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JSON Path

is a query language

  • DATA
{
   "car": {
      "color": "blue",
      "price": "$20,000"
   }
}

  • Query Get car details car

  • Result

{
  "color": "blue",
  "price": "$20,000"
}

JSON PATH-Dictionaries

Dic

JSON PATH-Lists

DATA:

[
 "car",
 "bus",
 "truck",
 "bike"
]

Query: Get the 1st element $[0]

Get the 1st and 4th element $[0,3]

Result: [ "car" ] [ "car", "bike" ]

JSON PATH-Dictionary & Lists

DATA:

{
  "car": {
     "color": "blue"
     "price": "$20,000"
     "wheels": [
       {
          "model": "X345ERT",
          "location": "front-right"
       },
       {
          "model": "X346GRX",
          "location": "front-right"
       },
       {
          "model": "X236DEM",
          "location": "rear-right"
       },
       {
          "model": "X987XMV",
          "location": "rear-right"
       },
     ]
  }
}

QUERY: #$ is root element Get the model of the 2nd wheel $.car.wheels[1].model or $.car.wheels[?(@.location == "rear-right")].model Result: X346GRX

JSON PATH-Criteria

DATA:

[
 12,
 43,
 23,
 12,
 56,
 43,
 93,
 32,
 45,
 63,
 27,
 8,
 78
]

QUERY: list all number > 40 Get all numbers greater than 40 $[ Check if each item in the array > 40 ] Check if => ? () $[?( each each item in the array > 40 )] each iteam in the list => @ $[?( @ > 40 )] @ == 40 @ in [40,43,45] @ != 40 @ nin [40,43,45]

RESULT:

[
 43,
 56,
 43,
 93,
 45,
 63,
 78
]

Wild card

DATA:

{
  "car": {
     "color": "blue"
     "price": "$20,000"
   },
  "bus": {
     "color": "white"
     "price": "$120,000"
   }
}
QUERY:
Get all colors
`$.*.color`
Get all prices
`$.*.price`
RESULT:
[ "blue", "white" ]

---
DATA:
``` json
[
  {
     "model": "X345ERT",
     "location": "front-right"
  },
  {
     "model": "X346GRX",
     "location": "front-right"
  },
  {
     "model": "X236DEM",
     "location": "rear-right"
  },
  {
     "model": "X987XMV",
     "location": "rear-right"
  }
]

QUERY: Get 1st wheel's model $[0].model Get 4st wheel's model $[3].model Get all wheel's model $[*].model

DATA: Data QUERY: Get car's 1st wheel model $.car.wheels[0].model Get car's all wheel model $.car.wheels[*].model Get bus's wheel models $.bus.wheels[*].model Get all wheels' models $.*.wheels[*].model Result: result

List

QUERY:

$[0:8]
START:END
$[0:8:2]
START:END:STEP
# Get the last element
$[-1:0]
$[-1:]
# Get the last 3 elements
$[-3:]

Why json path?

  • Large data sets
    • 100s of Nodes
    • 1000s of PODs, Deployments, ReplicaSets

Kubectl

kubectl get nodes kubectl talk to kube-apiserver, kube-apiserver speaks json language, it return the result with json format. k get nodes -o wide # show more details

How to JSON path in kubectl?

  1. Indentify the kubectl command
  2. Familarize with JSON output
k get nodes -o json
k get pods -o json
  1. Form the JSON PATH query .items[0].spec.containers[0].image
  2. Use the JSON PATH query with kubectl command k get pods -o=jsonpath='{ .items[0].spec.containers[0].image } JSON Path example

Loops -Range

k get nodes -o=jsonpath='{.items[*].metadata.name{"\n"}{.items[*].status.capacity.cpu}' FOR EACH NODE PRINT NODE NAME \t PRINT CPU COUNT \n END FOR

'{range .items[*]}
   {.metadata.name}{"\t"} {.status.capacity.cpu}{"\n"}
{end}'

k get nodes -o=custom-colums=<COLUMN NAME>:<JSON PATH>

k get nodes -o=custom-colums=NODE:.metadata.name,CPU:.status.capacity.cpu
NODE     CPU
master    4
node01    4

JSON PATH for Sort

k get nodes -o=custom-colums=NODE:.metadata.name, CPU=.status.capacity.cpu
NODE   CPU
master  4
node01  4
k get nodes --sort-by= .metadata.name
k get nodes --sort-by= .status.capacity.cpu

LAB

The order of container could be different. The redis-container need not be the second container all the time. So, re-develop a JSON PATH query to get the restart count of redis-container, but this time use a criteria/condition to get the restart count of the container with the container name redis-container .

Scroll down if you can't see the status section

Source Data:

{
  "apiVersion": "v1",
  "kind": "Pod",
  "metadata": {
    "name": "nginx-pod",
    "namespace": "default"
  },
  "spec": {
    "containers": [
      {
        "image": "nginx:alpine",
        "name": "nginx"
      },
      {
        "image": "redis:alpine",
        "name": "redis-container"
      }
    ],
    "nodeName": "node01"
  },
  "status": {
    "conditions": [
      {
        "lastProbeTime": null,
        "lastTransitionTime": "2019-06-13T05:34:09Z",
        "status": "True",
        "type": "Initialized"
      },
      {
        "lastProbeTime": null,
        "lastTransitionTime": "2019-06-13T05:34:09Z",
        "status": "True",
        "type": "PodScheduled"
      }
    ],
    "containerStatuses": [
      {
        "image": "nginx:alpine",
        "name": "nginx",
        "ready": false,
        "restartCount": 4,
        "state": {
          "waiting": {
            "reason": "ContainerCreating"
          }
        }
      },
      {
        "image": "redis:alpine",
        "name": "redis-container",
        "ready": false,
        "restartCount": 2,
        "state": {
          "waiting": {
            "reason": "ContainerCreating"
          }
        }
      }
    ],
    "hostIP": "172.17.0.75",
    "phase": "Pending",
    "qosClass": "BestEffort",
    "startTime": "2019-06-13T05:34:09Z"
  }
}

Expected Output:

[
  2
]

Answer: `$.status.containerStatuses[?(@.name == 'redis-container')].restartCount**

advanced kubectl commands Use a JSON PATH query to identify the context configured for the aws-user in the my-kube-config context file and store the result in /opt/outputs/aws-context-name. kubectl config view --kubeconfig=my-kube-config -o jsonpath="{.contexts[?(@.context.user=='aws-user')].name}" > /opt/outputs/aws-context-name