Skip to main content
Welcome to this comprehensive guide on troubleshooting application failures. In this article, we review systematic troubleshooting techniques and provide practical scenarios to help you diagnose and resolve issues in a two-tier application architecture.

​
Overview

Consider a two-tier application consisting of a web server and a database server. The database pod hosts a database application and serves data to the web servers via a database service. Meanwhile, the web server, running on a separate pod, delivers content to the users through a web service.
Before you begin troubleshooting, document your application’s configuration by creating a system map or listing all components and their connections. This documentation can be a valuable reference when determining where to start your investigation.

​
Troubleshooting the Web Application

When users report issues accessing your application, start by testing the application’s front end. For example, if your application is web-based, verify the accessibility of the web server using a tool like curl on the service’s IP address and node port:

​
Validate Service Endpoints

Ensure that the web service has correctly discovered endpoints for the web pod. A common issue is a mismatch between the selectors defined on the service and those on the pod. View the service details with:
You should see output similar to the following:

​
Verify Pod Configuration

Review the web application’s pod definition to ensure it is correctly configured and running:
Next, check the pod status. A stable pod typically shows a running status with minimal restarts:
Example output:
For a more detailed inspection, including event logs, use:
This command may display events like:

​
Review Application Logs

Examine the application logs with:
Expected output might look like this:
If these logs do not shed light on a recent failure, continuously stream the logs to capture real-time activity:

​
Troubleshooting the Database Service

Apply a similar approach to verify the status of the database (DB) service. Examine the following:
  • Inspect the DB service details.
  • Confirm that endpoints are configured correctly.
  • Check the DB pod’s status.
  • Review the database logs for errors that might signal issues within the database.
Ensure that both the web and DB services have matching selectors for their respective pods. Mismatches in labels can lead to missing endpoints and connectivity issues.

​
Visualizing the Dependency Chain

The diagram below illustrates the troubleshooting flow for dependent applications. It outlines the sequence from the database (DB) to the web service (WEB-Service), including both the DB-Service and WEB components:
The image illustrates a flowchart titled "Check Dependent Applications," showing a sequence from DB to WEB-Service, involving DB-Service and WEB components.

​
Additional Resources

For further troubleshooting guidance and best practices, refer to the following resources:

​
Final Tip

Use the command below to obtain detailed information about any pod. Replace $ with the actual pod name.
By following these steps, you can effectively troubleshoot and resolve application failures in your Kubernetes environment while ensuring a systematic approach that covers both the service and pod components.

Watch Video

Practice Lab