Kubernetes Ephemeral Containers: Enhancing Security and Streamlining Troubleshooting in Production Clusters

Ephemeral containers in Kubernetes are a powerful feature that allows operators to debug and troubleshoot running Pods by creating short-lived containers within the same Pod. This is particularly helpful for issues that cannot be replicated in a separate environment. By using ephemeral containers, you can attach a container to a running Pod, inspect the file system, network settings, or running processes, and then discard the container without affecting the Pod’s primary containers.

What Are Ephemeral Containers?

Ephemeral containers are special containers that do not run as part of an application workload but are instead added to an existing Pod for the purpose of debugging. They share the same resources (network namespace, volumes, etc.) as the other containers in the Pod, making them ideal for real-time diagnosis. Once debugging is complete, the ephemeral container can be removed without needing to recreate the entire Pod.

Key Points

• Short-lived: Ephemeral containers are meant only for debugging or troubleshooting.
• Non-disruptive: They do not impact existing application containers in the Pod.
• Resource-Sharing: They share resources like storage volumes and network namespaces with the Pod, making debugging more powerful.

Security Considerations With Ephemeral Containers

Ephemeral containers provide a safer debugging approach by limiting prolonged access to production Pods. You can enforce strict RBAC rules so only authorized users can add and run ephemeral containers, minimizing the window for potential threats. Because these containers vanish once debugging is done, the attack surface is reduced, reinforcing overall cluster security.

Use Cases

• Troubleshooting Application Crashes: When you need to inspect logs or run debugging tools in a crashed or crashing container, ephemeral containers let you enter a running environment without altering the main container’s configuration.
• Network Debugging: You can install debugging tools (e.g., tcpdump, netstat) in the ephemeral container to diagnose network issues within the Pod’s network namespace.
• Live File System Checks: If you suspect file corruption or incorrect file paths, ephemeral containers let you check the file system in real time.

Prerequisites

• Kubernetes Version: Ephemeral containers require at least Kubernetes 1.23+ where the EphemeralContainers feature is generally available (GA). On older Kubernetes versions, you might need to enable the feature gate EphemeralContainers.
• kubectl: Make sure your local kubectl client is at least the same or newer version than your cluster’s control plane.
• Sufficient RBAC Permissions: You need permission to use the kubectl debug command and to update Pods (the ephemeral container is added via an update to the Pod’s specification).

Step-by-Step Guide: Using Ephemeral Containers

Below is a generalized process that will work on any Kubernetes environment, including EKS (Elastic Kubernetes Service on AWS), AKS (Azure Kubernetes Service), GKE (Google Kubernetes Engine), or on-premises clusters. We will focus on the kubectl debug command, which is the primary mechanism for adding ephemeral containers.

Verify Your Cluster’s Configuration

kubectl version

• Ensure that your Server Version is at least 1.23.
• Confirm that your Client Version is also compatible.

If you are on a managed environment like EKS or AKS, check the cluster version from your cloud provider’s dashboard or CLI to ensure it’s 1.23 or later.

Identify the Pod You Want to Debug

List Pods in a specific namespace:

kubectl get pods -n <your-namespace>

Pick the Pod name you need to troubleshoot, for example: my-app-pod-abc123.

Add an Ephemeral Container Using kubectl debug

Use the kubectl debug command to add an ephemeral container. For example, we’ll use a simple Ubuntu image:

kubectl debug my-app-pod-abc123 -n <your-namespace> \
  --image=ubuntu \
  --target=my-container \
  --interactive=true \
  --tty=true

Here’s a breakdown of the flags:

• my-app-pod-abc123: The name of the existing Pod.
• --image=ubuntu: Docker image to use for the ephemeral container.
• --target=my-container: (Optional) Specifies which container in the Pod you want to target for namespace sharing. Typically, this is the main container in the Pod.
• --interactive=true and --tty=true: Allows you to get a shell session inside the ephemeral container.

Once you run the above, you will get a shell prompt in the ephemeral container inside the existing Pod. You can now run debugging commands like ls, ps, netstat, or install extra packages.

Confirm Ephemeral Container Creation

In another terminal, or after exiting the ephemeral container’s shell, run:

kubectl get pod my-app-pod-abc123 -n <your-namespace> -o yaml

You should see a new section under spec or status describing the ephemeral container.

Debug and Troubleshoot

From within the ephemeral container, you can:

• Check logs or app configuration.
• Use debugging tools like curl, wget, telnet to verify network connectivity.
• Inspect environment variables to confirm your application’s configuration.

# Examples
curl http://localhost:8080/health
env | grep MY_APP_
ps aux

Clean Up Ephemeral Containers

Ephemeral containers are removed automatically when the Pod is destroyed or after you remove them manually. To remove the ephemeral container from the Pod without destroying the entire Pod (on supported versions), you can patch the Pod spec. However, typically ephemeral containers are not meant to be long-lived. Once you delete the Pod or scale down your deployment, the ephemeral container will also be removed.

Specific Notes for Managed Services

Amazon EKS

• Ensure your EKS cluster is running Kubernetes 1.23 or higher.
• Confirm that the IAM permissions allow you to perform kubectl debug.
• If you’re using older EKS versions (1.22 or earlier), you’ll need to enable the EphemeralContainers feature gate.

Azure AKS

• Use the Azure CLI (az aks update) to upgrade your AKS cluster to a compatible version if necessary.

Confirm your kubectl context is set to the AKS cluster:

az aks get-credentials --resource-group <rg-name> --name <cluster-name>

Other Managed or On-Prem Clusters

• Check your cluster’s documentation or ask your provider to confirm ephemeral containers are enabled.
• Most modern on-prem solutions (OpenShift, Rancher, etc.) have ephemeral containers enabled by default from Kubernetes 1.23 onwards, but you may have to manually enable the feature gate if you are on an older version.

Best Practices

• Use Minimal Images: Choose lightweight images to reduce overhead (e.g., busybox, distroless debugging images).
• Restrict RBAC: Limit who can create ephemeral containers to minimize potential security risks.
• Log All Debug Sessions: Keep track of ephemeral container usage for auditing and compliance.
• Don’t Depend on Ephemeral Containers: They’re for debugging only. If you need a permanent sidecar or helper container, configure it in the Pod spec from the start.

Conclusion

Ephemeral containers are a versatile and powerful way to troubleshoot issues in real time without impacting the primary application containers. Whether you’re running Kubernetes on EKS, AKS, on-prem, or another managed solution, understanding and using ephemeral containers can significantly decrease your mean-time-to-recovery (MTTR) and improve operational efficiency.

They complement traditional troubleshooting methods and should be part of any platform team’s toolkit for diagnosing complex application issues. By following the steps outlined above, you can confidently deploy ephemeral containers in your environment and streamline your debugging processes.

Author’s Note: Drawn from real-world Kubernetes troubleshooting, this guide aims to help you debug Pods swiftly and without disruption in Production Environments.