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Curriculum 23: Advanced Output & Scripting

Custom Columns

12 min · 35 XP

Custom Columns Output

The -o custom-columns flag lets you define exactly which fields appear as columns in kubectl output. It produces clean, tabular results without the complexity of JSONPath or Go templates.

Inline Column Definitions

Columns are defined as comma-separated HEADER:JSONPATH pairs:

# Show pod name, status, and IP
kubectl get pods -o custom-columns=NAME:.metadata.name,STATUS:.status.phase,IP:.status.podIP

# Output:
# NAME        STATUS    IP
# my-app      Running   10.244.0.5
# web-server  Running   10.244.1.3

Each column uses JSONPath syntax to extract the value from the resource.

More Examples

# Nodes with their OS and kernel version
kubectl get nodes -o custom-columns=\
NODE:.metadata.name,\
OS:.status.nodeInfo.osImage,\
KERNEL:.status.nodeInfo.kernelVersion

# Deployments with replica counts
kubectl get deploy -o custom-columns=\
NAME:.metadata.name,\
DESIRED:.spec.replicas,\
READY:.status.readyReplicas,\
AVAILABLE:.status.availableReplicas

# Pods with container images
kubectl get pods -o custom-columns=\
POD:.metadata.name,\
IMAGE:.spec.containers[*].image

Column Definitions from a File

For reusable or complex column sets, save them to a file:

# columns.txt
NAME          NAMESPACE         STATUS              RESTARTS
.metadata.name  .metadata.namespace  .status.phase  .status.containerStatuses[0].restartCount

# Use the column definition file
kubectl get pods -o custom-columns-file=columns.txt

The file format uses the first line as headers and the second line as JSONPath expressions, separated by whitespace.

Combining with Other Flags

# Custom columns with sorting
kubectl get pods -o custom-columns=NAME:.metadata.name,RESTARTS:.status.containerStatuses[0].restartCount \
  --sort-by='.status.containerStatuses[0].restartCount'

# Custom columns across all namespaces
kubectl get pods -A -o custom-columns=\
NAMESPACE:.metadata.namespace,\
NAME:.metadata.name,\
NODE:.spec.nodeName

Key Takeaways

  • Custom columns use the format HEADER:.jsonpath.expression
  • Multiple columns are separated by commas
  • Store complex definitions in a file with custom-columns-file
  • Custom columns combine well with --sort-by and -A flags