How to ensure only one Azure Function BlobTrigger runs at a time?

Question

I have a use case to implement multiple BlobTriggers in Azure Functions (using the Linux Consumption Plan). For example in Azure Storage I would have 5 different clients with a directory structure like:

client1/file.txt
client2.file.txt
client3/file.txt
client4/file.txt
client5/file.txt

It's possible for both client1/file.txt and client2/file.txt to be dropped off at the same time in Azure Storage. To prevent race conditions and exceeding the 1.5 GB memory limit, I would like the BlobTrigger for client1/file.txt to wait for the BlobTrigger for client2/file.txt to finish or vice versa (the order doesn't matter here, just that both of them eventually execute).

Do I have to set up a queue process separately? Can I use the preview setting WEBSITE_MAX_DYNAMIC_APPLICATION_SCALE_OUT to achieve this easily?

Would using durable functions be a better/more reliable solution?

Answer 1

Hi @TomTakiyama-3838

Blob trigger uses Queue storage under the covers, so in order to process your blobs one-by-one, you'll want to set batchSize setting to 1 (default is 16) in your host.json file:

{  
    "version": "2.0",  
    "extensions": {  
        "queues": {  
            ...  
            "batchSize": 1  
            ...  
        }  
    }  
}