Az Function Elastic Premium - Azure Functions runtime is unreachable - azure

Question

I have an Azure function that I need to run in an Elastic Premium plan. After deployed I see the following error:
Azure Functions runtime is unreachable
I've tried to solve it following Microsoft documentation, no luck.
Here is some thoughts about my tries :
We checked the Storage account is created
The Function's subnet already has the service endpoint for the storage account
Vnet integration is already enabled in the Function and it (subnet) is already added to the Storage firewall
We added the required properties in the Function settings:
WEBSITE_CONTENTAZUREFILECONNECTIONSTRING = dynamic created (connection string to the
Storage account)
WEBSITE_CONTENTOVERVNET = 1
WEBSITE_CONTENTSHARE = dynamic created
WEBSITE_VNET_ROUTE_ALL = 1
Here is the documentation link.
https://learn.microsoft.com/en-us/azure/azure-functions/functions-recover-storage-account
Everything was working fine when I was using the Premium (P1v2) and the error begins when I moved to Elastic (EP1).
I am deploying it using Terraform.
Here is a TF code example we are using to deploy
locals {
app_settings = {
FUNCTIONS_WORKER_RUNTIME = "python"
FUNCTION_APP_EDIT_MODE = "readonly"
WEBSITE_VNET_ROUTE_ALL = "1"
WEBSITE_CONTENTOVERVNET = "1"
}
}
module "az_service_plan_sample" {
source = "source module"
serviceplan_name = "planname"
resource_group_name = "RG Name"
region = "East US 2"
tier = "ElasticPremium"
size = "EP1"
kind = "elastic"
capacity = 40
per_site_scaling = false
depends_on = [
module.storage_account
]
}
module "storage_account_sample" {
source = "source module"
resource_group_name = "RG Name"
location = "East US 2"
name = "saname"
storage_account_replication_type = "GRS"
subnet_ids = [subnet_ids]
}
module "sample" {
source = "source module"
azure_function_name = "functionname"
resource_group_name = "RG Name"
storage_account_name = module.storage_account.storage-account-name
storage_account_access_key = module.storage_account.storage-account-primary-key
region = "East US 2"
subnet_id = subnet_ids
app_service_id = module.az_service_plan.service_plan_id
scope_role_storage_account = module.storage_account.storage-account-id
azure_function_version = "~4"
app_settings = local.app_settings
key_vault_reference_identity_id = azurerm_user_assigned_identity.az_func.id
pre_warmed_instance_count = 2
identity_type = "UserAssigned"
user_assigned_identityies = [{
id = azurerm_user_assigned_identity.az_func.id
principal_id = azurerm_user_assigned_identity.az_func.principal_id
}]
depends_on = [
module.az_service_plan_sample,
module.storage_account_sample,
azurerm_user_assigned_identity.az_func,
]
}

Answer 1

AFAIk, There is not a one specific reason for Azure function runtime unreachable, Please check the below workaround to solve the above issue,
We have tried to create a Function app using Elastic premium plan and its working fine at our end,
Please make sure that you have configured the correct WEBSITE_CONTENTAZUREFILECONNECTIONSTRING value same as AzureWebJobsStorage then try to STOP/START the function app.
Also try to set the pre_warmed_instance_count=1 instead of 2 as mentioned in this MICROSOFT DOCUMENTATION:-
The default pre-warmed instance count is 1, and for most scenarios this value should remain as 1.
For more information please refer this ARTICLE|AZURE LESSONS-AZURE FUNCTION RUNTIME UNREACHABLE.

Answer 2

When you use a Function with Elastic Premium Plan Type that has a VNET Integration, you need to add one more property called vnet_route_all_enabled to enable route outbound from your Azure Function. Also you need to first create a file in your storage account that the name of this file will be the content of this variable WEBSITE_CONTENTSHARE in your Application Settings. Below is my code suggestion:
You can check this doc to be sure: https://learn.microsoft.com/en-us/azure/azure-functions/functions-create-vnet
Below my suggest code:
locals {
app_settings = {
FUNCTIONS_WORKER_RUNTIME = "python"
FUNCTION_APP_EDIT_MODE = "readonly"
WEBSITE_VNET_ROUTE_ALL = "1"
WEBSITE_CONTENTOVERVNET = "1"
WEBSITE_CONTENTSHARE = "file-function"
}
}
module "az_service_plan_sample" {
source = "source module"
serviceplan_name = "planname"
resource_group_name = "RG Name"
region = "East US 2"
tier = "ElasticPremium"
size = "EP1"
kind = "elastic"
capacity = 40
per_site_scaling = false
depends_on = [
module.storage_account
]
}
module "storage_account_sample" {
source = "source module"
resource_group_name = "RG Name"
location = "East US 2"
name = "saname"
storage_account_replication_type = "GRS"
subnet_ids = [subnet_ids]
}
resource "azurerm_storage_share" "share_file_ingest_function" {
name = "file-function"
storage_account_name = module.storage_account_sample.name
depends_on = [
module.storage_account_sample
]
}
module "sample" {
source = "source module"
azure_function_name = "functionname"
resource_group_name = "RG Name"
storage_account_name = module.storage_account.storage-account-name
storage_account_access_key = module.storage_account.storage-account-primary-key
region = "East US 2"
subnet_id = subnet_ids
app_service_id = module.az_service_plan.service_plan_id
scope_role_storage_account = module.storage_account.storage-account-id
azure_function_version = "~4"
app_settings = local.app_settings
key_vault_reference_identity_id = azurerm_user_assigned_identity.az_func.id
pre_warmed_instance_count = 2
vnet_route_all_enabled = true
identity_type = "UserAssigned"
user_assigned_identityies = [{
id = azurerm_user_assigned_identity.az_func.id
principal_id = azurerm_user_assigned_identity.az_func.principal_id
}]
depends_on = [
module.az_service_plan_sample,
module.storage_account_sample,
azurerm_user_assigned_identity.az_func,
]
}