Deploying a k8s cluster
You can use a cloud provider, deploying on bare-metal quite hard, other good alternatives.
http://kind.sigs.k8s.io that has a really cool logo, and works on using containers for the nodes.
Go check the pages of cloud providers on how to deploy it there since it will change depending on the provider.
One thing to bare in mind is that in order to use kubectl with your cluster
you need a ~/.kube/config file, probably your cloud provider will give that
to you.
Also you can go to k8s cheatsheet (describe cluster) to see the basics commands on describing a cluster.
I will just cover some of the commands here, like
k describe nodes <node name>
At the top you can see basic node info:
Name: kind-control-plane
Roles: control-plane
Labels: beta.kubernetes.io/arch=arm64
beta.kubernetes.io/os=linux
kubernetes.io/arch=arm64
We can see that it is linux on ARM
Next we can see info about the operation of the node
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
MemoryPressure False 29 Apr 2024 29 Apr 2024 KubeletHasSufficientMemory kubelet has sufficient memory available
DiskPressure False 29 Apr 2024 29 Apr 2024 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False 29 Apr 2024 29 Apr 2024 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True 29 Apr 2024 29 Apr 2024 KubeletReady kubelet is posting ready status
Here we can see that the node is Ready, that it has sufficient memory, it has no disk pressure, and that is has sufficient PID.
Then we see info about the capacity of the system.
Capacity:
cpu: 1
memory: 1933908Ki
pods: 110
Allocatable:
cpu: 1
memory: 1933908Ki
pods: 110
Then info about software in the node like OS image, docker version all that.
System Info:
# more stuff
Kernel Version: 6.5.6-200.fc38.aarch64
OS Image: Debian GNU/Linux 12 (bookworm)
Operating System: linux
Architecture: arm64
Container Runtime Version: containerd://1.7.13
Kubelet Version: v1.29.2
Kube-Proxy Version: v1.29.2
Then info about the pods running on the node:
Non-terminated Pods: (9 in total)
Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits Age
--------- ---- ------------ ---------- --------------- ------------- ---
kube-system coredns-76f75df574-92286 100m (10%) 0 (0%) 70Mi (3%) 170Mi (9%) 23s
kube-system coredns-76f75df574-m2z2k 100m (10%) 0 (0%) 70Mi (3%) 170Mi (9%) 23s
kube-system etcd-kind-control-plane 100m (10%) 0 (0%) 100Mi (5%) 0 (0%) 39s
kube-system kindnet-qm29d 100m (10%) 100m (10%) 50Mi (2%) 50Mi (2%) 23s
kube-system kube-apiserver-kind-control-plane 250m (25%) 0 (0%) 0 (0%) 0 (0%) 39s
# more stuff
We can see that k8s tracks both requests and upper limits for resource for
each Pod. The difference is that resources requested by a pod are guaranteed to
be present in the node, while pod's limit is the max amount of given resource
that pod can consume
Cluster Components
Many components that make up the k8s cluster are actually deployed using k8s itself. All of them run in the kube-system namespace
-
k8s proxy
It routes network traffic to load-balanced services in the k8s cluster. It must be present on every node in the cluster
% k get daemonSets --namespace=kube-system kube-proxy -
k8s dns
provides naming and discover for the services that are defined in the cluster
% k get deployments --namespace=kube-system coredns