Azure Function cosmosDB trigger managed identity not working

Question

I created an isolated Azure functions for cosmosDB trigger. I'm using Microsoft.Azure.Functions.Worker.Extensions.CosmosDB --version 4.0.0-preview2 to use managed identity. Below is my function.

[Function("CosmosDBTrigger")]
    public void Run([CosmosDBTrigger(
        databaseName: "testdata",
        containerName: "test",
        Connection = "connect",
        LeaseContainerName = "leases")] IReadOnlyList<MyDocument> input)
    {}

local.settings.json

{
  "Values": {
   connect__accountEndpoint": "https://testdatacosmosdb.documents.azure.com:443/"
}}

I get the error "Cosmos DB connection configuration 'connect' does not exist. Make sure that it is a defined App Setting. I'm not sure if it happening because of isolated azure functions

Answer 1

You are missing the credentials. See:

• https://learn.microsoft.com/azure/azure-functions/functions-reference?tabs=cosmos#common-properties-for-identity-based-connections
• https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-cosmosdb-v2-trigger?tabs=in-process%2Cfunctionsv2&pivots=programming-language-csharp#identity-based-connections

All Azure Functions bindings that are going to use MSI need the <your attribute value>__credential in the configuration besides the Service Specific properties.

For Cosmos DB, the Service Specific property is accountEndpoint.

To summarize, you need to have both.

In your local.settings.json file:

{
   "connect" : {
      "accountEndpoint": "https://testdatacosmosdb.documents.azure.com:443/",
      "credential" : "managedidentity"

    }
}

Once deployed in Azure, you need to add them to your Functions App Configuration, for that you can use the underscore notation:

The version you are using of the package is old and only supports adding these on the "Connection Strings" section of the Function App Configuration.

"connect__accountEndpoint": "https://testdatacosmosdb.documents.azure.com:443/"

"connect__credential": "managedidentity"

Here is also an Azure Friday episode of the whole scenario end to end: https://www.youtube.com/watch?v=w002dYaP9mw