Application Gateway (Layer 7) in Azure - Mini Project: Build & Apply

Create an Azure Application Gateway (Layer 7)

📖 Scenario: You are setting up a web application in Azure that needs a secure and scalable entry point. To manage traffic and provide features like SSL termination and URL-based routing, you will create an Azure Application Gateway, which works at Layer 7 (the application layer).

🎯 Goal: Build an Azure Application Gateway with a frontend IP configuration, backend pool, HTTP settings, and a basic routing rule to direct traffic to the backend pool.

📋 What You'll Learn

Create a resource group variable named resource_group with the value "MyResourceGroup".

Create an Application Gateway configuration variable named app_gateway_config with the basic settings.

Add a backend pool named backend_pool with one backend IP address "10.0.1.4".

Add a routing rule named routing_rule that connects the frontend IP to the backend pool using HTTP settings.

💡 Why This Matters

🌍 Real World

Application Gateways are used in real-world cloud deployments to manage web traffic securely and efficiently, providing features like load balancing, SSL termination, and web application firewall.

💼 Career

Understanding how to configure Application Gateways is essential for cloud engineers and architects working with Azure to build scalable and secure web applications.

1

Create the resource group variable

Create a variable called resource_group and set it to the string "MyResourceGroup".

Azure

# Your code here

Hint

Use a simple string assignment to create the resource group variable.

2

Define the basic Application Gateway configuration

Create a dictionary called app_gateway_config with keys "name" set to "myAppGateway", "location" set to "eastus", and "sku" set to "Standard_v2".

Azure

resource_group = "MyResourceGroup"
# Your code here

Hint

Use a dictionary with the exact keys and values as specified.

3

Add a backend pool with one backend IP address

Add a key "backend_pools" to app_gateway_config with a list containing one dictionary. This dictionary should have the key "name" set to "backend_pool" and "backend_addresses" set to a list with one dictionary containing "ip_address" set to "10.0.1.4".

Azure

resource_group = "MyResourceGroup"
app_gateway_config = {
    "name": "myAppGateway",
    "location": "eastus",
    "sku": "Standard_v2"
}
# Your code here

Hint

Remember to add the backend_pools key with a list of dictionaries as described.

4

Add a routing rule connecting frontend IP to backend pool

Add keys "frontend_ip_config", "http_settings", and "routing_rule" to app_gateway_config. Set "frontend_ip_config" to a dictionary with "name" as "frontendIP" and "public_ip_address" as "20.30.40.50". Set "http_settings" to a dictionary with "name" as "httpSettings" and "port" as 80. Set "routing_rule" to a dictionary with "name" as "rule1", "frontend_ip_config" as "frontendIP", "backend_pool" as "backend_pool", and "http_settings" as "httpSettings".

Azure

resource_group = "MyResourceGroup"
app_gateway_config = {
    "name": "myAppGateway",
    "location": "eastus",
    "sku": "Standard_v2",
    "backend_pools": [
        {
            "name": "backend_pool",
            "backend_addresses": [
                {"ip_address": "10.0.1.4"}
            ]
        }
    ]
}
# Your code here

Hint

Add the frontend_ip_config, http_settings, and routing_rule keys exactly as described to complete the Application Gateway configuration.

Practice

1. What is the main function of an Azure Application Gateway at Layer 7?

easy

A. It stores data in a scalable database.

B. It manages virtual machines in a subnet.

C. It routes web traffic based on URL paths and content.

D. It provides DNS resolution for domain names.

Solution

1. Step 1: Understand Layer 7 role

   Layer 7 means the application layer, which handles web traffic content like URLs.

2. Step 2: Identify Application Gateway function

   Application Gateway routes traffic based on URL paths and content, unlike DNS or VM management.

3. Final Answer:

   It routes web traffic based on URL paths and content. -> Option C

4. Quick Check:

   Layer 7 routing = URL-based traffic routing [OK]

Hint: Layer 7 means web content routing, not VM or DNS tasks [OK]

Common Mistakes:

• Confusing Application Gateway with DNS or VM services
• Thinking it works at network layer instead of application layer
• Assuming it stores data like a database

2. Which of the following is the correct way to define a frontend IP configuration for an Azure Application Gateway in ARM template JSON?

easy

A. {\"name\": \"appGatewayFrontendIP\", \"properties\": {\"publicIPAddress\": {\"id\": \"/subscriptions/.../publicIPAddresses/myPublicIP\"}}}

B. {\"name\": \"appGatewayFrontendIP\", \"location\": \"eastus\"}

C. {\"frontendIP\": \"myPublicIP\"}

D. {\"ipConfig\": {\"publicIP\": \"myPublicIP\"}}

Solution

1. Step 1: Review ARM template frontend IP syntax

   The frontend IP config requires a name and properties including a reference to a public IP resource by its ID.

2. Step 2: Match correct JSON structure

   {\"name\": \"appGatewayFrontendIP\", \"properties\": {\"publicIPAddress\": {\"id\": \"/subscriptions/.../publicIPAddresses/myPublicIP\"}}} correctly uses "name" and "properties" with "publicIPAddress" and its "id" field, matching ARM schema.

3. Final Answer:

   {"name": "appGatewayFrontendIP", "properties": {"publicIPAddress": {"id": "/subscriptions/.../publicIPAddresses/myPublicIP"}}} -> Option A

4. Quick Check:

   Frontend IP config needs name + publicIPAddress id [OK]

Hint: Look for 'properties' with 'publicIPAddress' and 'id' fields [OK]

Common Mistakes:

• Missing 'properties' wrapper around publicIPAddress
• Using 'location' inside frontend IP config incorrectly
• Incorrect field names like 'frontendIP' or 'ipConfig'

3. Given this simplified ARM snippet for an Application Gateway backend HTTP settings, what will be the effect of setting "pickHostNameFromBackendAddress" to true?

{
  "name": "appGatewayBackendHttpSettings",
  "properties": {
    "port": 80,
    "protocol": "Http",
    "pickHostNameFromBackendAddress": true
  }
}

medium

A. The backend hostname is taken from the backend pool IP or FQDN instead of the HTTP settings.

B. The Application Gateway ignores the backend pool and uses the frontend hostname.

C. The backend HTTP settings port is ignored and defaults to 443.

D. The Application Gateway disables SSL termination.

Solution

1. Step 1: Understand 'pickHostNameFromBackendAddress'

   This setting tells the gateway to use the hostname from the backend pool's address (IP or FQDN) for HTTP requests.

2. Step 2: Analyze effect on backend requests

   When true, the hostname in HTTP headers matches backend pool address, not the HTTP settings hostname.

3. Final Answer:

   The backend hostname is taken from the backend pool IP or FQDN instead of the HTTP settings. -> Option A

4. Quick Check:

   pickHostNameFromBackendAddress true = use backend pool hostname [OK]

Hint: True means use backend pool hostname, not HTTP settings hostname [OK]

Common Mistakes:

• Thinking it changes port or protocol
• Confusing frontend hostname with backend hostname
• Assuming it disables SSL termination

4. You deployed an Application Gateway but it fails to route traffic to backend servers. The backend pool uses IP addresses, but the health probes always fail. What is a likely cause?

medium

A. The Application Gateway subnet is too large.

B. The backend HTTP settings have 'pickHostNameFromBackendAddress' set to true but backend IPs lack proper DNS names.

C. The frontend IP configuration is missing a public IP address.

D. The backend pool uses FQDNs instead of IP addresses.

Solution

1. Step 1: Understand health probe failure with IP backend pool

   If 'pickHostNameFromBackendAddress' is true, the gateway uses backend hostname from IP, which fails if no DNS name exists.

2. Step 2: Identify mismatch causing probe failure

   Backend IPs lack DNS names, so probes fail when hostname is required but missing.

3. Final Answer:

   The backend HTTP settings have 'pickHostNameFromBackendAddress' set to true but backend IPs lack proper DNS names. -> Option B

4. Quick Check:

   IP backend + pickHostNameFromBackendAddress true = probe fails [OK]

Hint: Check if backend IPs have DNS names when pickHostNameFromBackendAddress is true [OK]

Common Mistakes:

• Blaming subnet size for routing issues
• Assuming frontend IP config missing public IP causes backend probe failure
• Confusing backend pool IPs with FQDNs

5. You want to configure an Azure Application Gateway to route requests to different backend pools based on URL paths: /images/* to an image server pool and /api/* to an API server pool. Which configuration step is essential to achieve this?

hard

A. Configure the backend HTTP settings to use HTTPS only.

B. Assign multiple public IP addresses to the frontend configuration.

C. Use multiple frontend ports with the same backend pool.

D. Create path-based routing rules with URL path maps specifying backend pools for each path.

Solution

1. Step 1: Understand URL-based routing requirement

   Routing based on URL paths requires path-based routing rules with URL path maps.

2. Step 2: Configure path-based rules

   Define URL path maps that link specific URL patterns like '/images/*' and '/api/*' to their respective backend pools.

3. Final Answer:

   Create path-based routing rules with URL path maps specifying backend pools for each path. -> Option D

4. Quick Check:

   URL path routing = path-based rules with URL maps [OK]

Hint: Use path-based routing rules with URL maps for URL path routing [OK]

Common Mistakes:

• Thinking multiple public IPs are needed for URL routing
• Using multiple frontend ports without path rules
• Assuming backend HTTP settings control URL routing