KUBECTL — JSONPath

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tags:

• kubernetes
• containers
• docker

• sysadmin

  ☸️ KUBECTL — JSONPath Queries

Description / Описание: JSONPath is a query language for JSON data, integrated into kubectl via the -o jsonpath output format. It enables precise extraction of specific fields from Kubernetes resources without resorting to jq or grep. JSONPath is essential for automation scripts, CI/CD pipelines, and quick cluster inspection. Combined with custom-columns, it provides powerful tabular output directly from the Kubernetes API.

[!NOTE] When to use: JSONPath is built into kubectl and requires no additional tools. For complex filtering and transformation, consider combining with jq or using kubectl -o json | jq. / Когда использовать: JSONPath встроен в kubectl. Для сложной фильтрации комбинируйте с jq.

Basic JSONPath Queries

kubectl get pods -o jsonpath='{.items[*].status.podIP}'                            # All pod IPs / Все IP подов
kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\n"}{end}'        # Names one per line / Имена по одному в строке
kubectl get secret my -o jsonpath='{.data.password}' | base64 -d                   # Decode secret field / Декодировать поле секрета
kubectl get pods -o jsonpath='{.items[0].metadata.name}'                           # First pod name / Имя первого pod-а
kubectl get svc -o jsonpath='{.items[*].spec.clusterIP}'                           # All service IPs / Все IP сервисов

Resource Filtering

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

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

# Get services of type LoadBalancer
kubectl get svc -o jsonpath='{.items[?(@.spec.type=="LoadBalancer")].metadata.name}'

# Get pods without ready status
kubectl get pods -o jsonpath='{.items[?(@.status.conditions[?(@.type=="Ready")].status!="True")].metadata.name}'

Node Information

# Node names and kubelet versions
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.nodeInfo.kubeletVersion}{"\n"}{end}'

# Node capacity (CPU & memory) / Ёмкость
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\tCPU: "}{.status.capacity.cpu}{"\tMem: "}{.status.capacity.memory}{"\n"}{end}'

# Node allocatable resources
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.allocatable.cpu}{"\t"}{.status.allocatable.memory}{"\n"}{end}'

# Node external IPs
kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'

# Node OS information
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.nodeInfo.osImage}{"\n"}{end}'

Container & Image Queries

# Deployment → images
kubectl get deploy -o jsonpath='{range .items[*]}{.metadata.name}{" -> "}{.spec.template.spec.containers[*].image}{"\n"}{end}'

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

# Container resource requests
kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\n"}{range .spec.containers[*]}{"\t"}{.name}{" CPU: "}{.resources.requests.cpu}{" Mem: "}{.resources.requests.memory}{"\n"}{end}{end}'

# Container resource limits
kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\n"}{range .spec.containers[*]}{"\t"}{.name}{" CPU: "}{.resources.limits.cpu}{" Mem: "}{.resources.limits.memory}{"\n"}{end}{end}'

# Pod image pull policy
kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.containers[*].imagePullPolicy}{"\n"}{end}'

Custom Columns

# Custom columns for pods
kubectl get pods -o custom-columns=NAME:.metadata.name,STATUS:.status.phase,IP:.status.podIP,NODE:.spec.nodeName

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

# Deployments with replicas / Deployment-ы
kubectl get deploy -o custom-columns=NAME:.metadata.name,REPLICAS:.spec.replicas,AVAILABLE:.status.availableReplicas

# Services with type and IPs
kubectl get svc -o custom-columns=NAME:.metadata.name,TYPE:.spec.type,CLUSTER-IP:.spec.clusterIP,EXTERNAL-IP:.status.loadBalancer.ingress[0].ip

Troubleshooting JSONPath

# Pretty print JSON structure
kubectl get pod POD -o json | jq .

# Test JSONPath expressions
kubectl get pod POD -o jsonpath='{.metadata.name}'
kubectl get pod POD -o jsonpath='{.status.phase}'

# Common errors
# - Missing quotes around JSONPath expression
# - Incorrect array indexing
# - Missing range for multi-item output

# Combine with jq for complex queries
kubectl get pods -o json | jq '.items[] | select(.status.phase=="Running") | .metadata.name'

# Use grep/awk with JSONPath
kubectl get pods -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.phase}{"\n"}{end}' | grep Running

[!TIP] Use kubectl get <resource> -o json | jq . first to explore the JSON structure, then build your JSONPath query. / Используйте kubectl get <ресурс> -o json | jq . для изучения структуры JSON перед составлением JSONPath-запроса.

Documentation Links

• Kubernetes JSONPath Support: https://kubernetes.io/docs/reference/kubectl/jsonpath/
• kubectl Output Formatting: https://kubernetes.io/docs/reference/kubectl/#output-options
• JSONPath Specification: https://goessner.net/articles/JsonPath/
• jq Manual (complementary tool): https://jqlang.github.io/jq/manual/