1

00:00:00,580 --> 00:00:06,640

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



2

00:00:06,670 --> 00:00:13,700

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



3

00:00:13,700 --> 00:00:20,950

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



4

00:00:21,020 --> 00:00:23,780

So how exactly does a scheduler work in the backend.



5

00:00:24,440 --> 00:00:27,230

Let's start with a simple pod definition file.



6

00:00:27,560 --> 00:00:33,860

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



7

00:00:33,860 --> 00:00:41,600

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



8

00:00:41,600 --> 00:00:48,560

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



9

00:00:48,560 --> 00:00:51,460

Those are the candidates for scheduling.



10

00:00:51,530 --> 00:00:57,020

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



11

00:00:57,020 --> 00:01:03,680

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



12

00:01:03,680 --> 00:01:12,240

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



13

00:01:12,330 --> 00:01:15,780

The pods continue to be in a pending state.



14

00:01:15,780 --> 00:01:17,270

So what can you do about it.



15

00:01:17,280 --> 00:01:23,340

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



16

00:01:23,340 --> 00:01:29,640

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



17

00:01:29,640 --> 00:01:33,540

pod specification while creating the POD.



18

00:01:33,540 --> 00:01:40,610

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



19

00:01:40,710 --> 00:01:46,500

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



20

00:01:46,500 --> 00:01:50,220

you to modify the node Name property of a pod.



21

00:01:50,370 --> 00:01:57,960

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



22

00:01:57,960 --> 00:02:05,910

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



23

00:02:06,000 --> 00:02:13,740

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



24

00:02:13,830 --> 00:02:17,580

set to the binding object in a JSON format.



25

00:02:17,580 --> 00:02:22,850

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



26

00:02:22,920 --> 00:02:24,960

Well that's it for this lecture.



27

00:02:24,960 --> 00:02:30,300

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