Unexpected costs in Azure Function & Storage

Question

Now, I'm using Azure Functions & Azure Storage. Recently, while checking the cost of resources, I found out that there was an unexpected cost in Storage. The following image shows the cost list for the storage account. (Units: Japanese yen.) You can see that the write operation of file sharing incurs a cost.

Checking the metrics of File sharing, we see that a transaction has occurred.

However, since there is no access to File sharing in the code, and the function is executed only a few times a day, I don't know why this transaction is occurring. Does anyone know of a way to mitigate this cost?

The following is an summary of Fucntions.

• Runtime: Node 14
• Function extension version: 3
• Number of functions:
  • HTTP trigger: 6 (Executes about 3 times a day.)
  • Time trigger: 1 (Every four hours.)
• Plan: pay-as-you-go

host.json:

{
  "version": "2.0",
  "logging": {
    "fileLoggingMode": "never",
    "logLevel": {
      "default": "None"
    },
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[1.*, 2.0.0)"
  }
}

I referred to the related article, but could not solve the problem.

• https://github.com/Azure/Azure-Functions/issues/832
• https://github.com/Azure/Azure-Functions/issues/1307
• Expensive use of storage account from Azure Functions

Answer 1

Azure functions use Azure Storage to manage keys/run state/store code. This is outlined here: Storage Considerations

This is likely the cost associated with these operations which can not be mitigated.