Creating Ephemeral Kubernetes Exec Pods

Creating Ephemeral Kubernetes Exec Pods

Create a dedicated pod cloned from an existing deployment for interactive shell access with full application context (environment variables, secrets, volume mounts).

When to Use This

• Running Rails console in a Kubernetes environment
• Executing database migrations or one-off scripts
• Debugging with full app configuration
• Running commands that would disrupt a live pod

Why not kubectl exec into an existing pod? This approach:

• Won't affect production traffic
• Has configurable resources (memory/CPU)
• Stays alive for your session only
• Can run disruptive commands safely

Prerequisites

• kubectl installed and configured
• jq installed (for JSON transformation)
• Kubeconfig with access to target cluster
• Know your target:
  • Namespace where the app runs
  • Label selector to find the deployment
  • Main app container name (not sidecars)

AWS SSO Authentication (if applicable)

If your cluster uses AWS EKS with SSO authentication:

# Check if SSO session is valid
kubectl get deployments -n <NAMESPACE> 2>&1 | grep -q "SSO session" && echo "SSO expired"

# Find the AWS profile from your kubeconfig
grep -A15 'exec:' <KUBECONFIG_PATH> | grep 'AWS_PROFILE' -A1

# Login with the profile
aws sso login --profile <PROFILE_NAME>

Usage

Important: Keep the same terminal session open throughout. Variables must persist across all steps.

Step 1: Set up environment

export KUBECONFIG=/path/to/your/kubeconfig

Step 2: Find the source deployment

# List matching deployments
kubectl get deployments -n <NAMESPACE> -l <LABEL_SELECTOR>

# Pick one and store the name
DEPLOYMENT_NAME=<name-from-output>

# List containers to find the app container (not sidecars like linkerd-proxy, proxy, envoy)
kubectl get deployment "$DEPLOYMENT_NAME" -n <NAMESPACE> -o jsonpath='{.spec.template.spec.containers[*].name}'

# The app container usually matches the deployment name
CONTAINER_NAME=<app-container-name>
NAMESPACE=<namespace>

Step 3: Extract and transform to pod spec

# Generate a unique pod name
POD_NAME="${DEPLOYMENT_NAME}-exec-`date +%s`"
echo "Pod name: $POD_NAME"

# Extract deployment and transform to ephemeral pod
kubectl get deployment "$DEPLOYMENT_NAME" -n "$NAMESPACE" -o json | jq \
  --arg podname "$POD_NAME" \
  --arg namespace "$NAMESPACE" \
  --arg container "$CONTAINER_NAME" '
  .spec.template |
  .apiVersion = "v1" |
  .kind = "Pod" |
  .metadata = {name: $podname, namespace: $namespace, labels: {ephemeral: "true"}} |
  .spec.restartPolicy = "Never" |
  .spec.containers = [.spec.containers[] | select(.name == $container) | .command = ["sleep", "14400"] | .args = [] | del(.readinessProbe) | del(.livenessProbe) | del(.startupProbe)] |
  del(.spec.initContainers)
' > /tmp/exec-pod.json

# Verify the pod spec looks correct
jq '{name: .metadata.name, namespace: .metadata.namespace, containers: [.spec.containers[].name]}' /tmp/exec-pod.json

This creates a pod that:

• Extracts only the app container (strips sidecars)
• Copies env vars, volumes, secrets from the source
• Runs sleep 14400 (4 hours) instead of the app's entrypoint
• Removes probes (they'd fail since the app isn't running)

Step 4: Optionally adjust memory

# If you need more memory (e.g., 1024Mi):
jq '.spec.containers[0].resources = {
  limits: {memory: "1024Mi"},
  requests: {memory: "1024Mi"}
}' /tmp/exec-pod.json > /tmp/exec-pod-final.json && mv /tmp/exec-pod-final.json /tmp/exec-pod.json

Step 5: Create and wait for the pod

kubectl apply -f /tmp/exec-pod.json
kubectl wait --for=condition=Ready "pod/$POD_NAME" -n "$NAMESPACE" --timeout=120s

Step 6: Exec into the pod

# Interactive shell
kubectl exec -it "$POD_NAME" -n "$NAMESPACE" -- bash

# Or run Rails console directly
kubectl exec -it "$POD_NAME" -n "$NAMESPACE" -- bin/rails console

Cleanup

Always delete the pod when done:

kubectl delete pod "$POD_NAME" -n "$NAMESPACE" --grace-period=1

Find orphaned exec pods:

kubectl get pods -n "$NAMESPACE" -l ephemeral=true

Troubleshooting

Lost your variables (new terminal session)

export KUBECONFIG=/path/to/your/kubeconfig
NAMESPACE=<namespace>

# Find your most recent exec pod
POD_NAME=$(kubectl get pods -n "$NAMESPACE" -l ephemeral=true --sort-by=.metadata.creationTimestamp -o jsonpath='{.items[-1:].metadata.name}')
echo "Found pod: $POD_NAME"

SSO session expired

The SSO session associated with this profile has expired or is otherwise invalid.

Re-authenticate with aws sso login --profile <PROFILE_NAME>.

Pod stuck in Pending

kubectl describe pod "$POD_NAME" -n "$NAMESPACE"

Common causes: insufficient cluster resources, node selector can't be satisfied, image pull secrets missing.

ImagePullBackOff

Check image pull secrets are included:

kubectl get deployment "$DEPLOYMENT_NAME" -n "$NAMESPACE" -o jsonpath='{.spec.template.spec.imagePullSecrets}'

OOMKilled

Pod ran out of memory. Recreate with higher memory value in step 4.

Container has no bash

Try sh instead:

kubectl exec -it "$POD_NAME" -n "$NAMESPACE" -- sh

Variations

Run a one-off command:

kubectl exec "$POD_NAME" -n "$NAMESPACE" -- bin/rails runner "puts User.count"

Shorter timeout (1 hour): In step 3, change "sleep", "14400" to "sleep", "3600".

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