Scenario: Debugging Kubernetes Network Connectivity End-to-End#

The report comes in as it always does: “my application can’t reach another service.” This is one of the most common and most frustrating categories of Kubernetes issues because the networking stack has multiple layers, and the symptom (timeout, connection refused, 502) tells you almost nothing about which layer is broken.

This scenario walks through a systematic diagnostic process, starting from the symptom and narrowing down to the root cause. Follow these steps in order. Each step either identifies the problem or eliminates a layer from the investigation.

The USE Method: A Framework for Systematic Diagnosis#

The USE method, developed by Brendan Gregg, provides a structured approach to system performance analysis. For every resource on the system – CPU, memory, disk, network – you check three things:

• Utilization: How busy is the resource? (e.g., CPU at 90%)
• Saturation: Is work queuing because the resource is overloaded? (e.g., CPU run queue length)
• Errors: Are there error events? (e.g., disk I/O errors, network packet drops)

This method prevents the common trap of randomly checking things. Instead, you systematically walk through each resource and check all three dimensions. If you find high utilization, saturation, or errors on a resource, you have found your bottleneck.