WEBVTT 00:04.180 --> 00:07.150 Hello and welcome to this lecture in this lecture. 00:07.180 --> 00:10.000 we will talk about Kube Scheduler. 00:10.000 --> 00:15.540 Earlier we discussed that the kubernetes scheduler is responsible for scheduling pods on nodes. 00:16.300 --> 00:18.640 Now don't let the graphic mislead you. 00:18.670 --> 00:26.710 remember the scheduler is only responsible for deciding which pod goes on which node. It doesn’t actually 00:26.710 --> 00:29.010 place the pod on the nodes. 00:29.050 --> 00:34.690 That’s the job of the kubelet. The kubelet or the captain on the ship is who creates the pod on the 00:34.690 --> 00:35.610 ships. 00:35.610 --> 00:39.860 The scheduler only decides which pod goes where. 00:40.000 --> 00:43.270 Let's look at how the scheduler does that in a bit more detail. 00:43.420 --> 00:48.770 First of all why do you need a scheduler? When there are many ships and many containers, 00:48.940 --> 00:53.450 You want to make sure that the right container ends up on the right ship. 00:53.590 --> 00:57.670 For example there could be different sizes of ships and containers. 00:57.670 --> 01:04.130 You want to make sure the ship has sufficient capacity to accommodate those containers different ships 01:04.150 --> 01:06.280 maybe going to different destinations. 01:06.280 --> 01:11.740 You want to make sure your containers are placed on the right ships so they end up in the right destination 01:12.540 --> 01:17.170 In kubernetes, the scheduler decides which nodes the pods are placed on 01:17.170 --> 01:22.660 depending on certain criteria. You may have PODs with different resource requirements, 01:22.720 --> 01:27.180 You can have nodes in the cluster dedicated to certain applications. 01:27.280 --> 01:33.700 So how does the scheduler assign these PODs? The scheduler looks at each POD and tries to find the 01:33.700 --> 01:35.280 best node for it. 01:35.290 --> 01:37.560 For example, let’s take one of these PODs. 01:37.810 --> 01:41.970 The big blue one. It has a set of CPU and Memory requirements. 01:42.040 --> 01:47.980 The scheduler goes through two phases to identify the best node for the pod in the first phase. 01:48.010 --> 01:52.940 The scheduler tries to filter out the nodes that do not fit the profile for this pod. 01:53.050 --> 01:59.830 For example, the nodes that do not have sufficient CPU and memory resources requested by the pod. 01:59.860 --> 02:06.100 So the first two small nodes are filtered out. So we are now left with two nodes on which the POD 02:06.130 --> 02:07.870 can be placed. 02:07.900 --> 02:14.660 Now how does the scheduler pick one from the two the scheduler ranks the node to identify the best fit 02:14.660 --> 02:15.580 for the pod. 02:15.620 --> 02:21.240 It uses a priority function to assign a score to the nodes on a scale of 0 to 10. 02:21.260 --> 02:28.130 For example the scheduler calculates the amount of resources that would be free on the nodes after placing 02:28.130 --> 02:29.570 the pod on them. 02:29.570 --> 02:36.230 In this case, the one on the right would have 6 CPUs free if the pod was placed on it which is 4 more 02:36.560 --> 02:39.430 than the other one so it gets a better rank. 02:39.530 --> 02:40.820 And so it wins. 02:40.910 --> 02:43.220 So that's how a scheduler works at a high level. 02:43.280 --> 02:48.380 And of course these can be customized and you can write your own scheduler as well. 02:48.380 --> 02:53.660 There are many more topics to look at such as resource requirements, limits, taints and tolerations, 02:53.690 --> 03:00.290 node selectors, affinity rules etc. Which is why we have an entire section dedicated to scheduling coming 03:00.290 --> 03:04.940 up in this course where we will discuss each of these in much more detail. 03:04.940 --> 03:10.040 For now we will continue to focus on the scheduler as a process at a high level. 03:10.760 --> 03:13.160 So how do you install the kube-scheduler? 03:13.160 --> 03:18.740 Download the kube-scheduler from the kubernetes release page. Extract it and run it as a service. 03:19.220 --> 03:20.600 when you run it as a service. 03:20.600 --> 03:23.090 You specify the scheduler configuration file. 03:23.570 --> 03:26.240 So how do you view the kube-scheduler server options? 03:26.240 --> 03:31.820 Again, if you set it up with kubeadm tool, kubeadm deploys the kube-scheduler as a pod 03:31.820 --> 03:33.450 in the kube-system namespace 03:33.470 --> 03:39.030 on the master node. You can see the options within the pod definition file located at etc 03:39.090 --> 03:41.270 kubernetes manifests folder. 03:41.420 --> 03:46.280 You can also see the running process and the effective options by listing the process on the master 03:46.280 --> 03:49.250 node and searching for kube-scheduler. 03:49.250 --> 03:51.020 Well that's it for this lecture. 03:51.200 --> 03:52.550 I will see you in the next.