Troubleshooting Common Azure App Service Issues

This guide provides steps and common solutions for diagnosing and resolving issues you might encounter with Azure App Service.

1. Application Not Responding or Crashing

This is a frequent issue. It could be due to various reasons, including application errors, resource exhaustion, or configuration problems.

Common Causes & Solutions:

• Application Errors:
  • Check Application Logs: Navigate to your App Service in the Azure portal. Under Monitoring, select Log stream. Look for exceptions, unhandled errors, or critical messages.
  • Enable Diagnostic Logging: Ensure detailed logging is enabled in your app's configuration. For .NET apps, this might involve web.config settings. For Node.js, ensure your framework's logging is configured.
  • Remote Debugging: If possible, attach a remote debugger to your App Service instance for real-time issue identification.
• Resource Exhaustion:
  • CPU/Memory Usage: Monitor CPU and memory usage in the Overview and Metrics sections of your App Service. If consistently high, consider scaling up your App Service plan or optimizing your application code.
  • Disk Space: Ensure your application isn't filling up the disk with temporary files or logs that aren't being cleaned up.
  • Connection Limits: Applications can sometimes exhaust available database connections or external API connection pools.
• Configuration Issues:
  • Environment Variables: Verify all necessary environment variables are correctly set in the App Service configuration.
  • Application Settings: Double-check application-specific settings like connection strings, API keys, and feature flags.

2. HTTP 5xx Errors (Server Errors)

HTTP 5xx errors indicate that the server encountered an unexpected condition that prevented it from fulfilling the request.

Common Causes & Solutions:

• Application Crashes: As described above, application errors are the most common cause of 5xx errors.
• App Service Platform Issues: Though rare, there might be underlying issues with the App Service infrastructure. Check Azure Service Health.
• Resource Limits Reached: If your App Service plan is undersized, it might struggle to handle the load, leading to errors.
• Deployment Issues: A failed or incomplete deployment can leave the application in a broken state. Try redeploying or performing a "swap" operation if using deployment slots.

3. Slow Performance

Applications that are slow to respond can frustrate users and impact business operations.

Common Causes & Solutions:

• Inefficient Code:
  • Database Queries: Optimize slow database queries. Use indexes effectively.
  • External API Calls: Cache results from frequently called, slow external APIs. Implement asynchronous calls where appropriate.
  • Resource-Intensive Operations: Identify and optimize CPU- or memory-intensive parts of your application logic.
• Insufficient Resources:
  • Scale Up: Upgrade your App Service plan to a higher tier with more CPU, memory, and network bandwidth.
  • Scale Out: Increase the number of instances if your application is CPU-bound and can handle concurrent requests effectively.
• Network Latency:
  • App Service Location: Ensure your App Service is deployed in a region geographically close to your users or dependent services.
  • Content Delivery Network (CDN): For static assets, use Azure CDN to serve content faster to users worldwide.

4. Deployment Failures

Problems during the deployment process can prevent your application from running correctly.

Common Causes & Solutions:

• Build Errors: Ensure your code compiles successfully locally before deploying. Check build logs for specific errors.
• Dependency Issues:
  • Package Management: For Node.js, ensure package.json is correct and run npm install locally. For .NET, verify project files.
  • Runtime Versions: Confirm the runtime version specified in your App Service configuration matches your application's requirements (e.g., Node.js version, .NET Framework version).
• Configuration Conflicts: Sometimes, incorrect application settings or connection strings in deployment configurations can cause failures.
• Permissions: Ensure the deployment mechanism (e.g., GitHub Actions, Azure DevOps, FTP credentials) has the necessary permissions to write to the App Service.

5. Connectivity Issues

Problems connecting to databases, external APIs, or other services.

Common Causes & Solutions:

• Firewall Rules:
  • App Service IP Addresses: If your backend services have IP restrictions, ensure the App Service outbound IP addresses are allowed.
  • Backend Service Firewalls: Check firewalls on your database servers or other services.
• Network Configuration:
  • VNet Integration: If your App Service is integrated with a Virtual Network, ensure routes and network security groups are configured correctly.
  • Private Endpoints: Verify that private endpoints are set up and accessible.
• DNS Resolution: Ensure your application can resolve the hostnames of the services it needs to connect to.

6. Using the "Diagnose and solve problems" Blade

The Azure portal's built-in diagnostics tool is an invaluable resource for identifying and solving common issues quickly.

Navigate to your App Service in the Azure portal and select Diagnose and solve problems. This blade offers automated checks for:

• Availability and Performance
• Application Crashes
• Configuration Errors
• Networking Issues
• Deployment Problems
• And much more...

It often provides direct links to relevant logs, metrics, and configuration settings to help you pinpoint the root cause.