Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/vm/vminsights-configure-workspace
https://docs.microsoft.com/en-us/azure/azure-monitor/app/create-workspace-resource

Azure Functions offers built-in integration with Azure Application Insights to monitor functions.
The following areas of Application Insights can be helpful when evaluating the behavior, performance, and errors in your functions:
Live Metrics: View metrics data as it's created in near real-time.
Failures
Performance
Metrics
Reference:
https://docs.microsoft.com/en-us/azure/azure-functions/functions-monitoring
Topic 4, Proseware, Inc
Requirements
Policy service
You develop and deploy a stateful ASP.NET Core 2.1 web application named Policy service to an Azure App Service Web App. The application reacts to events from Azure Event Grid and performs policy actions based on those events.
The application must include the Event Grid Event ID field in all Application Insights telemetry.
Policy service must use Application Insights to automatically scale with the number of policy actions that it is performing.
Policies
Log policy
All Azure App Service Web Apps must write logs to Azure Blob storage. All log files should be saved to a container named logdrop. Logs must remain in the container for 15 days.
Authentication events
Authentication events are used to monitor users signing in and signing out. All authentication events must be processed by Policy service. Sign outs must be processed as quickly as possible.
PolicyLib
You have a shared library named PolicyLib that contains functionality common to all ASP.NET Core web services and applications. The PolicyLib library must:
Exclude non-user actions from Application Insights telemetry.
Provide methods that allow a web service to scale itself.
Ensure that scaling actions do not disrupt application usage.
Other
Anomaly detection service
You have an anomaly detection service that analyzes log information for anomalies. It is implemented as an Azure Machine Learning model. The model is deployed as a web service. If an anomaly is detected, an Azure Function that emails administrators is called by using an HTTP WebHook.
Health monitoring
All web applications and services have health monitoring at the /health service endpoint.
Issues
Policy loss
When you deploy Policy service, policies may not be applied if they were in the process of being applied during the deployment.
Performance issue
When under heavy load, the anomaly detection service undergoes slowdowns and rejects connections.
Notification latency
Users report that anomaly detection emails can sometimes arrive several minutes after an anomaly is detected.
App code
EventGridController.cs
Relevant portions of the app files are shown below. Line numbers are included for reference only and include a two-character prefix that denotes the specific file to which they belong.

LoginEvent.cs
Relevant portions of the app files are shown below. Line numbers are included for reference only and include a two-character prefix that denotes the specific file to which they belong.

Graphical user interface Description automatically generated

Box 1: DynamicThresholdCriterion
Box 2: Http5xx
Server errors are in the 5xx range.
Client errors are in the 4xx range
Box 3: Low
Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/alerts/alerts-dynamic-thresholds

Explanation
Using topic client, call RegisterMessageHandler which is used to receive messages continuously from the entity. It registers a message handler and begins a new thread to receive messages. This handler is waited on every time a new message is received by the receiver.
subscriptionClient.RegisterMessageHandler(ReceiveMessagesAsync, messageHandlerOptions); Reference:
https://www.c-sharpcorner.com/article/azure-service-bus-topic-and-subscription-pub-sub/

Explanation: