What is Azure Application Gateway Terraform?
Azure Application Gateway Terraform means defining and deploying Azure Application Gateway with infrastructure as code
instead of clicking through the Azure portal manually. The main Terraform resource is azurerm_application_gateway,
and it allows you to describe listeners, frontend IPs, frontend ports, backend pools, probes, backend HTTP settings,
redirect rules, URL path maps, and WAF-related configuration in a repeatable way.
Why Terraform is used for Azure Application Gateway
Application Gateway configurations can become large and error-prone when teams manage them manually. Terraform helps engineering teams standardize how listeners, pools, probes, certificates, and routing rules are created across development, test, and production environments.
Consistency
The same architecture can be deployed across multiple environments without rebuilding the gateway by hand.
Reviewability
Engineers can review Application Gateway changes through pull requests before they reach production.
Scalability
Teams can build reusable modules so multiple services use the same routing and security standards.
Azure Application Gateway Terraform explained with the 5 Ws + How
This keeps the page useful for beginners, engineers building the service, and interview learners looking for practical understanding.
What
Terraform-based deployment of Azure Application Gateway using AzureRM provider resources.
Why
To manage listeners, probes, backend pools, routing rules, and WAF-ready design in a repeatable way.
When
Use it when application delivery infrastructure must be consistent across environments or managed through CI/CD.
Where
Inside Azure VNets, usually with supporting resources like subnet, public IP, NSG, and backend application services.
Who
DevOps engineers, platform teams, cloud engineers, and security-conscious infrastructure teams.
How
Terraform defines Azure resources declaratively, and the Azure provider creates the Application Gateway based on that desired state.
Prerequisites before writing the Terraform
Azure Application Gateway usually depends on supporting infrastructure. A clean design starts with knowing what must already exist and what should be created together.
Common prerequisites
- Azure subscription and Terraform AzureRM provider
- Resource group
- Virtual network
- Dedicated subnet for Application Gateway
- Public IP if internet-facing
- Backend targets such as VMs, VM Scale Sets, private services, or ingress endpoints
Production planning items
- Frontend hostname and DNS plan
- TLS certificate approach
- Probe path design
- NSG and route table review
- WAF decision
- Environment naming conventions
Terraform resource model for Azure Application Gateway
One reason this resource feels complex is that many real Azure Application Gateway parts are nested inside a single Terraform resource. Understanding the mapping makes the code easier to maintain.
| Terraform block | Azure concept | Purpose |
|---|---|---|
gateway_ip_configuration |
Gateway subnet attachment | Places the gateway into the correct subnet |
frontend_ip_configuration |
Frontend IP | Defines public or private entry IP |
frontend_port |
Port listener entry | Usually 80 or 443 |
backend_address_pool |
Backend pool | Defines where traffic is sent |
backend_http_settings |
Backend connection settings | Defines protocol, port, affinity, timeout |
probe |
Health probe | Checks backend application health |
http_listener |
Listener | Accepts frontend HTTP/HTTPS traffic |
request_routing_rule |
Routing rule | Maps listener to backend target and behavior |
ssl_certificate |
TLS certificate | Used for HTTPS termination |
waf_configuration |
WAF settings | Enables application-layer security features |
Recommended code structure
For real projects, do not keep everything in one giant Terraform file forever. Start simple, but grow toward a reusable layout.
terraform/
├── main.tf
├── variables.tf
├── outputs.tf
├── providers.tf
├── terraform.tfvars
└── modules/
└── application-gateway/
├── main.tf
├── variables.tf
└── outputs.tf
Root module
Connects shared network resources, naming, and environment-specific values.
Reusable child module
Encapsulates the Application Gateway logic so multiple environments stay consistent.
Variables and outputs
Keep certificate values, backend IPs, ports, names, and environment settings cleanly separated.
Terraform example for Azure Application Gateway
This example shows a practical starter pattern for Azure Application Gateway using Terraform. It is intentionally readable and structured to help engineers understand how Azure concepts map into code.
terraform {
required_version = ">= 1.5.0"
required_providers {
azurerm = {
source = "hashicorp/azurerm"
version = ">= 3.100.0"
}
}
}
provider "azurerm" {
features {}
}
resource "azurerm_resource_group" "rg" {
name = "rg-appgw-prod-san-1"
location = "South Africa North"
}
resource "azurerm_virtual_network" "vnet" {
name = "vnet-appgw-prod-san-1"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
address_space = ["10.40.0.0/16"]
}
resource "azurerm_subnet" "appgw_subnet" {
name = "snet-appgw-prod-san-1"
resource_group_name = azurerm_resource_group.rg.name
virtual_network_name = azurerm_virtual_network.vnet.name
address_prefixes = ["10.40.10.0/24"]
}
resource "azurerm_public_ip" "appgw_pip" {
name = "pip-appgw-prod-san-1"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
allocation_method = "Static"
sku = "Standard"
}
resource "azurerm_application_gateway" "appgw" {
name = "appgw-prod-san-1"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
sku {
name = "WAF_v2"
tier = "WAF_v2"
capacity = 2
}
gateway_ip_configuration {
name = "gateway-ip-config"
subnet_id = azurerm_subnet.appgw_subnet.id
}
frontend_port {
name = "frontend-https"
port = 443
}
frontend_ip_configuration {
name = "frontend-public"
public_ip_address_id = azurerm_public_ip.appgw_pip.id
}
backend_address_pool {
name = "backend-pool-web"
ip_addresses = ["10.40.20.10", "10.40.20.11"]
}
probe {
name = "probe-https"
protocol = "Https"
path = "/health"
host = "app.example.com"
interval = 30
timeout = 30
unhealthy_threshold = 3
pick_host_name_from_backend_http_settings = false
minimum_servers = 0
match {
status_code = ["200-399"]
}
}
backend_http_settings {
name = "backend-https-settings"
cookie_based_affinity = "Disabled"
path = "/"
port = 443
protocol = "Https"
request_timeout = 60
probe_name = "probe-https"
pick_host_name_from_backend_address = false
host_name = "app.example.com"
}
ssl_certificate {
name = "tls-cert"
data = filebase64("certificate.pfx")
password = var.pfx_password
}
http_listener {
name = "listener-https"
frontend_ip_configuration_name = "frontend-public"
frontend_port_name = "frontend-https"
protocol = "Https"
ssl_certificate_name = "tls-cert"
host_name = "app.example.com"
}
request_routing_rule {
name = "rule-https-basic"
rule_type = "Basic"
http_listener_name = "listener-https"
backend_address_pool_name = "backend-pool-web"
backend_http_settings_name = "backend-https-settings"
priority = 100
}
waf_configuration {
enabled = true
firewall_mode = "Prevention"
rule_set_type = "OWASP"
rule_set_version = "3.2"
}
}
variable "pfx_password" {
description = "Password for the PFX certificate"
type = string
sensitive = true
}
How the Terraform code maps to the real Azure service
Many engineers can paste Terraform, but not everyone understands how each section maps to the running Application Gateway. This section makes that relationship clear.
Network placement
azurerm_subnet.appgw_subnet and gateway_ip_configuration together place the gateway inside the correct Azure subnet.
Public entry
azurerm_public_ip.appgw_pip and frontend_ip_configuration expose the entry point to clients.
Traffic intake
frontend_port plus http_listener define how HTTPS traffic is accepted and which hostname and certificate are used.
Backend routing
backend_address_pool, backend_http_settings, and request_routing_rule define where traffic goes and how.
Health
probe checks the actual application health path so unhealthy backends stop receiving traffic.
Security
waf_configuration and ssl_certificate add application-layer protection and HTTPS support.
Real-world Azure Application Gateway Terraform use cases
Practical examples make this page more useful and help avoid duplicate, generic Terraform content.
Multi-environment rollout
A platform team deploys the same Application Gateway pattern to dev, sit, uat, and prod using environment variables and module reuse.
AKS north-south entry
Terraform provisions a consistent application entry layer in front of Kubernetes-hosted services while keeping the design reviewable in Git.
Centralized WAF deployment
Security teams standardize WAF-enabled gateways and ensure listeners, TLS settings, and backend health patterns are applied uniformly.
Terraform vs manual Azure portal deployment
Both approaches can work, but Terraform becomes more valuable as environments and rule complexity grow.
| Approach | Best for | Strength | Weakness |
|---|---|---|---|
| Terraform | Repeatable production deployments | Version control, consistency, reviewable changes | More setup and structure required at the start |
| Azure Portal | One-off testing or learning | Easy for quick initial exploration | Hard to reproduce accurately across environments |
Best practices
Practical guidance is one of the things that makes a page feel premium and useful to working engineers.
Use a module for repeatability
Keep the Application Gateway logic reusable instead of copying and editing large blocks in every environment.
Name blocks clearly
Use consistent names for listeners, probes, ports, and pools so rule mapping stays readable.
Match probes to real health endpoints
Probe the application health path, not just the root page, if your service has a proper readiness endpoint.
Keep certificate handling deliberate
Document where the certificate comes from, how it is rotated, and whether the gateway terminates or re-encrypts TLS.
Separate variables from code
Use variables and tfvars for environment-specific values like hostnames, backend IPs, and passwords.
Validate supporting network design
Subnet, NSG, route table, DNS, and backend reachability must all be correct or the gateway will appear broken.
Common mistakes
Provider-specific mistakes help avoid thin, duplicate content and make the page practical in the Azure context.
Wrong subnet assumptions
Engineers often forget that Application Gateway subnet planning matters and cannot just be treated like any random subnet.
Probe misconfiguration
A wrong host header, path, port, or protocol can make healthy applications look unhealthy.
Listener-rule mismatch
If listeners, ports, backend settings, and routing rules do not align, traffic does not flow as expected.
Hardcoding too much
Putting all names, backend IPs, and certificate assumptions directly in one file makes the deployment brittle.
Ignoring backend HTTP settings
Timeout, protocol, affinity, and host header settings are easy to overlook but often cause real failures.
No internal structure
Large hand-written blocks without module design become difficult to manage as soon as multiple apps share the gateway.
Frequently asked questions
FAQ sections help capture real search intent and make the resource page more complete.
What Terraform resource is used for Azure Application Gateway?
The main resource is azurerm_application_gateway.
Can I deploy WAF with Azure Application Gateway in Terraform?
Yes. WAF-related settings can be defined inside the Application Gateway configuration, depending on the design and provider support.
Do I need a dedicated subnet for Azure Application Gateway?
Application Gateway subnet planning is important, and teams should design it intentionally rather than placing the resource without network review.
Should I use Terraform modules for Application Gateway?
Yes, especially when you have multiple environments or similar gateway patterns across teams.
What usually breaks first in Application Gateway Terraform deployments?
Probes, listener mappings, backend settings, subnet assumptions, and certificate handling are the most common problem areas.