In Kubernetes, nodes are the (virtual) machines where your workloads in shape of pods run. As a developer you typically don’t deal with nodes directly, however as an admin you might want to familiarize yourself with node operations.
To list available nodes in your cluster (note that the output will depend on the environment you’re using. This example is using the OpenShift Playground):
kubectl get nodes
NAME STATUS ROLES AGE VERSION
crc-rk2fc-master-0 Ready master,worker 102d v1.14.6+888f9c630
One interesting task, from a developer point of view, is to make Kubernetes schedule a pod on a certain node. For this, we first need to label the node we want to target:
kubectl label nodes crc-rk2fc-master-0 shouldrun=here
node/crc-rk2fc-master-0 labeled
Now we can create a pod
that gets scheduled on the node with the label shouldrun=here:
kubectl apply -f https://raw.githubusercontent.com/openshift-evangelists/kbe/main/specs/nodes/pod.yaml
kubectl get pods --output=wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
onspecificnode 1/1 Running 0 2m31s 10.128.1.11 crc-rk2fc-master-0 <none> <none>
To learn more about a specific node, crc-rk2fc-master-0 in our case, do:
kubectl describe node crc-rk2fc-master-0
Name: crc-rk2fc-master-0
Roles: master,worker
Labels: beta.kubernetes.io/arch=amd64
beta.kubernetes.io/os=linux
kubernetes.io/arch=amd64
kubernetes.io/hostname=crc-rk2fc-master-0
kubernetes.io/os=linux
node-role.kubernetes.io/master=
node-role.kubernetes.io/worker=
node.openshift.io/os_id=rhcos
shouldrun=here
Annotations: machine.openshift.io/machine: openshift-machine-api/crc-rk2fc-master-0
machineconfiguration.openshift.io/currentConfig: rendered-master-757d2d73a4ba859a3508c78070169043
machineconfiguration.openshift.io/desiredConfig: rendered-master-757d2d73a4ba859a3508c78070169043
machineconfiguration.openshift.io/reason:
machineconfiguration.openshift.io/ssh: accessed
machineconfiguration.openshift.io/state: Done
volumes.kubernetes.io/controller-managed-attach-detach: true
CreationTimestamp: Thu, 12 Dec 2019 06:47:09 +0000
Taints: <none>
Unschedulable: false
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
MemoryPressure False Mon, 23 Mar 2020 18:20:39 +0000 Thu, 12 Dec 2019 06:47:08 +0000 KubeletHasSufficientMemory kubelet has sufficient memoryavailable
DiskPressure False Mon, 23 Mar 2020 18:20:39 +0000 Thu, 12 Dec 2019 06:47:08 +0000 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False Mon, 23 Mar 2020 18:20:39 +0000 Thu, 12 Dec 2019 06:47:08 +0000 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True Mon, 23 Mar 2020 18:20:39 +0000 Mon, 23 Mar 2020 17:56:48 +0000 KubeletReady kubelet is posting ready status
Addresses:
InternalIP: 172.17.0.23
Hostname: crc-rk2fc-master-0
Capacity:
cpu: 6
hugepages-1Gi: 0
hugepages-2Mi: 0
memory: 16033876Ki
pods: 250
Allocatable:
cpu: 5500m
hugepages-1Gi: 0
hugepages-2Mi: 0
memory: 15419476Ki
pods: 250
System Info:
Machine ID: 33c8de1eb5364c94b5e215e58eef30ac
System UUID: 33c8de1eb5364c94b5e215e58eef30ac
Boot ID: f51f55d7-7702-48bc-bbc0-d68372e0fbf1
Kernel Version: 4.18.0-147.0.3.el8_1.x86_64
OS Image: Red Hat Enterprise Linux CoreOS 42.81.20191203.0 (Ootpa)
Operating System: linux
Architecture: amd64
Container Runtime Version: cri-o://1.14.11-0.24.dev.rhaos4.2.gitc41de67.el8
Kubelet Version: v1.14.6+888f9c630
Kube-Proxy Version: v1.14.6+888f9c630
Non-terminated Pods: (46 in total)
Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits AGE
--------- ---- ------------ ---------- --------------- ------------- ---
default onspecificnode 0 (0%) 0 (0%) 0 (0%) 0 (0%) 3m2s
openshift-apiserver
...
Allocated resources:
(Total limits may be over 100 percent, i.e., overcommitted.)
Resource Requests Limits
-------- -------- ------
cpu 3010m (54%) 700m (12%)
memory 8289Mi (55%) 687Mi (4%)
ephemeral-storage 0 (0%) 0 (0%)
Note that there are more sophisticated methods than shown above, such as using affinity, to assign pods to nodes and depending on your use case, you might want to check those out as well.