Terraform AWS ALB Module and Patterns for Production Load Balancing

Infrastructure as code for AWS Application Load Balancers has become a standard operating procedure for teams that need repeatable, auditable, and version controlled networking. The terraform-aws-alb module provides a comprehensive overview for creating and managing AWS Application Load Balancers and Network Load Balancers through Terraform. The module offers a complete solution for provisioning load balancers in AWS with extensive configuration options and integration points. The terraform-aws-alb module enables users to provision AWS load balancers with a declarative Terraform configuration.

Terraform removes the manual click path through the AWS Console where an ALB requires a VPC, subnets, security groups, EC2 instances, a target group, and listeners. A small misconfiguration in any of those steps can break the whole setup. With Terraform the infrastructure is defined in code and provisioned with terraform apply. Need to rebuild the lab? Just run terraform apply again and you’re good to go.

Overview of terraform-aws-alb module

The module is described as a Terraform module which creates Application and Network Load Balancer resources on AWS. The module provides a complete solution for provisioning load balancers with extensive configuration options and integration points.

Key characteristics of the module approach:

Declarative provisioning of AWS load balancers
Support for both Application Load Balancer and Network Load Balancer resource types
Extensive configuration options and integration points
Management of associated target groups and listeners as part of the module boundary

A table summarizing the module scope is useful for teams evaluating reuse.

Capability	Description
Resource Type	Application Load Balancer and Network Load Balancer
Provisioning Model	Declarative Terraform configuration
Integration Points	Target groups, listeners, security groups, subnets
Configuration Depth	Extensive options for production load balancer setups

The module is positioned as an alternative to manual console builds. Instead of creating a VPC, configuring subnets, setting up security groups, launching Amazon EC2 instances, creating a target group, adding listeners, and then double checking everything, the module encapsulates the relationships.

Core capabilities and configuration

The Terraform Foundation module contains common configurations for an AWS Application Load Balancer running over HTTP/HTTPS. It is available through the Terraform registry.

Prerequisites for using the module include:

A Virtual Private Cloud and subnets where the ALB will be placed
One or more security groups to attach to the ALB
If HTTPS listener is planned, the ARN of an SSL certificate is required

The module supports both mutually exclusive modes:

Internal ALBs
External ALBs

Branch build status for the module is tracked with a master branch entry.

The module is designed to create a set of resources around an application load balancer, namely associated target groups and listeners. This aligns with the common workflow of provisioning an Application Load Balancer, launching EC2 instances, registering them in a target group, and testing load balancing by refreshing the ALB DNS and observing traffic alternate between instances.

The lab approach described for learning includes:

Provision an Application Load Balancer
Launch two EC2 instances
Register them in a target group
Test load balancing by refreshing the ALB DNS and observing traffic alternate

The diagram referenced highlights one of the powerful capabilities of an ALB routing traffic to different target groups using rules. This is commonly used for path-based routing for example /api vs /web or host-based routing in multi-service architectures.

Listener rules and routing constraints

When using ALB Listener rules, make sure that every rule's actions block ends in a forward, redirect, or fixed-response action so that every rule will resolve to some sort of an HTTP response.

ALB has the ability to replace what several ELBs can do by routing based on URI matchers. Additionally, operating at layer 7 opens the ability to shape traffic using WAF. AWS's documentation has a more exhaustive set of reasons. Alternatively, if using ALB with ECS look no further than the HashiCorp example.

A full example leveraging other community modules is contained in the examples/albtestfixture directory.

Terraform Foundation module specifics

The Terraform Foundation module emphasizes HTTP/HTTPS ALB patterns. Notes from the module documentation include operational coupling with autoscaling:

It's strongly recommended that the autoscaling module is instantiated in the same state as the ALB module as in flight changes to active target groups need to be propagated to the ASG immediately or will result in failure
The value of targetgroup[n][name] also must change any time there are modifications to existing targetgroups

This coupling is critical for production reliability. Changes to target groups must propagate immediately to the Auto Scaling Group or failures can occur.

The module documentation highlights layer 7 capabilities:

Feature	Benefit
URI based routing	Replace several ELBs with one ALB
Layer 7 operation	Enable traffic shaping using WAF
Listener rules	Forward, redirect, or fixed-response termination

Production architecture patterns with ASG

A production-style web architecture can follow real-world cloud and DevOps best practices. Instead of exposing EC2 instances directly to the internet, this project uses an Application Load Balancer in public subnets and Auto Scaling Group managed EC2 instances running in private subnets, with outbound internet access provided via a NAT Gateway.

The entire infrastructure is provisioned using Terraform as Infrastructure as Code.

Architecture Overview high-level flow:

Key design principles:

Only the ALB is public
EC2 instances live in private subnets
Auto Scaling Group ensures availability
NAT Gateway enables outbound access securely
Fully automated using Terraform

Tech Stack used in the reference architecture:

AWS VPC
AWS EC2
AWS Application Load Balancer
AWS Auto Scaling Group
AWS Internet Gateway
AWS NAT Gateway
Terraform Infrastructure as Code
Docker Application runtime
Nginx Demo web server

This architecture closely mirrors what is commonly used in production AWS environments.

Project structure and workflow

Keeping the structure clean matters a lot, especially once Terraform config starts growing. Create a project folder and place Terraform files inside it.

Common project layout for an ALB with ASG and networking:

alb.tf
asg.tf
network.tf
provider.tf
security_groups.tf
vpc.tf
userdata.sh
outputs.tf
.gitignore
README.md

Workflow steps referenced in learning labs:

Verify installation by running terraform -version
If Terraform is installed correctly, the version number will appear in your terminal
VS Code Setup for AWS ALB Terraform can use Visual Studio Code with Terraform extension for syntax highlighting, automatic formatting, basic validation
How Terraform Authenticates to AWS uses credentials configured in the AWS CLI when running terraform init, terraform plan, terraform apply

The lab emphasizes that after installation, verify that it’s working by running terraform -version.

Security and operational best practices

Security groups should allow traffic only from the ALB to improve security. ALB distributes traffic only to healthy targets.

Key takeaways from the hands-on lab:

Terraform makes AWS deployments faster and repeatable
ALB distributes traffic only to healthy targets
Using security groups to allow traffic only from the ALB improves security
terraform destroy makes cleanup easy

The advantage of Infrastructure as Code is no manual cleanup needed.

Conclusion

The terraform-aws-alb module and the surrounding Terraform patterns provide a repeatable foundation for provisioning Application Load Balancers and Network Load Balancers in AWS. The module enables declarative provisioning with extensive configuration options and integration points for target groups and listeners. Manual console builds are time consuming and error prone compared to code defined VPCs, subnets, security groups, EC2 instances, and ALBs that can be deployed with a few commands.

Production architectures benefit from placing the ALB in public subnets while keeping EC2 instances in private subnets behind a target group and Auto Scaling Group, with outbound internet via NAT Gateway. Only the ALB is public, instances live privately, and automation ensures availability.

Operational coupling between the ALB module and autoscaling module must be respected to avoid in flight failures when target groups change. Listener rules must always terminate in forward, redirect, or fixed-response actions to guarantee HTTP responses.

Overall, Infrastructure as Code simplifies real cloud setups by making deployments faster and repeatable, ensuring traffic is distributed only to healthy targets, and enabling easy cleanup with terraform destroy.