The reason to remove 500 HTTP error codes is to reduce overall number of 500s so that we can do better monitoring for other errors, which would otherwise be masked by large number of 'build number conflict' errors.

Please return a 409 Conflict in this case. Clients shouldn't retry 4xx errors and it will let is still track the rate of these errors in graphs (vs everything looking like a 200 success).

Ack. Also I've noticed that those errors do not necessarily happen when uploading incremental_results.json. They also happen when uploading full_results.json. It could be even that they only come from full_results.json.

Cofirmed - they only happen on full_results.json since the following query returns no results in the last 2 days: https://pantheon.corp.google.com/logs/viewer?project=test-results-hrd&key1=go&minLogLevel=0&expandAll=false&resource=appengine.googleapis.com&logName=projects%2Ftest-results-hrd%2Flogs%2Fappengine.googleapis.com%252Frequest_log&advancedFilter=metadata.serviceName%3D%22appengine.googleapis.com%22%0Alog%3D%22appengine.googleapis.com%2Frequest_log%22%0A%22build%20number%20conflict%22%0A-%22updateFullResults%22%0A.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra.git/+/bb281b54acb9d6af56ff0c1696b32fe3b4f201bc

commit bb281b54acb9d6af56ff0c1696b32fe3b4f201bc
Author: sergiyb <sergiyb@chromium.org>
Date: Thu Sep 22 00:29:30 2016

Return 409 error when uploading build with same number again

R=estaab@chromium.org
BUG= 648716 

Review-Url: https://codereview.chromium.org/2355353002

[modify] https://crrev.com/bb281b54acb9d6af56ff0c1696b32fe3b4f201bc/go/src/infra/appengine/test-results/frontend/upload.go
[modify] https://crrev.com/bb281b54acb9d6af56ff0c1696b32fe3b4f201bc/go/src/infra/appengine/test-results/frontend/upload_test.go