AWS ALB Query String, Host Header Redirects and Custom Header Routing

Pre-requisites

You need a Registered Domain in AWS Route53 to implement this usecase
Copy your terraform-key.pem file to terraform-manifests/private-key folder

Step-01: Introduction

We are going to implement four AWS ALB Application HTTPS Listener Rules
Rule-1 and Rule-2 will outline the Custom HTTP Header based Routing
Rule-3 and Rule-4 will outline the HTTP Redirect using Query String and Host Header based rules
Rule-1: custom-header=my-app-1 should go to App1 EC2 Instances
Rule-2: custom-header=my-app-2 should go to App2 EC2 Instances
Rule-3: When Query-String, website=aws-eks redirect to https://stacksimplify.com/aws-eks/
Rule-4: When Host Header = azure-aks.devopsincloud.com, redirect to https://stacksimplify.
Understand about Priority feature for Rules priority = 2

Step-02: c10-02-ALB-application-loadbalancer.tf

Define different HTTPS Listener Rules for ALB Load Balancer

Step-02-01: Rule-1: Custom Header Rule for App-1

Rule-1: custom-header=my-app-1 should go to App1 EC2 Instances

    # Rule-1: custom-header=my-app-1 should go to App1 EC2 Instances
    { 
      https_listener_index = 0
      priority = 1      
      actions = [
        {
          type               = "forward"
          target_group_index = 0
        }
      ]
      conditions = [{ 
        #path_patterns = ["/app1*"]
        #host_headers = [var.app1_dns_name]
        http_headers = [{
          http_header_name = "custom-header"
          values           = ["app-1", "app1", "my-app-1"]
        }]
      }]
    },

Step-02-02: Rule-2: Custom Header Rule for App-1

Rule-2: custom-header=my-app-2 should go to App2 EC2 Instances

    # Rule-2: custom-header=my-app-2 should go to App2 EC2 Instances    
    {
      https_listener_index = 0
      priority = 2      
      actions = [
        {
          type               = "forward"
          target_group_index = 1
        }
      ]
      conditions = [{
        #path_patterns = ["/app2*"] 
        #host_headers = [var.app2_dns_name]
        http_headers = [{
          http_header_name = "custom-header"
          values           = ["app-2", "app2", "my-app-2"]
        }]        
      }]
    },

Step-02-03: Rule-3: Query String Redirect

Rule-3: When Query-String, website=aws-eks redirect to https://stacksimplify.com/aws-eks/

  # Rule-3: When Query-String, website=aws-eks redirect to https://stacksimplify.com/aws-eks/
    { 
      https_listener_index = 0
      priority = 3
      actions = [{
        type        = "redirect"
        status_code = "HTTP_302"
        host        = "stacksimplify.com"
        path        = "/aws-eks/"
        query       = ""
        protocol    = "HTTPS"
      }]
      conditions = [{
        query_strings = [{
          key   = "website"
          value = "aws-eks"
          }]
      }]
    },

Step-02-04: Rule-4: Host Header Redirect

Rule-4: When Host Header = azure-aks.devopsincloud.com, redirect to https://stacksimplify.com/azure-aks/azure-kubernetes-service-introduction/

  # Rule-4: When Host Header = azure-aks.devopsincloud.com, redirect to https://stacksimplify.com/azure-aks/azure-kubernetes-service-introduction/
    { 
      https_listener_index = 0
      priority = 4
      actions = [{
        type        = "redirect"
        status_code = "HTTP_302"
        host        = "stacksimplify.com"
        path        = "/azure-aks/azure-kubernetes-service-introduction/"
        query       = ""
        protocol    = "HTTPS"
      }]
      conditions = [{
        host_headers = ["azure-aks11.devopsincloud.com"]
      }]
    },

Step-03: c12-route53-dnsregistration.tf

# DNS Registration 
## Default DNS
resource "aws_route53_record" "default_dns" {
  zone_id = data.aws_route53_zone.mydomain.zone_id 
  name    = "myapps11.devopsincloud.com"
  type    = "A"
  alias {
    name                   = module.alb.this_lb_dns_name
    zone_id                = module.alb.this_lb_zone_id
    evaluate_target_health = true
  }  
}

## Testing Host Header - Redirect to External Site from ALB HTTPS Listener Rules
resource "aws_route53_record" "app1_dns" {
  zone_id = data.aws_route53_zone.mydomain.zone_id 
  name    = "azure-aks11.devopsincloud.com"
  type    = "A"
  alias {
    name                   = module.alb.this_lb_dns_name
    zone_id                = module.alb.this_lb_zone_id
    evaluate_target_health = true
  }  
}

Step-04: Terraform ALB Module v6.0.0 Changes

Step-04-01: c10-02-ALB-application-loadbalancer.tf

# Before
  version = "5.16.0"

# After
  version = "6.0.0"

Step-04-02: c10-03-ALB-application-loadbalancer-outputs.tf

ALB Outpus Reference
this_ is removed from few of the outputs of ALB Module
So we can use the latest outputs from this section onwards
Update c10-03-ALB-application-loadbalancer-outputs.tf with latest outputs

output "lb_id" {
  description = "The ID and ARN of the load balancer we created."
  value       = module.alb.lb_id
}

output "lb_arn" {
  description = "The ID and ARN of the load balancer we created."
  value       = module.alb.lb_arn
}

output "lb_dns_name" {
  description = "The DNS name of the load balancer."
  value       = module.alb.lb_dns_name
}

output "lb_arn_suffix" {
  description = "ARN suffix of our load balancer - can be used with CloudWatch."
  value       = module.alb.lb_arn_suffix
}

output "lb_zone_id" {
  description = "The zone_id of the load balancer to assist with creating DNS records."
  value       = module.alb.lb_zone_id
}

output "http_tcp_listener_arns" {
  description = "The ARN of the TCP and HTTP load balancer listeners created."
  value       = module.alb.http_tcp_listener_arns
}

output "http_tcp_listener_ids" {
  description = "The IDs of the TCP and HTTP load balancer listeners created."
  value       = module.alb.http_tcp_listener_ids
}

output "https_listener_arns" {
  description = "The ARNs of the HTTPS load balancer listeners created."
  value       = module.alb.https_listener_arns
}

output "https_listener_ids" {
  description = "The IDs of the load balancer listeners created."
  value       = module.alb.https_listener_ids
}

output "target_group_arns" {
  description = "ARNs of the target groups. Useful for passing to your Auto Scaling group."
  value       = module.alb.target_group_arns
}

output "target_group_arn_suffixes" {
  description = "ARN suffixes of our target groups - can be used with CloudWatch."
  value       = module.alb.target_group_arn_suffixes
}

output "target_group_names" {
  description = "Name of the target group. Useful for passing to your CodeDeploy Deployment Group."
  value       = module.alb.target_group_names
}

output "target_group_attachments" {
  description = "ARNs of the target group attachment IDs."
  value       = module.alb.target_group_attachments
}

Step-04-03: c12-route53-dnsregistration.tf

# Before
    name                   = module.alb.this_lb_dns_name
    zone_id                = module.alb.this_lb_zone_id

# After
    name                   = module.alb.lb_dns_name
    zone_id                = module.alb.lb_zone_id

Step-05: Execute Terraform Commands

# Terraform Initialize
terraform init

# Terraform Validate
terraform validate

# Terraform Plan
terraform plan

# Terrform Apply
terraform apply -auto-approve

Step-06: Verify HTTP Header Based Routing (Rule-1 and Rule-2)

Rest Clinets we can use
https://restninja.io/
https://www.webtools.services/online-rest-api-client
https://reqbin.com/

# Verify Rule-1 and Rule-2
https://myapps.devopsincloud.com
custom-header = my-app-1  - Should get the page from App1 
custom-header = my-app-2  - Should get the page from App2

Step-07: Verify Rule-3

When Query-String, website=aws-eks redirect to https://stacksimplify.com/aws-eks/

# Verify Rule-3
https://myapps.devopsincloud.com/?website=aws-eks 
Observation: 
1. Should Redirect to https://stacksimplify.com/aws-eks/

Step-08: Verify Rule-4

When Host Header = azure-aks.devopsincloud.com, redirect to https://stacksimplify.com/azure-aks/azure-kubernetes-service-introduction/

# Verify Rule-4
http://azure-aks.devopsincloud.com
Observation: 
1. Should redirect to https://stacksimplify.com/azure-aks/azure-kubernetes-service-introduction/

Step-09: Clean-Up

# Destroy Resources
terraform destroy -auto-approve

# Delete Files
rm -rf .terraform*
rm -rf terraform.tfstate

References

Terraform AWS ALB