Sherlock Holmes and The Case of the Cloudflare Timeout Mystery

Welcome to our Sherlock Holmes-inspired tech adventure Series! Imagine each technical challenge as a thrilling mystery waiting to be solved. Like Sherlock Holmes with his sharp eye for detail, I'll tackle the problem with wit and precision. Let's dive in and crack these cases together!

The Case: Cloudflare Gateway Timeout Errors

We recently embarked on a journey to migrate our application to Kubernetes. The migration process went smoothly, and we successfully moved the majority of our main application. However, shortly after, our clients started experiencing issues. They reported seeing Cloudflare's Gateway Timeout error, though the issue seemed to resolve itself upon refreshing.

Initial Investigation

Given that the error message indicated a timeout, it was clear that our application was not responding within the specified time limit. We started our investigation:

1. Server Logs Review: We reviewed the server logs but found no obvious issues. Everything seemed to be running fine, and we couldn't pinpoint the exact times when users were facing problems due to the randomness of the complaints.

2. Correlated with Migration: One clear observation was that these issues began occurring right after our migration to Kubernetes. This led us to believe that something related to the Kubernetes setup might be causing the problem.

Discovery and Analysis

The breakthrough came when one of our colleagues encountered the same error. We checked the server logs again, and while they appeared normal, a deeper analysis revealed a critical insight:

• We had recently pushed code to our live server, which triggered a server restart (or, more specifically, a pod restart in Kubernetes).

• To confirm if the restart was the issue, we manually restarted the pod and observed that the error could be reproduced until the server was fully up and running.

Root Cause: Cold Start Time

Our initial assumption was that Kubernetes would handle the transition smoothly, keeping the old server down only once the new server was up and running. While Kubernetes does handle this, we overlooked one crucial detail: cold start time.

Cold start time refers to the period required for a new container to start up, connect to the database, and be fully operational. During this time, Kubernetes might route requests to the new container before it's ready, leading to failures and timeouts.

The Solution: Kubernetes Probes

To address the issue, we delved into Kubernetes features and discovered the concept of Probes. Probes are essential for managing the state of containers and ensuring that they are ready to handle traffic. Kubernetes offers three types of probes:

1. Liveness Probe: This probe indicates whether a container is still running. If the probe fails, Kubernetes will kill and restart the container. It helps catch issues like deadlocks and improves application availability.

2. Readiness Probe: This probe checks whether the application in the container is ready to accept requests. If the probe fails, Kubernetes will remove the pod from the service's endpoints, preventing traffic from being sent to it. This probe is crucial for handling the cold start issue because it ensures that requests are only sent to containers that are fully up and running.

   Note: If you don't set a readiness probe, Kubernetes assumes that the application is ready to handle traffic as soon as the container starts. This can lead to request failures during the container's startup period.

3. Startup Probe: This probe determines whether the application has started. Once the startup probe succeeds, other probes begin to function. If the probe fails, Kubernetes will restart the container.

Implementing the Solution

To resolve our issue, we implemented the Readiness Probe in our Kubernetes configuration. This adjustment ensured that traffic was only directed to containers that were fully operational, thus eliminating the Gateway Timeout errors our clients were experiencing.

livenessProbe:
  httpGet:
    path: /
    port: 8080
    scheme: HTTP
  initialDelaySeconds: 15
  timeoutSeconds: 1
  periodSeconds: 10
  successThreshold: 1
  failureThreshold: 2
readinessProbe:
  httpGet:
    path: /
    port: 8080
    scheme: HTTP
  initialDelaySeconds: 15
  timeoutSeconds: 1
  periodSeconds: 10
  successThreshold: 1
  failureThreshold: 2

Stay tuned for our next adventure, where we continue to unravel the mysteries of the infrastructure world, one case at a time. Until then, keep your magnifying glasses handy and your curiosity alive.

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