WEBVTT 00:00.180 --> 00:03.390 Hello and welcome to this lecture. In this lecture 00:03.390 --> 00:06.410 we will talk about nodes selectors in Kubernetes. 00:06.420 --> 00:09.080 Let us start with a simple example. 00:09.450 --> 00:16.260 You have a three node cluster of which two are smaller nodes with lower hardware resources and one of 00:16.260 --> 00:23.600 them is a larger node configured with higher resources you have different kinds of workloads running 00:23.600 --> 00:24.820 in your cluster. 00:25.010 --> 00:31.490 You would like to dedicate the data processing workloads that require higher horsepower to the larger 00:31.490 --> 00:39.460 node as that is the only node that will not run out of resources in case the job demands extra resources. 00:39.470 --> 00:45.340 However, in the current default setup, any pods can go to any nodes. 00:45.380 --> 00:53.940 So Pod C in this case may very well end up on nodes two or three which is not desired. To solve this 00:53.960 --> 00:59.830 we can set a limitation on the pods so that they only run on particular nodes. 00:59.990 --> 01:02.050 There are two ways to do this. 01:02.060 --> 01:06.750 The first is using Node selectors which is the simple and easier method. 01:06.800 --> 01:13.700 For this we look at the pod definition file we created earlier this file has a simple definition to create 01:13.700 --> 01:20.360 a pod with a data processing image to limit this pod to run on the larger node 01:20.570 --> 01:27.500 We add a new property called Node selector to the spec section and specify the size as large. 01:27.890 --> 01:28.670 But wait a minute. 01:28.760 --> 01:36.050 Where did the size large come from and how does Kubernetes know which is the large node. The key value 01:36.050 --> 01:44.240 pair of size and large are in fact labels assigned to the nodes the scheduler uses these labels to match 01:44.330 --> 01:51.230 and identify the right note to place the pods on labels and selectors are a topic we have seen many 01:51.230 --> 01:58.010 times throughout this Kubernetes course such as with services replica sets and deployments to use 01:58.010 --> 02:00.540 labels in a known selector like this. 02:00.620 --> 02:05.440 You must have first labelled your nodes prior to creating this pod. 02:06.450 --> 02:11.620 So let us go back and see how we can label the nodes to label a node. 02:11.670 --> 02:18.330 Use the command Kube control label nodes followed by the name of the node and the label in a key value 02:18.330 --> 02:19.740 pair format. 02:19.740 --> 02:27.060 In this case it would be Kube control label nodes Node 1 followed by the label in a key value format 02:27.150 --> 02:30.030 such as size equals large. 02:30.030 --> 02:36.690 Now that we have labeled the node we can get back to creating the pod this time with the node selector 02:36.720 --> 02:39.180 set to a size of large. 02:39.180 --> 02:47.970 When the pod is now created it is placed on Node 1 as desired not selectors served our purpose but it 02:47.970 --> 02:49.430 has limitations. 02:49.440 --> 02:53.470 We used a single label and selector to achieve our goal here. 02:53.550 --> 02:56.950 But what if our requirement is much more complex. 02:57.000 --> 03:04.080 For example, we would like to say something like place the pod on a large or medium node or something 03:04.080 --> 03:08.240 like place the pod on any nodes that are not small. 03:08.430 --> 03:16.110 You cannot achieve this using Node selectors for this node affinity and anti affinity features were 03:16.110 --> 03:19.020 introduced and we will look at that next.