define a cosmos DB connection string into an Azure function app_settings

[pchevallier]

I feel the need to document the use case where you need to link an azure function to the cosmos DB database using the connection string.

Assume you have declared a cosmosdb resource in your TF script like this

resource "azurerm_cosmosdb_account" "db" {
..
}

and now you want to define the connection string in you your azure function:

resource "azurerm_function_app" "function_name" {
  ..
  app_settings = {
     ....
     "cosmosdb_readwrite_primary_key"       = azurerm_cosmosdb_account.db.connection_strings[0],
     "cosmosdb_readwrite_secondary_key"  = azurerm_cosmosdb_account.db.connection_strings[1],
    }

So, obviously this is assuming the array respects the current following description by MSFT:
az cosmosdb keys list --type connection-strings

{
  "connectionStrings": [
    {
      "connectionString": "AccountEndpoint=https://<redacted>.documents.azure.com:443/;AccountKey=<redacted>",
      "description": "Primary SQL Connection String"
    },
    {
      "connectionString": "AccountEndpoint=https://<redacted>.documents.azure.com:443/;AccountKey=<redacted>",
      "description": "Secondary SQL Connection String"
    },
    {
      "connectionString": "AccountEndpoint=https://<redacted>.documents.azure.com:443/;AccountKey=<redacted>",
      "description": "Primary Read-Only SQL Connection String"
    },
    {
      "connectionString": "AccountEndpoint=https://<redacted>.documents.azure.com:443/;AccountKey=<redacted>",
      "description": "Secondary Read-Only SQL Connection String"
    }
  ]
}

[sinbai]

@pchevallier thank you for opeing this issue. Per the description "A map of key-value pairs for App Settings and custom values." of app_settings in the terraform doc, I assume that your use case would like to define a map of key-value pairs for custom values about cosmos db connection string in app_settings property, right? If so, I don't think it is necessary to document a sample in terraform doc, as the key-value pairs could be any strings you would like to define. what do you think?

[pchevallier]

@sinbai thank you for the follow up.
A generic solution could perhaps consists of referencing the type of connection string we want to use directly in the TF cosmosdb model.
Example:

app_settings = {
     ....
     "ex_cosmosdb_primary_key"     =  azurerm_cosmosdb_account.db.connection_strings.primary_key,
     "ex_cosmosdb_secondary_key"   = azurerm_cosmosdb_account.db.connection_strings.secondary_key

That would avoid any future inconsistency if the structure of the array were to be changed by MSFT.

[github-actions]

This functionality has been released in v3.28.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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[github-actions]

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