Error handling for input/output bindings

[mathewc]

We need a way for people to write error handling code for their input/output bindings, for errors that happen outside of their function logic (e.g. when binding fails in our fx code, not user code). Traditionally, our answer to this has been to rely on the inherent trigger restart logic (varies per trigger). E.g. for a queue trigger, if any of the in/out bindings fail, the queue message will be retried after some time.

However, in some cases, users want to be able to write error handling code for their bindings. They can usually do this by binding to an IAsyncCollector/ICollector and wrapping a try/catch around the calls to Add/Flush. However the model isn't consistent across all bindings. Note: we also want a solution that can apply for languages other than C# in Azure Functions scenarios.

Likely related to the Filters feature we've discussed: Azure/azure-webjobs-sdk#980. The reason being, that in order to be able to capture errors in input bindings as well, the error handling needs to be set up before the function is invoked. Initially for handling output binding scenarios, I had considered an model where the user could subscribe an event handler imperatively in their code, e.g. executionContext.OnError += .... Again - we'll need a design that works for Azure Functions non C# languages as well.

[mathewc]

The Invocation Filters feature in core SDK is now checked in, so for C# functions you can add an exception filter to address this issue.

Filter support for other languages is still pending - see #1761.

[deshmanedarshan]

Hi @mathewc, request you to comment on https://stackoverflow.com/questions/55861426/error-handling-in-azure-function-when-used-with-sendgrid-as-output-binding/55862337 this please.

[deshmanedarshan]

Hi @mathewc, Can you please let me know whether AZURE infrastructure does a retry when there is SendGrid binding failure ?

[mathewc]

The SendGrid output binding doesn't do retries itself (code https://github.com/Azure/azure-webjobs-sdk-extensions/blob/7fcca7f5ce44c28b1bc9cff51592737c95c78c5f/src/WebJobs.Extensions.SendGrid/Bindings/SendGridMessageAsyncCollector.cs#L56). It just uses the SendGrid SDK to send. If the invocation fails, retries for the trigger that caused the invocation will happen, based on what trigger type is used. E.g. if its a queue message, the queue message will be retried after some time.