Hidden Kubernetes Debugging Techniques That Senior DevOps Engineers Use

Hidden Pitfalls in kubectl exec and How to Overcome Them

The kubectl exec command is a powerful debugging tool, but DevOps engineers often hit unexpected roadblocks while using it. These issues usually come from container design choices and security settings rather than kubectl itself.

Why kubectl exec Fails in Minimal Images

Organizations build containers with minimal images to reduce attack surfaces and improve security. These optimized images don't deal very well with simple utilities that engineers take for granted. The command kubectl exec -it pod-name -- /bin/bash might fail with an error like "exec failed: unable to start container process: exec: '/bin/bash': stat /bin/bash: no such file or directory." This happens because minimal images, especially those based on Alpine Linux or distroless images, either have only sh instead of bash or no shell at all.

Here's how to fix this:

• Try using sh instead of bash: kubectl exec -it pod-name -- /bin/sh
• Use kubectl debug to attach an ephemeral container with debugging tools if containers lack any shell
• Specify the target container with -c container-name flag in multi-container pods

Security Restrictions and Non-root Access

Non-root containers are a security best practice but make debugging trickier. Containers running with non-root privileges through security contexts (runAsUser, runAsGroup) don't have permissions to access certain resources, especially device files.

Permission inheritance causes this issue. Kubernetes preserves the host device's user and group IDs when mounting device files into containers. A non-root container user often lacks the right group membership to access these devices, even if the device's group permissions would allow it.

The solution came with Kubernetes v1.22. You can enable the device_ownership_from_security_context flag in container runtimes like containerd and CRI-O. This setting automatically updates device ownership to match the container's runAsUser and runAsGroup values.

When to Avoid kubectl exec

kubectl exec shouldn't be your go-to debugging tool in several cases. Using exec to make configuration changes creates configuration drift between your source code and running containers. RBAC limitations make it impossible to restrict specific commands within an exec session, which creates security risks.

Heavy reliance on exec points to potential architectural issues. If your team needs constant shell access to containers, you might need better monitoring, logging, and instrumentation strategies. Production environments work best with non-intrusive debugging methods that don't risk destabilizing running workloads.

Debugging Kubernetes Pods with Ephemeral Containers

Standard kubectl exec might not cut it for troubleshooting. Ephemeral containers give you a better way to debug Kubernetes. This feature became stable in Kubernetes v1.25. Engineers can now add temporary debugging containers to running pods without any restarts.

How Ephemeral Containers Work in Kubernetes v1.25+

These containers are quite different from regular ones. They serve a specific purpose - running temporarily in an existing Pod to help you troubleshoot. Here's what makes ephemeral containers unique:

• They don't guarantee resources or execution
• You can't restart them automatically
• Port exposure isn't possible
• They don't work with liveness or readiness probes

You can create an ephemeral container with the kubectl debug command:

kubectl debug -it my-pod --image=busybox

This command gives you an interactive shell in a new busybox container inside your pod. The pod's ephemeralContainers list shows the container, but it won't restart after failure.

Using --target to Share Process Namespace

Debugging becomes more powerful when you target a specific container's process namespace:

kubectl debug -it my-pod --image=busybox --target=app-container

The --target parameter is a great way to get visibility into all processes running in that container. This helps you track down issues like high CPU usage or memory leaks.

On top of that, it lets you access the target container's filesystem through /proc/PID/root. You can check configuration files and logs easily.

Inspecting Container State with kubectl describe

You can check how your ephemeral container is doing with:

kubectl describe pod my-pod

The output has sections about the container's state, image, and runtime details. This helps you monitor the debug container while you work on fixes.

Cleaning Up Debug Containers Safely

Ephemeral containers stay in the pod specification even after they stop running. Here's how to clean up:

1. Finish your debugging work
2. Remove the pod if it was created just for debugging

Production pods need special care - create a copy with --copy-to instead of changing the original:

kubectl debug my-pod --image=ubuntu --share-processes --copy-to=debug-pod

This creates a separate debug pod that you can safely delete later without touching your original workload.

Creating Superdebug Containers with Volume and Env Mounts

Standard kubectl debug has limitations when troubleshooting complex applications, despite its ability to use ephemeral debug containers. DevOps engineers need access to the target container's volumes and environment variables to debug issues properly.

Limitations of Default kubectl debug

The kubectl debug command doesn't meet expectations when you work with containerized applications that depend on mounted volumes or environment-specific configurations. The ephemeral container's filesystem stays separate from the target container, though kubectl debug lets you inspect processes. This separation blocks access to mounted volumes with configuration files, logs, or data stores that are significant for debugging.

kubectl debug -it mypod --image=busybox --target=app-container

The debug container can't directly access the target's filesystem except through the /proc interface, which is limiting and awkward, even with the --target parameter sharing process namespaces.

Using kubectl-superdebug to Mount Volumes

Tools like kubectl-superdebug enhance standard debugging capabilities and solve these limitations:

kubectl superdebug --container=debug-container --image=alpine --target=postcont postpod

This solution works through these steps:

1. The running target container's specification gets retrieved
2. An ephemeral container patches into the pod
3. Process namespace sharing configures with the target container
4. The same volume mounts from the target container get included

Superdebug creates an exceptional debugging environment. The ephemeral container accesses the same persistent volumes, config maps, and secrets as the original container, unlike standard kubectl debug.

Copying Environment Variables from Target Container

Environment variables hold vital configuration information. You can extend the superdebug approach to copy environment variables from the target container:

kubectl superdebug --env-from-target --image=alpine --target=main-container pod-name

Applications that depend on environment variables work correctly during debugging sessions with this technique. The debug container automatically receives environment variables from ConfigMaps, Secrets, or direct pod specification, which preserves application behavior during troubleshooting.

Overlaying Debug Tools on Target Filesystem

Skilled engineers utilize techniques that overlay debugging tools onto the target filesystem:

kubectl debug -it --image=nixery.dev/shell/vim/ps/tshark <target>

This approach combines volume mounting capabilities with specialized debug images containing powerful tools. The nixery.dev method composes container images with requested debugging utilities automatically and chroots into the target's filesystem. You get a debugging experience similar to working directly within the target container, with all troubleshooting tools ready to use.

These advanced techniques help debug effectively in highly secured environments where containers run as non-root or use stripped-down distroless images.

Beyond Kubernetes: Native Namespace Debugging Tools

Kubernetes provides great debugging features, but complex scenarios need tools that can access Linux namespaces directly. These native debugging approaches go beyond standard Kubernetes commands and help engineers solve the trickiest problems.

Using kpexec for Namespace-Level Access

The kpexec tool expands debugging options by giving direct namespace-level access to running containers. This open-source kubectl plugin works differently from regular kubectl commands. It targets Linux namespaces instead of containers. This difference creates several advantages:

kubectl kpexec -n my-namespace my-pod -- /bin/sh

Engineers can see the actual namespace structure that powers Kubernetes abstractions this way. The kpexec tool lets you examine containers without shells or debugging utilities. This makes it a great way to get into minimal and distroless images where normal exec commands don't work.

Running Commands with Custom UID/GID

Standard debugging methods can't run processes as specific users. Native namespace tools solve this by letting engineers run commands with custom user and group IDs:

kubectl kpexec -n my-namespace my-pod --uid 1000 --gid 3000 -- id

This feature is vital to fix permission-related issues, especially when applications use non-root users through security contexts. Engineers can match the exact UID/GID of the application process to find and fix permission failures that might be hard to track down.

When to Use Non-Kubernetes Native Tools

Native namespace debugging tools become essential in these cases:

• Debugging minimal images that lack shells or troubleshooting utilities
• Investigating permission issues with specific user contexts
• Cases where security policies block standard kubectl debug commands
• Accessing host namespaces to troubleshoot network or filesystem issues
• Investigations that need deep kernel-level visibility

These tools should be used carefully since they bypass many Kubernetes security guardrails. Organizations should set up strict RBAC policies to control access to these powerful debugging features. Yes, it is important to make them available only to trusted engineers who have proper security training.

Conclusion

Master Kubernetes Debugging for Production Environments Senior DevOps engineers need more than simple commands to debug Kubernetes effectively. This piece explores sophisticated techniques they use to tackle complex cluster problems.

You should know the limits of kubectl exec. This becomes significant when you work with minimal container images or non-root containers. These constraints will force you to look for other options. On top of that, ephemeral containers give you powerful ways to troubleshoot running pods without disruption. This feature has been stable since Kubernetes v1.25.

Expert engineers create superdebug containers that mirror both volume mounts and target containers' environment variables. This approach will give a precise copy of production conditions during troubleshooting. Native namespace debugging tools let you dig even deeper when standard Kubernetes abstractions fall short.

The biggest difference between novice and expert Kubernetes practitioners lies in their debugging approach. Expert engineers don't just stick to familiar commands - they adapt their methods based on specific scenarios. They pick tools that balance diagnostic capability with system stability and security.

These debugging techniques help solve immediate problems and build deeper knowledge of Kubernetes internals. Engineers who know these methods can fix issues quickly while protecting production environments. As Kubernetes grows, these specialized debugging skills remain vital for anyone managing critical containerized applications.

FAQs

Q1. What are ephemeral containers in Kubernetes and how do they help with debugging?
Ephemeral containers are temporary containers added to running pods for troubleshooting purposes. They allow engineers to debug issues without restarting pods, making them ideal for investigating problems in production environments.

Q2. How can I debug Kubernetes pods with minimal or distroless images?
For minimal or distroless images, you can use tools like kubectl debug to attach an ephemeral container with debugging tools, or employ native namespace debugging tools like kpexec for direct access to container namespaces.

Q3. What are the limitations of using kubectl exec for debugging?
kubectl exec may fail in minimal images lacking a shell, can't be restricted to specific commands via RBAC, and its overuse may indicate architectural issues. It's also not ideal for making configuration changes as it can lead to configuration drift.

Q4. How can I access the same volumes and environment variables as the target container when debugging?
Tools like kubectl-superdebug allow you to create debug containers that mount the same volumes and copy environment variables from the target container, providing a more complete debugging environment.

Q5. When should I consider using non-Kubernetes native debugging tools?
Non-Kubernetes native tools are useful when debugging minimal images without shells, investigating permission issues, when kubectl debug is restricted by security policies, or when you need deep kernel-level visibility. However, use them cautiously as they bypass Kubernetes security measures.