What happens when you run kubectl apply
Kubernetes cluster: the control plane decides, the nodes run your app
A Kubernetes cluster is a group of servers. They do not all do the same job. Some of them never run a single line of your app.
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Here, Kubernetes has 5 servers to work with.
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Together, those servers form a cluster. They are not equal: one of them decides, and the 4 others do the work.
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The 4 workers are the worker nodes, or simply nodes. A node runs containers: today those of other apps, and soon yours, wherever there is room.
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The fifth server runs the control plane, the part of Kubernetes that decides which node runs what and keeps track of it all. Here it is one server; real clusters run it on several, for the same Sunday reason.
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The control plane is ready to decide, but it cannot guess your wish. How do you tell it, and how much do you have to explain?
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Quick check
One Sunday, the server of the control plane stops.
Show the answer
No. The nodes keep running the containers they have. But nothing new can be added until the control plane is back.
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Go further
Two more names, for the servers of a cluster.