WEBVTT

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Hello and welcome to this lecture. In this lecture we look at the different ways of manually scheduling

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a POD on a node. What do you do when you do not have a scheduler in your cluster?

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You, probably do not want to rely on the built in scheduler and instead want to schedule the PODs yourself.

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So how exactly does a scheduler work in the backend.

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Let's start with a simple pod definition file.

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Every POD has a field called NodeName that, by default, is not set.

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You don’t typically specify this field when you create the manifest file, Kubernetes adds it automtically.

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The scheduler goes through all the pods and looks for those that do not have this property set.

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Those are the candidates for scheduling.

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It then identifies the right node for the POD, by running the scheduling algorithm.

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Once identified it schedules the POD on the Node by setting the node Name property to the name of the

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node by creating a binding object. So if there is no scheduler to monitor and schedule nodes what happens?

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The pods continue to be in a pending state.

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So what can you do about it.

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You can manually assign pods to node yourself. Well without a scheduler,

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the easiest way to schedule a pod is to simply set the node name field to the name of the node in your

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pod specification while creating the POD.

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The pod then gets assigned to the specified node. You can only specify the node name at creation time.

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What if the pod is already created and you want to assign the pod to a node? Kubernetes won’t allow

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you to modify the node Name property of a pod.

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So another way to assign a note to an existing pod is to create a binding object and send a post request

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to the pod binding API thus mimicking what the actual scheduler does. In the binding object you specify

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a target node with the name of the node. Then send a post request to the pods binding API with the data

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set to the binding object in a JSON format.

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So you must convert the YAML file into its equivalent JSON format.

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Well that's it for this lecture.

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Head over to the practice test and practice manually scheduling pods on nodes.