Deploying a Highly Available AWS Architecture with Terraform
Source: Dev.to
High availability is one of those concepts everyone mentions, but far fewer people actually implement correctly. In many demo projects, availability stops at launching an EC2 instance and exposing it to the internet. That works until something breaks, and in production something always breaks. In this post, I walk through a Terraform project where the primary goal is resilience. The architecture is designed to keep serving traffic even when individual instances or an entire Availability Zone fails. The full source code is available here:
https://github.com/Copubah/Terraform-AWS-Multi-AZ-Highly-Available-Architecture Why I Built This Project I wanted a project that answers practical questions instead of just showing that something is running. This project focuses on those questions using Terraform as the single source of truth for infrastructure. High Level Architecture At a high level, the architecture follows a common and proven AWS pattern.
User traffic enters through an Application Load Balancer deployed in public subnets. The load balancer distributes traffic to application instances running in private subnets across multiple Availability Zones. An Auto Scaling Group ensures that capacity is always maintained. Supporting networking components like NAT Gateways and route tables ensure instances can communicate outbound without being publicly exposed. Every major component is spread across at least two Availability Zones to eliminate single points of failure. Core AWS Components Used VPC
A custom VPC provides full control over networking. DNS support and hostnames are enabled to support internal service discovery and load balancing. Subnets
Public subnets host the Application Load Balancer and NAT Gateways. Private subnets host the EC2 instances. Subnets are evenly distributed across Availability Zones to ensure redundancy. Application Load Balancer
The ALB acts as the entry point to the system. It performs health checks on backend instances and only routes traffic to healthy targets. If an instance fails health checks, it is automatically removed from rotation. Auto Scaling Group
The Auto Scaling Group maintains a minimum number of EC2 instances across multiple Availability Zones. If an instance terminates or becomes unhealthy, Auto Scaling replaces it automatically. This is one of the key pieces that enables self healing behavior. Security Groups
Security groups are tightly scoped. The load balancer allows inbound HTTP traffic from the internet. Application instances only allow inbound traffic from the load balancer. This reduces the attack surface and follows least privilege principles. Terraform and Modularity One of the main goals of this project was clean Terraform structure. Instead of placing everything in a single main.tf file, the infrastructure is broken into reusable modules. Each module is responsible for a single concern such as networking, load balancing, or compute. This mirrors how Terraform is used in real teams and makes the code easier to reason about. Each module contains its own variables and outputs, which keeps dependencies explicit and avoids hidden coupling. The root module simply wires everything together. This modular approach also makes future expansion straightforward. Adding a database layer or extending to multi region deployments would not require restructuring the existing code. Failure Scenarios and How the Architecture Responds Instance failure
If an EC2 instance crashes or is terminated, the load balancer stops sending traffic to it. The Auto Scaling Group detects the capacity drop and launches a replacement instance automatically. Availability Zone failure
If an entire Availability Zone becomes unavailable, the load balancer routes traffic only to healthy instances in the remaining zones. Auto Scaling launches new instances in available zones to maintain capacity. Traffic spikes
Auto Scaling policies can be added to scale out based on load. The architecture already supports horizontal scaling without any redesign. Infrastructure rebuild
Because everything is defined in Terraform, the entire environment can be destroyed and recreated consistently. This is critical for disaster recovery and reproducibility.
Why This Makes a Strong Portfolio Project This project focuses on reliability rather than visual complexity. It demonstrates understanding of core AWS concepts such as Availability Zones, load balancing, self healing infrastructure, and infrastructure as code. It also shows discipline in Terraform usage through modular design, clear variable definitions, and reproducibility. These are the qualities teams look for when reviewing real world infrastructure code. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse - What happens if an EC2 instance crashes
- What happens if an Availability Zone becomes unavailable
- How fast can the environment be rebuilt from scratch
- How cleanly is the infrastructure defined and reused
