5.1.3.1. Troubleshoot Azure App Service

First Principle: Troubleshooting Azure App Service focuses on diagnosing and resolving application errors, performance degradation, and availability issues. Its core purpose is to minimize downtime and restore application health through a systematic workflow and leveraging built-in diagnostic tools.

What It Is: Azure App Service applications may face issues such as HTTP 5xx errors (server-side failures), slow performance, deployment failures, or unexpected downtime. Effective troubleshooting relies on a structured approach and leveraging Azure’s built-in tools.

Visual: "App Service Troubleshooting Toolkit"

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Common Issues:

• "Application errors": HTTP 500/502/503 (server-side errors), code exceptions, misconfigurations (e.g., incorrect connection strings, missing environment variables).
• "Performance degradation": High latency, memory leaks, CPU/memory resource exhaustion, long-running requests.
• "Deployment failures": Incomplete deployments, configuration mismatches between slots, missing dependencies.
• "Availability problems": App not responding, frequent restarts, "instance failures".

Key Troubleshooting Tools:

• "Diagnose and solve problems": In the Azure Portal, this interactive tool guides you through common issues and suggests fixes based on telemetry collected by Azure Monitor.
• "Kudu (Advanced Tools)": Access via https://<appname>.scm.azurewebsites.net for file system browsing, process explorer, environment variables, and diagnostic dumps. This provides direct access to the "App Service" instance.
• "App Service logs": Enable and review web server logs, application logs (from your code), and failed request tracing (FREB) to capture runtime details. Logs can be streamed or downloaded and sent to Log Analytics.
• "Application Insights": For deep application performance monitoring and "distributed tracing", providing end-to-end visibility. (↳ See: 5.1.2.2).

Troubleshooting Workflow:

1. "Check app status": Review "App Service health" and recent events in the Azure Portal.
2. "Review logs": Examine application and web server logs for error patterns. Use "Log Analytics queries" for deeper analysis.
3. "Use diagnostics": Run "Diagnose and solve problems" for targeted checks based on detected symptoms.
4. "Investigate with Kudu": Inspect files, environment, and running processes directly on the instance.
5. "Scale resources": If under load, "scale up" (larger instance) or "scale out" (more instances).
6. "Redeploy or rollback": If deployment is the root cause, redeploy or revert to a previous version using "deployment slots".

Scenario: Your web application, hosted on Azure App Service, suddenly starts returning HTTP 500 errors to users. You also notice a significant increase in response times. You need to quickly identify why the application is failing and restore service.

Reflection Question: How do Azure "App Service troubleshooting tools" ("Diagnose and solve problems", "Kudu", "App Service logs", "Application Insights") collectively enable you to efficiently isolate and resolve common issues, minimizing downtime and ensuring application reliability?