Automatic retry to CosmosDb output binding - azure

Question

I'm using an Azure function that sends an array of around 200 documents to a CosmosDB via the Output Binding. That function gets triggered about 1000 at the same time by queue messages.
In some cases I get the "Request rate is large" error and the function execution fails. The documentation says when this error occurs, I can retry the execution in some milliseconds, but I suspect the azure function runtime is doing that for me. I couldn't find any documentation explicitly saying that when the output binding throws that exception it will retry automatically (like with the .NET Linq library).
Can someone point me out to see if this is the case?

Answer 1

The Output binding uses SDK 1.13.2 which already has the retry mechanism in place.
Assuming you are using Azure Functions v1, if you are using the IAsyncCollection the Function will do an UpsertDocumentAsync for each AddAsync, if you are using a single document output, then the UpsertDocumentAsync should be happening once.
In any case, the SDK retries by default 9 times on a throttled result, after that, the exception is bubbled and you Function will error; the document should go back to the queue for retrying as per the QueueTrigger design and after a couple of iterations, it goes to the deadletter queue..
If you want more granular control of the flow, you could obtain the DocumentClient and do the UpsertDocumentAsync yourself with a try/catch, if it fails more than 9 times, you can opt to send to another Queue or retry another set of times. Something like:
using Microsoft.Azure.Documents;
using Microsoft.Azure.Documents.Client;
using Microsoft.Azure.Documents.Linq;
[FunctionName("CosmosDBSample")]
public static async Task<HttpResponseMessage> Run(
[QueueTrigger("my-queue")] MyPOCOClass myMessage,
[DocumentDB("test", "test", ConnectionStringSetting = "CosmosDB"] DocumentClient client,
TraceWriter log)
{
try
{
await client.UpsertDocumentAsync(myMessage);
}
catch(DocumentClientException ex)
{
// retry / queue somewhere else?
log.Warning($"DocumentClientException {ex.Message} in document {myMessage.Id}.");
}
}