What Azure Application Insights Actually Tracks (and Why You'd Turn It On)
A quick look at what this tool watches, and when you actually need it
By Shehryar Hassan, Microsoft 365 & Azure Consultant
Someone asked me last week why their App Service kept timing out and nobody could tell them which page was slow. Turns out nobody had turned on Application Insights. That's usually the story. It's not obscure, it's just easy to skip when you're setting up a web app in a hurry.
What it actually watches
Application Insights is Azure's monitoring tool for apps, not infrastructure. Where Azure Monitor watches VMs and resource health, Application Insights watches what happens inside your code while it runs. It tracks:
- How long each request takes to respond
- Which dependencies (databases, APIs, storage) are slow or failing
- Exceptions and stack traces as they happen, not after someone reports a bug
- How many users are actually hitting each page
- Custom events you add yourself, if you want to track something specific
You turn it on per app, not per subscription. On App Service it's a checkbox during setup, or you can add it later from the app's Monitoring section. For anything else, function apps, containers, VMs, you install a small SDK or agent that sends the data to a Log Analytics workspace behind the scenes.
When it's worth turning on
If you're running one small internal app with five users, you probably don't need it. The value shows up once something goes wrong at 2am and you'd rather look at a chart than SSH into a server. It's also useful before something goes wrong, the Live Metrics view shows requests and failures as they happen, which is handy right after a deployment.
The one thing to watch is cost. Application Insights charges by data volume ingested, and a busy app can log a lot more than you expect, especially with verbose logging turned on everywhere. Set a daily cap in the workspace settings so a bad day doesn't turn into a bad bill. Most teams find the default sampling rate is fine, it keeps a representative slice of the data instead of logging every single request.
If you already pay for App Service or Azure Functions, turning on Application Insights costs you a checkbox and maybe a few dollars a month. It's one of the few Azure features that pays for itself the first time you use it to find a real problem.
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