Azure Function Cannot Find host.json

Question

I am attempting to deploy an Azure Function in Terraform that must retrieve database connection strings from Azure Key Vault and then pass them to a python application deployed on a container instance. However despite several restructuring attempts, it cannot seem to find the host.json file.

The image queries a public API and then calls this function to write the API GET results to a postgres database.

The current file layout is:

- azure_function_secrets
  - main.tf
  - variable.tf
  - src
    - host.json
    - requirements.txt
    - azure_func
      - azure_func.py
      - function.json

The resource code in main.tf is defined as:

# Specify where terraform can locate the compressed function app logic and files
data "archive_file" "functionapp_zip" {
  type        = "zip"
  source_dir  = "./modules/azure_function_secrets/src"  # Point to the src directory
  output_path = "./modules/azure_function_secrets/functionapp.zip"
}

resource "azurerm_app_service_plan" "func_secrets_sp" {
  name                = "az-func-secrets-sp"
  resource_group_name      = data.azurerm_resource_group.resource_group.name
  location                 = data.azurerm_resource_group.resource_group.location
  kind                = "FunctionApp"
  sku {
    tier = "Dynamic"
    size = "Y1"
  }
}

resource "azurerm_function_app" "secrets_function" {
  name                       = "secrets-function"
  resource_group_name        = data.azurerm_resource_group.arc_resource_group.name
  location                   = data.azurerm_resource_group.resource_group.location
  app_service_plan_id        = azurerm_app_service_plan.func_secrets_sp.id
  storage_account_name       = var.storage_account_name
  storage_account_access_key = var.storage_account_access_key

  app_settings = {
    "FUNCTIONS_WORKER_RUNTIME" = "python"
    "WEBSITE_RUN_FROM_PACKAGE" = azurerm_storage_blob.functionapp_secrets_code.url
    TF_VAR_SUBSCRIPTION_ID = var.subscription_id
    TF_VAR_RESOURCE_GROUP_NAME = data.azurerm_resource_group.resource_group.name
    TF_VAR_LOCATION = data.azurerm_resource_group.resource_group.location
  }

  site_config {
    always_on                = false
    ftps_state               = "Disabled"
    use_32_bit_worker_process = false
  }

  identity {
    type = "SystemAssigned"
  }
}

The host.json file is defined as:

{
    "version": "2.0",
    "logging": {
      "logLevel": {
        "default": "Debug"
      },
      "applicationInsights": {
        "samplingSettings": {
          "isEnabled": true,
          "excludedTypes": "Request"
        }
      }
    }
  }
  

The function itself is:

def main(req: func.HttpRequest) -> func.HttpResponse:
    logging.info('Python secret retrieval function triggered.')

    # Setup Key Vault client
    try:
        credential = DefaultAzureCredential()
        key_vault_url = "https://<vault_name>.vault.azure.net/"
        secret_client = SecretClient(vault_url=key_vault_url, credential=credential)

        # Fetch secrets
        user = secret_client.get_secret('username').value
        password = secret_client.get_secret('password').value


        return func.HttpResponse(
            body = f'{{"user": "{user}", "password": "{password}"}}',
            mimetype="application/json"
        )

However, I consistently find this error in the AZ Function user interface on deployment:

 mscorlib: Could not find file 'C:\home\site\wwwroot\host.json

Investigation into the container logs shows that the image is deployed without issue but the function is not:

Function host is not running.

I have tried moving the host.json file to the root and function directories without success. I have confirmed that the RBAC controls around the function are correct and should grant access. I have deployed monitoring insights but the log stream did not give any new errors to identify the issue.

Answer 1

Azure Function Cannot Find host.json: -

First of all, double-check the path of the src directory specified in the data "archive_file" "functionapp_zip" block.

And if the path is accurate but it still does not work, it indicates that it cannot always find the root directory automatically. In that instance, set up a root directory path within the appsettings block in the function_app resource using AzureWebJobsScriptRoot as detailed in the doc.

After checking all, I modified the required part of your code as shown below while keeping the rest of the code same.

resource "azurerm_app_service_plan" "func_secrets_sp" {
  name                = "xxxxx"
  resource_group_name      = data.azurerm_resource_group.resource_group.name
  location                 = data.azurerm_resource_group.resource_group.location
  kind                = "FunctionApp"
  sku {
    tier = "Dynamic"
    size = "Y1"
  }
}
resource "azurerm_function_app" "secrets_function" {
  name                       = "xxxxxx"
  resource_group_name        = data.azurerm_resource_group.arc_resource_group.name
  location                   = data.azurerm_resource_group.resource_group.location
  app_service_plan_id        = azurerm_app_service_plan.func_secrets_sp.id
  storage_account_name       = var.storage_account_name
  storage_account_access_key = var.storage_account_access_key

  app_settings = {
    "FUNCTIONS_WORKER_RUNTIME" = "python"
    "WEBSITE_RUN_FROM_PACKAGE" = azurerm_storage_blob.functionapp_secrets_code.url
    "AzureWebJobsScriptRoot" = "Set the root path as per your need"
    TF_VAR_SUBSCRIPTION_ID = var.subscription_id
    TF_VAR_RESOURCE_GROUP_NAME = data.azurerm_resource_group.resource_group.name
    TF_VAR_LOCATION = data.azurerm_resource_group.resource_group.location
  }

  site_config {
    always_on                = false
    ftps_state               = "Disabled"
    use_32_bit_worker_process = false
  }

  identity {
    type = "SystemAssigned"
  }
}

Deployment succeeded: