A node is a worker machine in Kubernetes, previously known as a minion. A node may be a VM or physical machine, depending on the cluster. A node is where your application containers will run.
Each node contains the services necessary to run pods and is managed by the master components. The services on a node include the container runtime, kubelet and kube-proxy.
To see which nodes are part of your Kubernetes cluster run the
kubectl get nodes command:
kubectl get nodes
---
NAME STATUS ROLES AGE VERSION
minikube Ready master 77d v1.16.0
As we are using minikube we only have a single node. Below is the output of a 3 node cluster:
kubectl get nodes
---
NAME STATUS ROLES AGE VERSION
gke-kbc-steven-default-pool-b82ee1c9-5n9j Ready <none> 20m v1.11.7-gke.4
gke-kbc-steven-default-pool-b82ee1c9-6wnx Ready <none> 20m v1.11.7-gke.4
gke-kbc-steven-default-pool-b82ee1c9-x13z Ready <none> 20m v1.11.7-gke.4
We can use the kubectl get nodes -o wide command to get some additional
information about the nodes:
kubectl get nodes -o wide
---
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
minikube Ready master 77d v1.16.0 10.0.2.15 <none> Buildroot 2018.05 4.15.0 docker://18.9.6
If we want more detailed information about a node we have to use the
kubectl describe nodes <node_name> command, for example:
kubectl describe nodes minikube
---
Name: minikube
Roles: master
Labels: beta.kubernetes.io/arch=amd64
beta.kubernetes.io/os=linux
kubernetes.io/arch=amd64
kubernetes.io/hostname=minikube
kubernetes.io/os=linux
node-role.kubernetes.io/master=
Annotations: kubeadm.alpha.kubernetes.io/cri-socket: /var/run/dockershim.sock
node.alpha.kubernetes.io/ttl: 0
volumes.kubernetes.io/controller-managed-attach-detach: true
CreationTimestamp: Wed, 10 Jul 2019 13:29:48 +0200
Taints: <none>
Unschedulable: false
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
MemoryPressure False Thu, 26 Sep 2019 11:50:39 +0200 Wed, 10 Jul 2019 13:29:43 +0200 KubeletHasSufficientMemory kubelet has sufficient memory available
DiskPressure False Thu, 26 Sep 2019 11:50:39 +0200 Wed, 10 Jul 2019 13:29:43 +0200 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False Thu, 26 Sep 2019 11:50:39 +0200 Wed, 10 Jul 2019 13:29:43 +0200 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True Thu, 26 Sep 2019 11:50:39 +0200 Wed, 10 Jul 2019 13:29:43 +0200 KubeletReady kubelet is posting ready status
Addresses:
InternalIP: 10.0.2.15
Hostname: minikube
Capacity:
cpu: 2
ephemeral-storage: 17784772Ki
hugepages-2Mi: 0
memory: 2038624Ki
pods: 110
Allocatable:
cpu: 2
ephemeral-storage: 16390445849
hugepages-2Mi: 0
memory: 1936224Ki
pods: 110
System Info:
Machine ID: 84a95625dace4d7b8313ea0f131bebd1
System UUID: 2449230B-73F2-456A-B1E8-3A5F61B9B546
Boot ID: 93caae44-301d-4799-8ba7-d5fcf30b2e52
Kernel Version: 4.15.0
OS Image: Buildroot 2018.05
Operating System: linux
Architecture: amd64
Container Runtime Version: docker://18.9.6
Kubelet Version: v1.16.0
Kube-Proxy Version: v1.16.0
Non-terminated Pods: (19 in total)
Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits AGE
--------- ---- ------------ ---------- --------------- ------------- ---
default bigcommerce-extension-9f56dd765-6pvgj 0 (0%) 0 (0%) 0 (0%) 0 (0%) 77d
default container-info-c5cf66fb6-9r4gp 0 (0%) 0 (0%) 0 (0%) 0 (0%) 28d
default container-info-c5cf66fb6-q69fs 0 (0%) 0 (0%) 0 (0%) 0 (0%) 28d
default container-info-c5cf66fb6-zrf6w 0 (0%) 0 (0%) 0 (0%) 0 (0%) 28d
default nginx 0 (0%) 0 (0%) 0 (0%) 0 (0%) 34d
default nginx2 0 (0%) 0 (0%) 0 (0%) 0 (0%) 34d
default nginx3 0 (0%) 0 (0%) 0 (0%) 0 (0%) 34d
kube-system coredns-5644d7b6d9-cmvbm 100m (5%) 0 (0%) 70Mi (3%) 170Mi (8%) 5m46s
kube-system coredns-5644d7b6d9-vbl8f 100m (5%) 0 (0%) 70Mi (3%) 170Mi (8%) 5m47s
kube-system etcd-minikube 0 (0%) 0 (0%) 0 (0%) 0 (0%) 6m11s
kube-system kube-addon-manager-minikube 5m (0%) 0 (0%) 50Mi (2%) 0 (0%) 6m12s
kube-system kube-apiserver-minikube 250m (12%) 0 (0%) 0 (0%) 0 (0%) 6m12s
kube-system kube-controller-manager-minikube 200m (10%) 0 (0%) 0 (0%) 0 (0%) 6m10s
kube-system kube-proxy-mkxhk 0 (0%) 0 (0%) 0 (0%) 0 (0%) 5m40s
kube-system kube-scheduler-minikube 100m (5%) 0 (0%) 0 (0%) 0 (0%) 6m11s
kube-system storage-provisioner 0 (0%) 0 (0%) 0 (0%) 0 (0%) 77d
kubernetes-dashboard dashboard-metrics-scraper-76585494d8-xpxpb 0 (0%) 0 (0%) 0 (0%) 0 (0%) 5m47s
kubernetes-dashboard kubernetes-dashboard-57f4cb4545-n7ct4 0 (0%) 0 (0%) 0 (0%) 0 (0%) 5m47s
lab-04 nginx 0 (0%) 0 (0%) 0 (0%) 0 (0%) 28d
Allocated resources:
(Total limits may be over 100 percent, i.e., overcommitted.)
Resource Requests Limits
-------- -------- ------
cpu 755m (37%) 0 (0%)
memory 190Mi (10%) 340Mi (17%)
ephemeral-storage 0 (0%) 0 (0%)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Starting 6m23s kubelet, minikube Starting kubelet.
Normal NodeHasSufficientMemory 6m22s (x8 over 6m23s) kubelet, minikube Node minikube status is now: NodeHasSufficientMemory
Normal NodeHasNoDiskPressure 6m22s (x8 over 6m23s) kubelet, minikube Node minikube status is now: NodeHasNoDiskPressure
Normal NodeHasSufficientPID 6m22s (x7 over 6m23s) kubelet, minikube Node minikube status is now: NodeHasSufficientPID
Normal NodeAllocatableEnforced 6m22s kubelet, minikube Updated Node Allocatable limit across pods
Normal Starting 6m kube-proxy, minikube Starting kube-proxy.
Normal Starting 5m37s kube-proxy, minikube Starting kube-proxy.
Read through the output above to see all the information that is available about the node.
The kubectl describe nodes <node_name> is a very useful tool when
troubleshooting a node that is failing. Going through the output (especially
the event section) will, in almost all cases, give a good indication why the
node is not behaving as it should.