Troubleshooting Azure App Service

Application Not Responding (5xx Errors)

When your application returns a 5xx server error, it indicates a problem on the server-side. Here's how to investigate:

• Check Application Logs: Use the Kudu console or Azure Monitor to access application logs for detailed error messages. Look for unhandled exceptions, memory leaks, or configuration errors.
• Review Deployment History: If the issue started after a recent deployment, consider rolling back to a previous stable version.
• Resource Utilization: High CPU, memory, or disk usage can lead to application instability. Monitor your App Service plan's metrics.
• Configuration Settings: Ensure application settings, connection strings, and environment variables are correctly configured.

Common Pitfalls:

• Incorrect database connection strings.
• Missing required assemblies or dependencies.
• Infinite loops or deadlocks in application code.

Application Offline or Unreachable (4xx Errors, Timeout)

These errors usually point to issues with application availability, networking, or client-side problems.

• App Service Status: Verify the status of your App Service in the Azure portal. Ensure it's running.
• Networking Issues: Check network security groups, firewalls, and DNS settings if you're experiencing connectivity problems.
• Application Pool Recycling: Sometimes, the application pool might recycle unexpectedly. Check event logs for reasons.
• Deployment Slots: If using deployment slots, ensure the correct slot is currently the production slot.

Performance Degradation

Slow application response times can be frustrating. Identify bottlenecks with these steps:

• Performance Monitoring: Utilize Azure Application Insights for detailed performance metrics, request traces, and dependency mapping.
• Database Performance: Slow database queries are a common cause. Analyze query execution plans and optimize them.
• Caching Strategies: Implement effective caching mechanisms to reduce load on your backend services.
• Scaling: If your application is experiencing high traffic, consider scaling up your App Service plan or scaling out instances.

Example: Diagnosing slow requests with Application Insights:

-- Query to find slowest requests in the last hour
requests
| order by duration desc
| take 10
                

Deployment Failures

Problems during deployment can prevent your application from going live.

• Deployment Logs: Always review the detailed logs provided by your deployment method (e.g., Kudu, GitHub Actions, Azure DevOps).
• Build Failures: If deploying from source code, ensure your build process completes successfully and all dependencies are met.
• Permissions: Verify that the service principal or user account used for deployment has the necessary permissions to access the App Service.
• Deployment Method Specifics: Refer to the documentation for your specific deployment tool for common issues.

Security and Authentication Issues

Ensuring your application is secure is paramount.

• SSL Certificates: Ensure your SSL certificates are valid and correctly configured.
• Authentication Providers: If using Azure AD or other identity providers, verify their configurations and token issuance.
• Access Restrictions: Review IP restrictions and service endpoint configurations.
• Vulnerability Scanning: Regularly scan your application for potential security vulnerabilities.