 server

Why: SSH with a key file is the standard way to log in to a Linux EC2 instance.

What to do: Log in to the server 13.31.20.5 as ec2-user using the key maruti-key.pem.

How:
  1. Find the Linux command that does this job.
  2. Add the options (like -r or -h) the task needs.
  3. Add the file names, folders or users in the right order.
  4. Click Check answer.

Easy Name the practice

Why: IaC is the base of repeatable cloud setups.

What to do: Maruti Suzuki describes its servers, networks and databases in text files kept in Git and creates them with a tool. What is this called (three-letter short form)?

How:
  1. Write down the facts or numbers the task gives you.
  2. Work it out step by step.
  3. Type only the final answer (one word or number) in the box.
  4. Click Check answer.

Medium EC2 instance using a variable

Why: Referencing var.* avoids hard-coding sizes.

What to do: Write resource aws_instance "web" with ami = "ami-0abcdef1234567890", instance_type = var.instance_type and tags Name = "service-booking".

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Medium Pin the provider version

Why: Pinning stops a new provider release from breaking your plan.

What to do: Write a terraform block with required_providers aws = { source = "hashicorp/aws", version = "~> 5.0" }.

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Medium Apply the saved plan

Why: No surprise changes: only the reviewed plan runs.

What to do: Apply the saved plan file maruti.tfplan.

How:
  1. Read the task and pick the tool it needs (git, docker, kubectl, terraform, ansible...).
  2. Write the tool name, then the sub-command (the action word).
  3. Add the flags the task needs, each followed by its value.
  4. Add names, files or paths at the end, then click Check answer.

Hard Security group for HTTPS

Why: Opening only 443 keeps the attack surface small.

What to do: Write resource aws_security_group "web" with name = "web-sg" and one ingress block: from_port = 443, to_port = 443, protocol = "tcp", cidr_blocks = ["0.0.0.0/0"].

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Hard Create several copies with count

Why: count builds N identical resources from one block.

What to do: Write resource aws_instance "worker" with count = 3, ami = "ami-0abcdef1234567890", instance_type = "t3.small" and tags Name = "worker-${count.index}".

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Hard Call a module

Why: Modules package a tested pattern, like a VPC, for reuse.

What to do: Write module "vpc" with source = "terraform-aws-modules/vpc/aws", version = "5.8.1", name = "maruti-vpc" and cidr = "10.0.0.0/16".

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

Hard Remote state in S3

Why: Shared remote state with locking stops two people breaking each other.

What to do: Write a terraform block with backend "s3": bucket = "maruti-tfstate", key = "prod/terraform.tfstate", region = "ap-south-1", dynamodb_table = "tf-lock".

How:
  1. Write the block type (resource, variable, output, module...) and its labels in quotes.
  2. Open { and write each argument as name = value.
  3. Put text values in double quotes; numbers and true/false without quotes.
  4. Close every block with } and click Check answer.

See all DevOps practice tasks in the Task Hub →

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