kubectl JSONPath: Extract Exactly What You Need

# TIL: kubectl JSONPath: Extract Exactly What You Need

Stop piping kubectl output to grep, awk, and sed. JSONPath can get you exactly what you need in one command.

The Basic Pattern

kubectl get <resource> -o jsonpath='{<jsonpath-expression>}'

Simple Examples

Get Pod IPs

Get Pod Names Only

kubectl get pods -o jsonpath='{.items[*].metadata.name}'

Get Pod Name + IP

kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.podIP}{"\n"}{end}'

Real-World Use Cases

1. Find All Container Images

kubectl get pods -o jsonpath='{.items[*].spec.containers[*].image}' | tr ' ' '\n' | sort -u

2. Get Pods Not Running

kubectl get pods -o jsonpath='{range .items[?(@.status.phase!="Running")]}{.metadata.name}{"\t"}{.status.phase}{"\n"}{end}'

3. Find Pods Using Most Memory

kubectl top pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.usage.memory}{"\n"}{end}' | sort -k2 -h

4. Get All Node Capacities

kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.capacity.cpu}{" CPU\t"}{.status.capacity.memory}{" RAM\n"}{end}'

5. Find Secrets in a Namespace

kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.volumes[?(@.secret)].secret.secretName}{"\n"}{end}'

6. Get All Services and Their Type

kubectl get svc -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.type}{"\n"}{end}'

JSONPath Syntax Cheat Sheet

| Pattern | Description | Example | |---------|-------------|---------| | .items[*] | All items | Get all pods | | .items[0] | First item | Get first pod | | .items[0:3] | First 3 items | Get first 3 pods | | .items[-1] | Last item | Get last pod | | .items[?(@.field=="value")] | Filter | Pods where phase=Running | | {range .items[*]}...{end} | Loop | Iterate over items | | {"\n"} | Newline | Format output | | {"\t"} | Tab | Format output |

Advanced Filtering

Pods with Specific Label

kubectl get pods -l app=nginx -o jsonpath='{.items[*].metadata.name}'

Pods in Running State

kubectl get pods -o jsonpath='{.items[?(@.status.phase=="Running")].metadata.name}'

Containers in Waiting State

kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.containerStatuses[?(@.state.waiting)].name}{"\n"}{end}'

Pods with Restart Count > 0

kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.containerStatuses[0].restartCount}{"\n"}{end}' | awk '$2 > 0'

Useful Aliases

Add to your ~/.bashrc or ~/.zshrc:

# Get pod IPs
alias kip='kubectl get pods -o jsonpath='\''{range .items[*]}{.metadata.name}{"\t"}{.status.podIP}{"\n"}{end}'\'''

Get images alias kimages='kubectl get pods -o jsonpath='\''{.items[*].spec.containers[*].image}'\'' | tr " " "\n" | sort -u'

Get pod with most restarts alias krestart='kubectl get pods -o jsonpath='\''{range .items[*]}{.metadata.name}{"\t"}{.status.containerStatuses[0].restartCount}{"\n"}{end}'\'' | sort -k2 -n -r | head -1'

Get not ready pods alias knotready='kubectl get pods -o jsonpath='\''{range .items[?(@.status.phase!="Running")]}{.metadata.name}{"\t"}{.status.phase}{"\n"}{end}'\''' ```

Custom Columns (Even Better)

Sometimes custom columns are cleaner than JSONPath:

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

Node name, CPU, and memory kubectl get nodes -o custom-columns=NAME:.metadata.name,CPU:.status.capacity.cpu,MEMORY:.status.capacity.memory

Services and their ClusterIP kubectl get svc -o custom-columns=NAME:.metadata.name,TYPE:.spec.type,CLUSTER-IP:.spec.clusterIP ```

Common Patterns I Use Daily

1. Quick Debug: Get All Pod Info

kubectl get pod nginx-abc123 -o jsonpath='{range .spec.containers[*]}Name: {.name}{"\n"}Image: {.image}{"\n"}Ports: {.ports[*].containerPort}{"\n\n"}{end}'

2. Get All Environment Variables

kubectl get pod nginx-abc123 -o jsonpath='{range .spec.containers[*].env[*]}{.name}={.value}{"\n"}{end}'

3. Find Pods on a Specific Node

kubectl get pods --all-namespaces -o jsonpath='{range .items[?(@.spec.nodeName=="node-1")]}{.metadata.name}{"\t"}{.metadata.namespace}{"\n"}{end}'

4. Get ConfigMaps Used by Pods

kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.volumes[?(@.configMap)].configMap.name}{"\n"}{end}'

5. Network Policies Applied to Pods

kubectl get netpol -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.podSelector.matchLabels}{"\n"}{end}'

The Power Move

Combine JSONPath with watch for live updates:

watch -n 2 'kubectl get pods -o jsonpath='\''{range .items[*]}{.metadata.name}{"\t"}{.status.phase}{"\n"}{end}'\'''

Debugging JSONPath

If your JSONPath isn't working, test it step by step:

# Get full JSON first
kubectl get pod nginx-abc123 -o json | jq '.'

Then build your JSONPath incrementally kubectl get pod nginx-abc123 -o jsonpath='{.metadata}' kubectl get pod nginx-abc123 -o jsonpath='{.metadata.name}' kubectl get pod nginx-abc123 -o jsonpath='{.status}' kubectl get pod nginx-abc123 -o jsonpath='{.status.phase}' ```

The Gotcha

JSONPath in kubectl has some quirks:

1. **Filters must use `@`**: `.items[?(@.field=="value")]` not `.items[?(.field=="value")]`
2. **Arrays need `[*]`**: `.items[*]` not `.items[]`
3. **Quotes matter**: Use single quotes outside, double inside: `'{.items[?(@.name=="value")]}'`

This has eliminated so much grep | awk | sed pipeline complexity from my daily kubectl commands. One-liner power!