[BUG] BlobBaseClient.Exists always logs exceptions to App Insights when the blob does not exist.

[mrpmorris]

Describe the bug
BlobBaseClient.Exists files lots of false exceptions in App Insights when the blob does not exist.

Expected behavior
Checking if a blob exists should simply return false, not log an exception in App Insights.

Actual behavior (include Exception or Stack Trace)
App Insights is littered with false-positive exceptions due to a 404 response code to a HEAD request.

To Reproduce
Steps to reproduce the behavior (include a code snippet, screenshot, or any additional information that might help us reproduce the issue)

1. Create an app that connects to a valid blob storage
2. Enable AppInsights
3. Access BlobBaseClient.Exists for a blob you know does not exist
4. Look in AppInsights

Environment:

• Name and version of the Library package used: Azure.Storage.Blobs 12.4.4
• Hosting platform or OS and .NET runtime version: Azure Function app (net core 3.1)

The problem seems to be here

azure-sdk-for-net/sdk/storage/Azure.Storage.Queues/src/Generated/ServiceRestClient.cs

Line 162 in f01cbdc

throw await _clientDiagnostics.CreateRequestFailedExceptionAsync(message.Response).ConfigureAwait(false);

The code throws an exception for anything other than a 200 response - but 404 is not an exceptional response, it is very much expected - in fact, I expect to call it for non-existent blobs more often than any other blob scenario.

Ultimately, the exception is swallowed here
https://github.com/Azure/azure-sdk-for-net/blob/master/sdk/storage/Azure.Storage.Blobs/src/BlobBaseClient.cs#L2952

But, by this point in time, the exception has already been logged to App Insights.

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @xgithubtriage.

Issue Details

---

Describe the bug
BlobBaseClient.Exists files lots of false exceptions in App Insights when the blob does not exist.

Expected behavior
Checking if a blob exists should simply return false, not log an exception in App Insights.

Actual behavior (include Exception or Stack Trace)
App Insights is littered with false-positive exceptions due to a 404 response code to a HEAD request.

To Reproduce
Steps to reproduce the behavior (include a code snippet, screenshot, or any additional information that might help us reproduce the issue)

1. Create an app that connects to a valid blob storage
2. Enable AppInsights
3. Access BlobBaseClient.Exists for a blob you know does not exist
4. Look in AppInsights

Environment:

• Name and version of the Library package used: Azure.Storage.Blobs 12.4.4
• Hosting platform or OS and .NET runtime version: Azure Function app (net core 3.1)

The problem seems to be here

azure-sdk-for-net/sdk/storage/Azure.Storage.Queues/src/Generated/ServiceRestClient.cs

Line 162 in f01cbdc

throw await _clientDiagnostics.CreateRequestFailedExceptionAsync(message.Response).ConfigureAwait(false);

The code throws an exception for anything other than a 200 response - but 404 is not an exceptional response, it is very much expected - in fact, I expect to call it for non-existent blobs more often than any other blob scenario.

Ultimately, the exception is swallowed here
https://github.com/Azure/azure-sdk-for-net/blob/master/sdk/storage/Azure.Storage.Blobs/src/BlobBaseClient.cs#L2952

But, by this point in time, the exception has already been logged to App Insights.

Author:	mrpmorris
Assignees:	-
Labels:	Client, Service Attention, Storage, customer-reported, needs-team-attention, needs-triage, question
Milestone:	-

[jsquire]

//cc: @tg-msft, as he was involved in an earlier discussion on this topic.

[jsquire]

Thank you for your feedback. Tagging and routing to the team best able to assist.

[tg-msft]

This is waiting on #9934.

[janid1967]

I am experiencing the same problem and looking forward to a fix of this

[seanmcc-msft]

@tg-msft, what is the status of #9934 ?

[tg-msft]

Last I heard, we're still officially waiting for an answer from the Observability folks. +@pakrym who recently removed some noise for CreateIfNotExists calls and can comment further. I don't think his recent change would help with BlobBaseClient.Exists though because we don't add any conditional headers to the request.

[pakrym]

We haven't gotten clear guidance but I think we can still make progress on our own. We are going to start with fixing the CreateIfNotExists and then look into adding support to pass ResponseClassifier to the code-generated methods. That way we can create and pass custom classifiers to calls that return expected 404s.

[amnguye]

@tg-msft @pakrym was there an update on #9934 yet ?
Also did CreateIfNotExists get fixed in regards to this issue?

[bruckGT1]

I am also seeing this behavior. Any updates?

[amishra-dev]

@pakrym Pavel will we be accepting the fix for #9934?

[tg-msft]

We don't want the fix at #9934 - we want to enable this via the work being done as part of #25626 that will be the standard pattern across the Azure SDK for .NET.

[amishra-dev]

@tg-msft Ted any update on this? @jaschrep-msft can you please track this from our side?

[tg-msft]

Yes, the basic Azure.Core features are now in (but not shipped yet) and the generator has been updated to produce LLC protocol methods with a flag. That means you could start enabling this with a package reference, though it won't fully light up until a fix for Azure/autorest.csharp#2006 is committed and deployed.

[older]

@tg-msft It looks like that AutoRest issue was fixed in March. Is this one going to be fixed as well?

[annelo-msft]

The required APIs should be available now in Azure.Core to be able to implement this feature. In order to suppress distributed tracing for a given status code, AddClassifier() should be called on RequestContext prior to passing it to the method in question. An example can be found in the TableServiceClient here.

Please reach out with any remaining questions on implementation.