1 00:00:00,180 --> 00:00:03,390 Hello and welcome to this lecture. In this lecture 2 00:00:03,390 --> 00:00:06,410 we will talk about nodes selectors in Kubernetes. 3 00:00:06,420 --> 00:00:09,080 Let us start with a simple example. 4 00:00:09,450 --> 00:00:16,260 You have a three node cluster of which two are smaller nodes with lower hardware resources and one of 5 00:00:16,260 --> 00:00:23,600 them is a larger node configured with higher resources you have different kinds of workloads running 6 00:00:23,600 --> 00:00:24,820 in your cluster. 7 00:00:25,010 --> 00:00:31,490 You would like to dedicate the data processing workloads that require higher horsepower to the larger 8 00:00:31,490 --> 00:00:39,460 node as that is the only node that will not run out of resources in case the job demands extra resources. 9 00:00:39,470 --> 00:00:45,340 However, in the current default setup, any pods can go to any nodes. 10 00:00:45,380 --> 00:00:53,940 So Pod C in this case may very well end up on nodes two or three which is not desired. To solve this 11 00:00:53,960 --> 00:00:59,830 we can set a limitation on the pods so that they only run on particular nodes. 12 00:00:59,990 --> 00:01:02,050 There are two ways to do this. 13 00:01:02,060 --> 00:01:06,750 The first is using Node selectors which is the simple and easier method. 14 00:01:06,800 --> 00:01:13,700 For this we look at the pod definition file we created earlier this file has a simple definition to create 15 00:01:13,700 --> 00:01:20,360 a pod with a data processing image to limit this pod to run on the larger node 16 00:01:20,570 --> 00:01:27,500 We add a new property called Node selector to the spec section and specify the size as large. 17 00:01:27,890 --> 00:01:28,670 But wait a minute. 18 00:01:28,760 --> 00:01:36,050 Where did the size large come from and how does Kubernetes know which is the large node. The key value 19 00:01:36,050 --> 00:01:44,240 pair of size and large are in fact labels assigned to the nodes the scheduler uses these labels to match 20 00:01:44,330 --> 00:01:51,230 and identify the right note to place the pods on labels and selectors are a topic we have seen many 21 00:01:51,230 --> 00:01:58,010 times throughout this Kubernetes course such as with services replica sets and deployments to use 22 00:01:58,010 --> 00:02:00,540 labels in a known selector like this. 23 00:02:00,620 --> 00:02:05,440 You must have first labelled your nodes prior to creating this pod. 24 00:02:06,450 --> 00:02:11,620 So let us go back and see how we can label the nodes to label a node. 25 00:02:11,670 --> 00:02:18,330 Use the command Kube control label nodes followed by the name of the node and the label in a key value 26 00:02:18,330 --> 00:02:19,740 pair format. 27 00:02:19,740 --> 00:02:27,060 In this case it would be Kube control label nodes Node 1 followed by the label in a key value format 28 00:02:27,150 --> 00:02:30,030 such as size equals large. 29 00:02:30,030 --> 00:02:36,690 Now that we have labeled the node we can get back to creating the pod this time with the node selector 30 00:02:36,720 --> 00:02:39,180 set to a size of large. 31 00:02:39,180 --> 00:02:47,970 When the pod is now created it is placed on Node 1 as desired not selectors served our purpose but it 32 00:02:47,970 --> 00:02:49,430 has limitations. 33 00:02:49,440 --> 00:02:53,470 We used a single label and selector to achieve our goal here. 34 00:02:53,550 --> 00:02:56,950 But what if our requirement is much more complex. 35 00:02:57,000 --> 00:03:04,080 For example, we would like to say something like place the pod on a large or medium node or something 36 00:03:04,080 --> 00:03:08,240 like place the pod on any nodes that are not small. 37 00:03:08,430 --> 00:03:16,110 You cannot achieve this using Node selectors for this node affinity and anti affinity features were 38 00:03:16,110 --> 00:03:19,020 introduced and we will look at that next.