How to use jsonpath to retrieve details for k8s cluster

Table of Content

The jsonpath is used to filter specific fields from json tree in k8s cluster.

pod json

first of all we need to understand and familiar with json tree structure for pod.

kubectl get pods -o json

from output we will see top level objects:

 
- apiVersion
- items
    - metadata
    - spec
        - containers
        - volumes
    - status
        - hostIP
        - podIP

vagrant@master:~$ kubectl get po -o wide
vagrant@master:~$ kubectl get po -o json

if just want to get some info quickly and not very familiar with jsonpath filter syntax, you can grep keyword,

vagrant@master:~$ kubectl get po -o json |grep podIP -A 3

However would be better to know how jsonpath filter syntax works to get expected result quickly and precisely. You don’t know all but at least basic one.

search pod ip

vagrant@master:~$ kubectl get pods test -o=jsonpath='{.status.podIP}{"\n"}'
192.168.171.66

or

vagrant@master:~$ kubectl get pods -o=jsonpath='{.items[0].status.podIP}{"\n"}'
192.168.171.66

search all pods ip

kubectl get pods -o=jsonpath="{.items[*]['metadata.name', 'status.podIP']}"
test web-96d5df5c8-6l5nx web-96d5df5c8-x5rs8 192.168.171.66 192.168.171.68 192.168.171.67

string output looks better on format,


   "status":  
      "podIP": "192.168.120.3",
                "podIPs": [
                    {
                        "ip": "192.168.120.3"
                    }
                ],

vagrant@master:~$ kubectl get pods -o=jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.podIP}{"\n"}{end}'
test    192.168.171.66
web-96d5df5c8-6l5nx     192.168.171.68
web-96d5df5c8-x5rs8     192.168.171.67

List all containerIDs of initContainer of all pods

        "status":
            "initContainerStatuses": [
                    {
                        "containerID": "docker://0bc99ad1ed453c7057dd79eac20ce6448fc2f8dbd52accfba7e57d4fbeeab070",

kubectl get pods --all-namespaces -o jsonpath='{range .items[*].status.initContainerStatuses[*]}{.containerID}{"\n"}{end}' | cut -d/ -f3
0bc99ad1ed453c7057dd79eac20ce6448fc2f8dbd52accfba7e57d4fbeeab070
c39f99eea893d94e26972a3b8210cc18da15db50248031e6991dd18eb980abfd
8793729fbf41b319adc629885d9c5d4f26d82c9bcd606a5a1e1446d1c0e7e862
558dd5e0ce7fa442350b67cedc1ffb5fb525ac61c6e4c6022f4acbbc92c03121List all containerIDs of initContainer of all pods

send command to all pods

vagrant@master:~$ kubectl get po -o jsonpath={.items..metadata.name}
test web-96d5df5c8-6l5nx web-96d5df5c8-x5rs8

vagrant@master:~$ for pod in $(kubectl get po -o jsonpath={.items..metadata.name}); do echo $pod && kubectl exec -it $pod env; done
test
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=test
TERM=xterm
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
KUBERNETES_SERVICE_HOST=10.96.0.1
NGINX_VERSION=1.21.3
NJS_VERSION=0.6.2
PKG_RELEASE=1~buster
HOME=/root
web-96d5df5c8-6l5nx
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=web-96d5df5c8-6l5nx
TERM=xterm
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
KUBERNETES_SERVICE_HOST=10.96.0.1
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP_PORT=443
NGINX_VERSION=1.21.3
NJS_VERSION=0.6.2
PKG_RELEASE=1~buster
HOME=/root
web-96d5df5c8-x5rs8
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=web-96d5df5c8-x5rs8
TERM=xterm
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
KUBERNETES_SERVICE_HOST=10.96.0.1
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP_PORT=443
NGINX_VERSION=1.21.3
NJS_VERSION=0.6.2
PKG_RELEASE=1~buster
HOME=/root

get all containers image in order

"containers": [
                    {
                        "args": [
                            "--secure-port=5443"
                        ],
                        ...
                        ],
                        "image": "docker.io/calico/apiserver:v3.20.2",

vagrant@master:~$ kubectl get pods --all-namespaces -o jsonpath="{.items[*].spec.containers[*].image}" |\
 tr -s '[[:space:]]' '\n' |\
 sort |\
 uniq -c
      1 docker.io/calico/apiserver:v3.20.2
      1 docker.io/calico/kube-controllers:v3.20.2
      2 docker.io/calico/node:v3.20.2
      2 docker.io/calico/typha:v3.20.2
      2 k8s.gcr.io/coredns/coredns:v1.8.4
      1 k8s.gcr.io/etcd:3.5.0-0
      1 k8s.gcr.io/kube-apiserver:v1.22.3
      1 k8s.gcr.io/kube-controller-manager:v1.22.3
      2 k8s.gcr.io/kube-proxy:v1.22.3
      1 k8s.gcr.io/kube-scheduler:v1.22.3
      3 nginx
      1 quay.io/tigera/operator:v1.20.4

node json

vagrant@master:~$ kubectl get node -o json
{
    "apiVersion": "v1",
    "items": [
        {
            "apiVersion": "v1",
            "kind": "Node",
            "metadata": {
...
}

list all nodes InternalIP and ExternalIP

good example for search condition


"status": {
                "addresses": [
                    {
                        "address": "192.168.120.2",
                        "type": "InternalIP"
                    },
                    {
                        "address": "master",
                        "type": "Hostname"
                    }
                ],

vagrant@master:~$ kubectl get nodes -o jsonpath='{.items[*].status.addresses}'
[{"address":"192.168.120.2","type":"InternalIP"},{"address":"master","type":"Hostname"}] [{"address":"192.168.120.3","type":"InternalIP"},{"address":"worker","type":"Hostname"}]

vagrant@master:~$ kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'
vagrant@master:~$ kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="InternalIP")].address}'
192.168.120.2 192.168.120.3

search all nodes in Ready status

vagrant@master:~$ JSONPATH='{range .items[*]}{@.metadata.name}:{range @.status.conditions[*]}{@.type}={@.status};{end}{end}' \
>  && kubectl get nodes -o jsonpath="$JSONPATH" | grep "Ready=True"
master:NetworkUnavailable=False;MemoryPressure=False;DiskPressure=False;PIDPressure=False;Ready=True;worker:NetworkUnavailable=False;MemoryPressure=False;DiskPressure=False;PIDPressure=False;Ready=True;

list all tainted status


"spec": {
                "podCIDR": "192.168.0.0/24",
                "podCIDRs": [
                    "192.168.0.0/24"
                ],
                "taints": [
                    {
                        "effect": "NoSchedule",
                        "key": "role",
                        "value": "admin"
                    }

vagrant@master:~$ kubectl taint nodes master role=admin:NoSchedule
node/master tainted
vagrant@master:~$ kubectl get nodes -o jsonpath="{range .items[*]}{.metadata.name} {.spec.taints[?(@.effect=='NoSchedule')].effect}{\"\n\"}{end}"
master NoSchedule
worker

config json

vagrant@master:~$ kubectl config view -o json
{
    "kind": "Config",
    "apiVersion": "v1",
    "preferences": {},
    "clusters": [
        {
            "name": "kubernetes",
            "cluster": {
                "server": "https://192.168.120.2:6443",
                "certificate-authority-data": "DATA+OMITTED"
            }
        }
    ],
    "users": [
        {
            "name": "kubernetes-admin",
            "user": {
                "client-certificate-data": "REDACTED",
                "client-key-data": "REDACTED"
            }
        }
    ],
...    
}

get all users

vagrant@master:~$ kubectl config view -o jsonpath='{.users[*].name}'
kubernetes-admin

get one user details

 
nvagrant@master:~$ kubectl config view -o jsonpath='{.users[?(@.name == "kubernetes-admin")].user}'
{"client-certificate-data":"REDACTED","client-key-data":"REDACTED"}