DTOSS-11302: Application health check

To ensure that the application is avaiable we need to turn on the application health check on application insights.
This involves
Creating a health check restful endpoint on both web app container.
Creating the monitor on application insights that tests that the web app container is up.

Author: mrlockstar

infrastructure/modules/app-service-plan/variables.tf

@@ -203,9 +203,9 @@ variable "alert_cpu_threshold" {
 }
 
 variable "alert_memory_threshold" {
-  type    = number
+  type        = number
   description = "If alerting is enabled this will control what the memory threshold will be, default will be 80."
-  default = 80
+  default     = 80
 }
 
 variable "alert_window_size" {

infrastructure/modules/application-insights-availability-test/README.md

@@ -0,0 +1,26 @@
+# Application Insights availability test
+
+Deploy an [Azure application insights avaliability test](https://learn.microsoft.com/en-us/azure/azure-monitor/app/availability?tabs=standard) to continuously monitor the accessibility of a web endpoint. The test periodically sends requests to a specified URL from multiple Azure locations and records response times, status codes, and any failures.
+
+The availability test runs automatically at the configured frequency once deployed and provides visibility into uptime, latency, and dependency issues through [Application insights](https://learn.microsoft.com/en-us/azure/azure-monitor/app/usage?tabs=users) and Azure Monitor.
+Integrates with the  module.
+
+See also the following ADO template step that can be used to verify endpoint health as part of a release pipeline: app-insights-availability-check.yaml.
+
+
+## Terraform documentation
+For the list of inputs, outputs, resources... check the [terraform module documentation](tfdocs.md).
+
+## Usage
+Create the application Insights availability test:
+```hcl
+module "azurerm_application_insights_standard_web_test" {
+  source = "../dtos-devops-templates/infrastructure/modules/application-insights-availability-test"
+
+  name                       = "${var.app_short_name}-web-${var.environment}"
+  resource_group_name        = var.resource_group_name_infra
+  location                   = var.location
+  application_insights_id    = data.azurerm_log_analytics_workspace.audit[0].id
+  target_url                 = "${module.container-apps[0].external_url}healthcheck/"
+}
+```

infrastructure/modules/application-insights-availability-test/main.tf

@@ -0,0 +1,16 @@
+resource "azurerm_application_insights_standard_web_test" "this" {
+  name = var.name
+
+  location                = var.location
+  resource_group_name     = var.resource_group_name
+  application_insights_id = var.application_insights_id
+
+  frequency = var.frequency
+  timeout   = var.timeout
+
+  request {
+    url = var.target_url
+  }
+
+  geo_locations = var.geo_locations
+}

infrastructure/modules/application-insights-availability-test/tfdocs.md

@@ -0,0 +1,82 @@
+# Module documentation
+
+## Required Inputs
+
+The following input variables are required:
+
+### <a name="input_application_insights_id"></a> [application\_insights\_id](#input\_application\_insights\_id)
+
+Description: The Application Insights resource id to associate the availability test with
+
+Type: `string`
+
+### <a name="input_name"></a> [name](#input\_name)
+
+Description: Name of the availability test, must be unique for the used application insights instance
+
+Type: `string`
+
+### <a name="input_resource_group_name"></a> [resource\_group\_name](#input\_resource\_group\_name)
+
+Description: The name of the resource group in which to create the availability test.
+
+Type: `string`
+
+## Optional Inputs
+
+The following input variables are optional (have default values):
+
+### <a name="input_frequency"></a> [frequency](#input\_frequency)
+
+Description: Frequency of test in seconds
+
+Type: `number`
+
+Default: `300`
+
+### <a name="input_geo_locations"></a> [geo\_locations](#input\_geo\_locations)
+
+Description: List of Azure test locations (provider-specific location strings for UK and Ireland)
+
+Type: `list(string)`
+
+Default:
+
+```json
+[
+  "emea-ru-msa-edge",
+  "emea-se-sto-edge",
+  "emea-gb-db3-azr"
+]
+```
+
+### <a name="input_location"></a> [location](#input\_location)
+
+Description: The location/region where the availability test is deployed (must match App Insights location)
+
+Type: `string`
+
+Default: `"UK South"`
+
+### <a name="input_target_url"></a> [target\_url](#input\_target\_url)
+
+Description: The target URL for the restful endpoint to hit to validate the application is avaliable
+
+Type: `string`
+
+Default: `""`
+
+### <a name="input_timeout"></a> [timeout](#input\_timeout)
+
+Description: Timeout in seconds
+
+Type: `number`
+
+Default: `30`
+
+
+## Resources
+
+The following resources are used by this module:
+
+- [azurerm_application_insights_standard_web_test.this](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/application_insights_standard_web_test) (resource)

infrastructure/modules/application-insights-availability-test/variables.tf

@@ -0,0 +1,51 @@
+variable "name" {
+  type        = string
+  description = "Name of the availability test, must be unique for the used application insights instance"
+}
+
+variable "resource_group_name" {
+  description = "The name of the resource group in which to create the availability test."
+  type        = string
+  validation {
+    condition     = can(regex("^[a-zA-Z0-9-]{1,255}$", var.resource_group_name))
+    error_message = "The resource group name must be between 1 and 255 characters and can only contain alphanumeric characters, hyphens, and underscores."
+  }
+}
+
+variable "location" {
+  type        = string
+  description = "The location/region where the availability test is deployed (must match App Insights location)"
+  default     = "UK South"
+}
+
+variable "application_insights_id" {
+  type        = string
+  description = "The Application Insights resource id to associate the availability test with"
+}
+
+variable "frequency" {
+  type        = number
+  default     = 300
+  validation {
+    condition     = contains(["300", "600", "900"], var.frequency)
+    error_message = "The frequency must be one of: 300, 600 or 900"
+  }
+  description = "Frequency of test in seconds, defaults to 300."
+}
+
+variable "timeout" {
+  type        = number
+  default     = 30
+  description = "Timeout in seconds, defaults to 30."
+}
+
+variable "geo_locations" {
+  type        = list(string)
+  default     = ["emea-ru-msa-edge", "emea-se-sto-edge", "emea-gb-db3-azr"]
+  description = "List of Azure test locations (provider-specific location strings for UK and Ireland)"
+}
+
+variable "target_url" {
+  type        = string
+  description = "The target URL for the restful endpoint to hit to validate the application is available"
+}

infrastructure/modules/function-app/alerts.tf

@@ -4,7 +4,7 @@ resource "azurerm_monitor_metric_alert" "function_4xx" {
 
   name                = "${azurerm_linux_function_app.function_app.name}-4xx-errors"
   resource_group_name = var.resource_group_name_monitoring != null ? var.resource_group_name_monitoring : var.resource_group_name
-  scopes              = [azurerm_linux_function_app.function_app.id]  # Point to your function app
+  scopes              = [azurerm_linux_function_app.function_app.id] # Point to your function app
   description         = "Action will be triggered when 4xx errors exceed ${var.alert_4xx_threshold}"
   window_size         = var.alert_window_size
   frequency           = local.alert_frequency
@@ -13,7 +13,7 @@ resource "azurerm_monitor_metric_alert" "function_4xx" {
   criteria {
     metric_namespace = "Microsoft.Web/sites"
     metric_name      = "Http4xx"
-    aggregation      = "Total"  # Count total 4xx errors
+    aggregation      = "Total" # Count total 4xx errors
     operator         = "GreaterThan"
     threshold        = var.alert_4xx_threshold
   }
@@ -35,7 +35,7 @@ resource "azurerm_monitor_metric_alert" "function_5xx" {
 
   name                = "${azurerm_linux_function_app.function_app.name}-5xx-errors"
   resource_group_name = var.resource_group_name_monitoring != null ? var.resource_group_name_monitoring : var.resource_group_name
-  scopes              = [azurerm_linux_function_app.function_app.id]  # Point to your function app
+  scopes              = [azurerm_linux_function_app.function_app.id] # Point to your function app
   description         = "Action will be triggered when 5xx errors exceed ${var.alert_5xx_threshold}"
   window_size         = var.alert_window_size
   frequency           = local.alert_frequency
@@ -44,7 +44,7 @@ resource "azurerm_monitor_metric_alert" "function_5xx" {
   criteria {
     metric_namespace = "Microsoft.Web/sites"
     metric_name      = "Http5xx"
-    aggregation      = "Total"  # Count total 5xx errors
+    aggregation      = "Total" # Count total 5xx errors
     operator         = "GreaterThan"
     threshold        = var.alert_5xx_threshold
   }

infrastructure/modules/function-app/tfdocs.md

@@ -122,6 +122,38 @@ Type: `any`
 
 Default: `null`
 
+### <a name="input_action_group_id"></a> [action\_group\_id](#input\_action\_group\_id)
+
+Description: The ID of the Action Group to use for alerts.
+
+Type: `string`
+
+Default: `null`
+
+### <a name="input_alert_4xx_threshold"></a> [alert\_4xx\_threshold](#input\_alert\_4xx\_threshold)
+
+Description: The threshold for 4xx errors to trigger the alert.
+
+Type: `number`
+
+Default: `10`
+
+### <a name="input_alert_5xx_threshold"></a> [alert\_5xx\_threshold](#input\_alert\_5xx\_threshold)
+
+Description: The threshold for 4xx errors to trigger the alert.
+
+Type: `number`
+
+Default: `10`
+
+### <a name="input_alert_window_size"></a> [alert\_window\_size](#input\_alert\_window\_size)
+
+Description: The period of time that is used to monitor alert activity e.g. PT1M, PT5M, PT15M, PT30M, PT1H, PT6H, PT12H. The interval between checks is adjusted accordingly.
+
+Type: `string`
+
+Default: `"PT5M"`
+
 ### <a name="input_always_on"></a> [always\_on](#input\_always\_on)
 
 Description: Should the Function App be always on. Override standard default.
@@ -168,6 +200,14 @@ Default:
 ]
 ```
 
+### <a name="input_enable_alerting"></a> [enable\_alerting](#input\_enable\_alerting)
+
+Description: Whether monitoring and alerting is enabled for the App Service Plan.
+
+Type: `bool`
+
+Default: `false`
+
 ### <a name="input_entra_id_group_ids"></a> [entra\_id\_group\_ids](#input\_entra\_id\_group\_ids)
 
 Description: n/a
@@ -311,6 +351,22 @@ list(object({
 
 Default: `[]`
 
+### <a name="input_resource_group_name_monitoring"></a> [resource\_group\_name\_monitoring](#input\_resource\_group\_name\_monitoring)
+
+Description: The name of the resource group in which to create the Monitoring resources for the App Service Plan. Changing this forces a new resource to be created.
+
+Type: `string`
+
+Default: `null`
+
+### <a name="input_severity"></a> [severity](#input\_severity)
+
+Description: Severity of the alert. 0 = Critical, 1 = Error, 2 = Warning, 3 = Informational, 4 = Verbose. Default is 3.
+
+Type: `number`
+
+Default: `3`
+
 ### <a name="input_storage_account_access_key"></a> [storage\_account\_access\_key](#input\_storage\_account\_access\_key)
 
 Description: The Storage Account Primary Access Key.
@@ -402,3 +458,5 @@ The following resources are used by this module:
 
 - [azuread_group_member.function_app](https://registry.terraform.io/providers/hashicorp/azuread/latest/docs/resources/group_member) (resource)
 - [azurerm_linux_function_app.function_app](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/linux_function_app) (resource)
+- [azurerm_monitor_metric_alert.function_4xx](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/monitor_metric_alert) (resource)
+- [azurerm_monitor_metric_alert.function_5xx](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/monitor_metric_alert) (resource)