What is kubectl?
kubectl is a CLI(Command Line Interface) client which can be used to interact with Kubernetes. Kubectl command line tool can be used in single node or multi-node cluster.
Installing the Kubernetes client (kubectl): Download and install appropriate format of kubectl client, all you need to do is download it and put it on your path.
Lets start with Kubectl commands to know about cluster and its building blocks. Generic Syntax to run kubectl commands from your terminal window:
kubectl [command] [TYPE] [NAME] [flags]
Please note :
1. Result of commands executed below has been masked(**********) intentionally, Please focus on command and its details.
2. clust_namespace1(is a pseudo namespace) in my cluster where I am running all commands.
- To know about kubernetes cluster components and config: Use "get cluster-info" commnd.
n0r0082@m-c02z31rnlvdt ~ % kubectl cluster-info Kubernetes control plane is running at https://master.********.k8s.us.walmart.net KubeDNS is running at
https://master.********.k8s.us.walmart.net/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy KubeDNSUpstream is running at
https://master.*********.k8s.us.walmart.net/api/v1/namespaces/*****kube-dns-upstream:dns/proxy kubernetes-dashboard is running at
https://master.*********.k8s.us.walmart.net/api/v1/namespaces/*****/kubernetes-dashboard:http/proxy monitoring-grafana is running at
https://master.*********.k8s.us.walmart.net/api/v1/namespaces/kube-system/*****/proxy node-local-dns is running at
https://master.*********.k8s.us.walmart.net/api/v1/namespaces/kube-system/***/proxy - Find all namespace in cluster: Use "get namespace" or "get ns" commandor
n0r0082@m-c02z31rnlvdt ~ % kubectl get namespace NAME STATUS AGE allspark-**** Active 570d ampplus-***** Active 390d **********-service Active 143d ap-***-ims-***-na Active 401d ap-****oom Active 578dn0r0082@m-c02z31rnlvdt ~ % kubectl get ns
- Find all nodes in cluster: Use "get node" command to find running master and workers nodes in cluster.
n0r0082@m-c02z31rnlvdt ~ % kubectl get node NAME STATUS ROLES AGE VERSION cp2-********-vmss000000 Ready control-plane,master 538d v1.20.13 cp2-********-vmss000001 Ready control-plane,master 538d v1.20.13 istio2-****-*****-vmss00012x Ready istio,node 16d v1.20.13 worker2-****-*****-vmss000fdm Ready node 16d v1.20.13 worker2-****-****-vmss000fdt Ready node 16d v1.20.13 - Find all pods in a cluster/namespace: Use "get pods" or "get po" command to fetch all pods in given name space.
Please note "-n <namespace_name>" is optional. In production env clusters are logically separated using namespace and resources are allocated accordingly.n0r0082@m-c02z31rnlvdt ~ % kubectl get pods -n clust_namespace1 NAME READY STATUS RESTARTS AGE prometheus-prometheus-0 3/3 Running 1 3d19h prometheus-prometheus-1 3/3 Running 1 16d ***-configuration-***-67696bb6c4-9z2rv 1/1 Running 0 5h58m ***-configuration-***-67696bb6c4-qr67q 1/1 Running 0 16d scale-up-***-configuration-***-1645963200-424xg 0/1 Completed 0 5h59m scale-up-***-configuration-***-1645963200-cjttf 0/1 Completed 0 5h59m- The kubectl get pods command doesn’t list any labels by default, but you can see them by using the --show-labels switch.
- List all pods in all namespaces using switch "--all-namespaces"
n0r0082@m-c02z31rnlvdt ~ % kubectl get pods --all-namespaces
- Find all pods in a cluster/namespace with labels: Resources in Kubernetes are attached with Labels. To list all pods with Labels use "--show-labels" flag. Labels are list of [key=value] paris separated by comma(",").
n0r0082@m-c02z31rnlvdt ~ % kubectl get po --show-labels -n clust_namespace1 NAME READY STATUS RESTARTS AGE LABELS ****-configuration-***-67696bb6c4-9z2rv 1/1 Running 0 6h6m
app.kubernetes.io/managed-by=kConfig,[KEY=VALUE],version=v1 ****-app-***-***-6d899d45cc-qrvkm 1/1 Running 0 4d10h
app.kubernetes.io/managed-by=kConfig,[KEY=VALUE],version=v1 - Find all pods in a cluster/namespace with specif Labels: Instead of listing all labels, if you’re only interested in certain labels, you can specify them with the -L switch and have each displayed in its own column.
n0r0082@m-c02z31rnlvdt ~ % kubectl get po -L app.kubernetes.io/name,env -n clust_namespace1 NAME READY STATUS RESTARTS AGE NAME ENV ******-******-5697c54f4b-fjm9p 1/1 Running 0 6h25m app1-config stage ******-******-5697c54f4b-z9mpb 1/1 Running 0 12d app2-config prod - Find pod details with custom columns: To display custom columns we can use "-o custom-columns".
Lets find IP Address of pod, IP Address of Host and application version# deployed. Host and Pod IP are not exposed with regular kubectl get commands. We can retrieve it from metadata.n0r0082@m-c02z31rnlvdt ~ % kubectl get pods -l app=my-app-namne -o custom-columns=NAME:.metadata.name,Pod-IP:.status.podIP,
Host-IP:.status.hostIP,Version:.metadata.labels.'app\.kubernetes\.io/version'
-n clust_namespace1 NAME Pod-IP Host-IP Version ************-54fb7b67fd-gczfq 11.16.2**.9* 10.33.18.** 1.0.2052 - Get pod details in verbose mode: Use "describe" command to fetch pod details in verbose mode.
n0r0082@m-c02z31rnlvdt ~ % kubectl describe pods my-pod-name -n clust_namespace1 Name: ******-****-*****-7fbd49bc47-ssdqx Namespace: clust_namespace1 Priority: 0 Priority Class Name: default Node: worker2-****-****-a2-vmss000i84/10.33.**.1** Start Time: Fri, 25 Feb 2022 20:05:39 -0800 Labels: app=***-*****-*****-sync ......
....... - Get all services in cluster/namespace: Use "get services" or "get svc" command to fetch all running services.
n0r0082@m-c02z31rnlvdt ~ % kubectl get svc -n clust_namespace1 NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE app-*****-stg** ClusterIP 10.50.2**.2**
8080/TCP,7766/TCP 416d app-*****-prod** ClusterIP 10.50.1**.1** 8080/TCP,7766/TCP 212d - Get all endpoints (IP:Port) details for running application:
n0r0082@m-c02z31rnlvdt ~ % kubectl get endpoints my_application_name -n clust_namespace1 NAME ENDPOINTS AGE my_application_name 11.17.43.54:7766,11.17.43.54:8080 479d
- To fetch all replicaset in cluster/namespace: Use "get rs" or "get replicaset" command.
n0r0082@m-c02z31rnlvdt ~ % kubectl get rs -n clust_namespace1 NAME DESIRED CURRENT READY AGE app-*****-*****-55bd787975 2 2 2 38d - Get all pods in cluster using selection condition: Using "--field-selector" we can fetch only running pods in cluster
n0r0082@m-c02z31rnlvdt ~ % kubectl get pods --field-selector=status.phase=Running
-n clust_namespace1 - Get all nodes (workers/master{control-plane}) in cluster: Using "--selector" we can include and exclude nodes.
To fetch only control-plane nodes, use label "node-role.kubernetes.io/master"n0r0082@m-c02z31rnlvdt ~ % kubectl get node --selector='node-role.kubernetes.io/master'
-n clust_namespace1 NAME STATUS ROLES AGE VERSION cp2-****-**-a2-vmss000000 Ready control-plane,master 538d v1.20.13 cp2-****-**-a2-vmss000001 Ready control-plane,master 538d v1.20.13
To fetch only workers nodes, use label "node-role.kubernetes.io/master"with negation(!)n0r0082@m-c02z31rnlvdt ~ % kubectl get node --selector='!node-role.kubernetes.io/master'
-n clust_namespace1 NAME STATUS ROLES AGE VERSION ....
......
Tags:
Kubernetes