In general, HTTP 4xx responses indicate client issues. However, when creating a distributed web service with Azure App Services, some number of 4xx responses are expected. Blue Matador watches the Http4xx metric for the number of 4xx responses returned by your app service, and creates events when this metric is anomalous. A sudden spike in the number of 4xx responses can be the result of the following:
HTTP 4xx responses usually result from problems specific to your application, but the general process for troubleshooting the problem is the same for most applications. First, enable and check access logs for your app service. Look for the endpoint or endpoints that are returning the 4xx status codes. Next, scan the logs emitted by that endpoint (with the log management solution your organization uses) for exceptions or other errors that could be resulting in 4xx responses. Finally, fix the issue and deploy the solution.