How to Read Nodes in Kubernetes [Quick K8s Tip]

This quick Kubernetes tip helps you to get details about a Kubernetes worker node and how to read and understand its output.

What is a Kubernetes node?

A node is a worker machine (virtual/physical) in Kubernetes where pods carrying your applications run. The services which runs on a node include Docker, kubelet and kube-proxy.

Listing available nodes in your Kubernetes cluster

The simplest way to see the available nodes is by using the kubectl command in this fashion:

kubectl get nodes

It should show you all the nodes in your cluster at a glance. You can see the status, role, age and version of each node.

root@kmaster-rj:~# kubectl get nodes
NAME          STATUS   ROLES    AGE   VERSION
kmaster-rj    Ready    master   39d   v1.18.8
kworker-rj1   Ready    <none>   39d   v1.18.8
kworker-rj2   Ready    <none>   39d   v1.18.8
root@kmaster-rj:~#

As you can see both the worker nodes are in ready state.

In order to view a more detailed output run following command, you can add the -o wide option like this:

kubectl get nodes -o wide

Now you'll see additional details like internal and external IP, container image, kernel version and runtime for the container.

root@kmaster-rj:~# kubectl get nodes -o wide
NAME          STATUS   ROLES    AGE   VERSION   INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION       CONTAINER-RUNTIME
kmaster-rj    Ready    master   39d   v1.18.8   172.42.42.200   <none>        Ubuntu 18.04.5 LTS   4.15.0-101-generic   docker://19.3.6
kworker-rj1   Ready    <none>   39d   v1.18.8   172.42.42.201   <none>        Ubuntu 18.04.4 LTS   4.15.0-101-generic   docker://19.3.6
kworker-rj2   Ready    <none>   39d   v1.18.8   172.42.42.202   <none>        Ubuntu 18.04.5 LTS   4.15.0-101-generic   docker://19.3.6

Let's go deeper and know more about a specific node.

Describing a node for more details

If you want detailed information on a specific node, you can use the kubectl describe command with the node name:

kubectl describe nodes worker-node-name

Here's a sample output:

root@kmaster-rj:~# kubectl describe nodes kworker-rj1
Name:               kworker-rj1
Roles:              <none>
Labels:             app=front-end
                    beta.kubernetes.io/arch=amd64
                    beta.kubernetes.io/os=linux
                    kubernetes.io/arch=amd64
                    kubernetes.io/hostname=kworker-rj1
                    kubernetes.io/os=linux
                    size=medium
Annotations:        kubeadm.alpha.kubernetes.io/cri-socket: /var/run/dockershim.sock
                    node.alpha.kubernetes.io/ttl: 0
                    projectcalico.org/IPv4Address: 172.42.42.201/24
                    projectcalico.org/IPv4IPIPTunnelAddr: 172.16.213.0
                    volumes.kubernetes.io/controller-managed-attach-detach: true
CreationTimestamp:  Sun, 02 Aug 2020 15:42:32 +0000
Taints:             app=front-end:NoExecute
Unschedulable:      false
Lease:
  HolderIdentity:  kworker-rj1
  AcquireTime:     <unset>
  RenewTime:       Fri, 11 Sep 2020 07:09:51 +0000
Conditions:
  Type                 Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
  ----                 ------  -----------------                 ------------------                ------                       -------
  NetworkUnavailable   False   Fri, 11 Sep 2020 02:57:12 +0000   Fri, 11 Sep 2020 02:57:12 +0000   CalicoIsUp                   Calico is running on this node
  MemoryPressure       False   Fri, 11 Sep 2020 07:06:56 +0000   Fri, 28 Aug 2020 06:33:29 +0000   KubeletHasSufficientMemory   kubelet has sufficient memory available
  DiskPressure         False   Fri, 11 Sep 2020 07:06:56 +0000   Fri, 28 Aug 2020 06:33:29 +0000   KubeletHasNoDiskPressure     kubelet has no disk pressure
  PIDPressure          False   Fri, 11 Sep 2020 07:06:56 +0000   Fri, 28 Aug 2020 06:33:29 +0000   KubeletHasSufficientPID      kubelet has sufficient PID available
  Ready                True    Fri, 11 Sep 2020 07:06:56 +0000   Fri, 11 Sep 2020 02:56:03 +0000   KubeletReady                 kubelet is posting ready status. AppArmor enabled
Addresses:
  InternalIP:  172.42.42.201
  Hostname:    kworker-rj1
Capacity:
  cpu:                2
  ephemeral-storage:  64800356Ki
  hugepages-2Mi:      0
  memory:             2040812Ki
  pods:               110
Allocatable:
  cpu:                2
  ephemeral-storage:  59720007991
  hugepages-2Mi:      0
  memory:             1938412Ki
  pods:               110
System Info:
  Machine ID:                 c7dbeba40d7b45a387082c96df6cc554
  System UUID:                595C28CA-DBBF-304D-8C5A-7862AA0A60E5
  Boot ID:                    306f36e0-ded3-4b45-946a-89509f845c21
  Kernel Version:             4.15.0-101-generic
  OS Image:                   Ubuntu 18.04.4 LTS
  Operating System:           linux
  Architecture:               amd64
  Container Runtime Version:  docker://19.3.6
  Kubelet Version:            v1.18.8
  Kube-Proxy Version:         v1.18.8
Non-terminated Pods:          (5 in total)
  Namespace                   Name                                    CPU Requests  CPU Limits  Memory Requests  Memory Limits  AGE
  ---------                   ----                                    ------------  ----------  ---------------  -------------  ---
  default                     toleration-demo-dep-54f9ff64b9-7zcrn    0 (0%)        0 (0%)      0 (0%)           0 (0%)         4h9m
  default                     toleration-demo-dep-54f9ff64b9-9sldm    0 (0%)        0 (0%)      0 (0%)           0 (0%)         4h9m
  default                     toleration-demo-dep-54f9ff64b9-rgh7z    0 (0%)        0 (0%)      0 (0%)           0 (0%)         4h9m
  kube-system                 calico-node-2jlhm                       250m (12%)    0 (0%)      0 (0%)           0 (0%)         39d
  kube-system                 kube-proxy-54894                        0 (0%)        0 (0%)      0 (0%)           0 (0%)         22d
Allocated resources:
  (Total limits may be over 100 percent, i.e., overcommitted.)
  Resource           Requests    Limits
  --------           --------    ------
  cpu                250m (12%)  0 (0%)
  memory             0 (0%)      0 (0%)
  ephemeral-storage  0 (0%)      0 (0%)
  hugepages-2Mi      0 (0%)      0 (0%)
Events:              <none>

That's a lot of information. What's important for you?

• Most of the information is informational regarding the system IP, hostname, resources (CPUs, GPUs, memory) and version information (OS, Docker, Kubernetes).
• kubelet service status.
• Unschedulable parameter.
• The Conditions section can indicate whether there are system resource issues that will affect the running of the application. For example, if any of the OutOfDisk, MemoryPressure, or DiskPressure conditions are True, there are insufficient system resources to serve further workloads.
• The Events section at last will also have messages that can indicate if there are issues with the environment.

Hope you like this quick Kubernetes tip. Stay tuned and don't forget to subscribe for more.