Instrumenting an app for monitoring
1. Instrumenting an app for monitoring
Welcome back! In the last chapter we covered Application Insights, availability tests and log analytics, let's now explore app instrumentation.2. Instrumentation vs application insights
Instrumentation is the act of enabling telemetry in your app. Application Insights is the Azure service that collects and analyzes that telemetry.3. Instrumenting an app for monitoring
Running an app without monitoring is like driving at night with the headlights off. You know you’re moving, but you have no idea what’s happening ahead.4. Instrumentation
Azure cannot magically understand what your application is doing. To collect meaningful data—like requests, failures, and performance, you need to instrument your app. Instrumentation is what turns an app into something observable.5. What is app instrumentation?
App instrumentation means adding monitoring capabilities to your application so it can emit telemetry. This includes request rates, response times, errors, and dependencies. Once instrumented, your app actively reports what it’s doing to Azure monitor instead of staying silent.6. Auto-instrumentation
The easiest way to get started is auto-instrumentation. Azure can automatically instrument many services, such as App Services and Azure Functions without you writing any monitoring code. Flip it on, and telemetry starts flowing.7. Auto-instrumentation in action
When you enable Application Insights on an App Service, Azure injects the required monitoring behind the scenes. Your app immediately starts sending requests and performance data with no redeployment required.8. What Azure injects automatically
When auto-instrumentation is enabled, Azure injects an Application Insights agent into the runtime environment. The agent uses runtime-level SDK hooks to read application activity and emit telemetry automatically, without requiring explicit SDK references or code changes in the application.9. The silent failure
A team deploys their API to production. Everything seems fine until a partner company complains their integration stopped working three days ago. Server metrics show nothing: CPU normal, memory normal, no crashes.10. The silent failure
Without instrumentation, they have no visibility into error rates or which endpoints failed. They spend two days adding logging, redeploying, and reproducing the issue. With instrumentation enabled from the start, they would have seen the failure immediately: a specific endpoint returning 500 errors since a dependency URL changed. This means it took ten minutes to diagnose instead of two days.11. Manual instrumentation
Manual instrumentation means adding an Application Insights SDK to your code. This gives you more control, letting you track custom events, business metrics, or detailed traces.12. Keys and connections
To send telemetry, your app needs to know where to send it. This is defined by the Application Insights connection string, which specifies the destination for all monitoring data. When you use auto-instrumentation, Azure configures this connection automatically for you. However, when you manually instrument an application using an SDK, you must explicitly provide the connection string, otherwise no telemetry is collected or sent to Azure Monitor.13. Environment variables
Under the hood, Azure sets the Application Insights connection string as an environment variable. The monitoring agent reads this value at runtime.14. Troubleshooting
If telemetry is missing, start by checking whether auto-instrumentation is enabled, the connection string is present, and the platform supports it. Conflicts can occur if manual SDK configuration overrides platform settings.15. Summary
In this lesson, you learned how auto-instrumentation enables applications to produce telemetry without modifying code. Azure injects monitoring at the platform and runtime level, automatically sending data to Azure Monitor. This approach provides fast, consistent visibility into your applications and forms the foundation for deeper monitoring, diagnostics, and troubleshooting.16. Let's practice!
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