1 00:00:00,740 --> 00:00:04,880 Hello and welcome to this lecture on labels and selectors. 2 00:00:04,880 --> 00:00:12,790 My name is Mumshad Mannambeth what do we know about labels and selectors already labels and selectors 3 00:00:12,820 --> 00:00:16,040 are a standard method to group things together. 4 00:00:16,120 --> 00:00:19,120 Say you have a set of different species. 5 00:00:19,120 --> 00:00:27,830 A user wants to be able to filter them based on different criteria such as based on their class or kind 6 00:00:28,110 --> 00:00:34,260 if they are domestic or wild or see by their color and not just group. 7 00:00:34,290 --> 00:00:42,510 You want to be able to filter them based on a criteria such as all green animals or with multiple criteria 8 00:00:42,600 --> 00:00:44,260 such as everything green. 9 00:00:44,280 --> 00:00:46,150 That is also a bird. 10 00:00:46,410 --> 00:00:53,400 Whatever that classification maybe you need the ability to group things together and filter them based 11 00:00:53,400 --> 00:01:02,190 on your needs and the best way to do that is with labels. Labels or properties attached to each item. 12 00:01:02,190 --> 00:01:11,210 So you add properties to each item for their class kind and color selectors help you filter these items. 13 00:01:11,210 --> 00:01:18,260 For example when you say class equals mammal we get a list of mammals and when you say color equals 14 00:01:18,260 --> 00:01:26,310 green we get the green mammals we see labels and selectors used everywhere such as the keywords you 15 00:01:26,310 --> 00:01:34,340 tag to YouTube videos or blogs that help users filter and find the right content we see labels added 16 00:01:34,340 --> 00:01:41,590 to items in an online store that help you add different kinds of filters to view your products. 17 00:01:41,610 --> 00:01:45,420 So how are labels and selectors used in Kubernetes? 18 00:01:45,480 --> 00:01:53,550 We have created a lot of different types of Objects in Kuberentes. Pods, Services, ReplicaSets and Deployments. 19 00:01:53,550 --> 00:01:58,750 etc. For Kubernetes, all of these are different objects. 20 00:01:58,860 --> 00:02:04,980 Over time you may end up having hundreds or thousands of these objects in your cluster. 21 00:02:04,980 --> 00:02:12,360 Then you will need a way to filter and view different objects by different categories such as to group 22 00:02:12,450 --> 00:02:22,200 objects by their type or view objects by application or by their functionality whatever it may be. 23 00:02:22,260 --> 00:02:31,190 You can group and select objects using labels and selectors for each object attach labels as per your 24 00:02:31,190 --> 00:02:34,300 needs, like app, function etc. 25 00:02:37,270 --> 00:02:42,350 Then while selecting specify a condition to filter specific objects. 26 00:02:42,490 --> 00:02:50,170 For example app == App1. So how exactly do you specify labels in kubernetes. 27 00:02:51,070 --> 00:02:54,070 In a pod-definition file, under metadata, 28 00:02:54,110 --> 00:03:01,110 create a section called labels. Under that add the labels in a key value format like this. 29 00:03:01,310 --> 00:03:09,800 You can add as many labels as you like. Once the pod is created, to select the pod with the labels 30 00:03:09,850 --> 00:03:16,540 use the kubectl get pods command along with the selector option, and specify the condition like 31 00:03:16,690 --> 00:03:20,860 app=App1. 32 00:03:20,920 --> 00:03:27,930 Now this is one use case of labels and selectors. Kubernetes objects use labels and selectors internally 33 00:03:28,290 --> 00:03:34,680 to connect different objects together. For example to create a replicaset consisting of 3 different 34 00:03:34,680 --> 00:03:35,610 pods, 35 00:03:35,610 --> 00:03:43,080 we first label the pod definition and use selector in a replicaset to group the pods . In the replica-set 36 00:03:43,080 --> 00:03:44,820 set definition file. 37 00:03:44,820 --> 00:03:48,240 You will see labels defined in two places. 38 00:03:48,240 --> 00:03:52,620 Note that this is an area where beginners attempt to make a mistake. 39 00:03:52,740 --> 00:03:59,250 The labels defined under the template section are the labels configured on the pods. The labels you see 40 00:03:59,250 --> 00:04:03,910 at the top are the labels of the replicas set itself. 41 00:04:03,900 --> 00:04:09,870 We're not really concerned about the labels of the replica set for now because we are trying to get 42 00:04:09,870 --> 00:04:12,940 the replica set to discover the pods. 43 00:04:13,050 --> 00:04:18,960 The labels on the replica set will be used if you were to configure some other object to discover the 44 00:04:18,960 --> 00:04:26,250 replica set in order to connect the replica set to the pod we configure the selector field under the 45 00:04:26,250 --> 00:04:34,230 replica set specification to match the labels defined on the pod a single label will do if it matches 46 00:04:34,230 --> 00:04:35,230 correctly. 47 00:04:35,250 --> 00:04:40,950 However if you feel there could be other pods with the same label but with a different function then 48 00:04:40,950 --> 00:04:48,670 you could specify both the labels to ensure that the right pods are discovered by the replica set on 49 00:04:48,670 --> 00:04:49,420 creation. 50 00:04:49,420 --> 00:04:56,970 If the labels match the replica set is created successfully it works the same for other objects like 51 00:04:56,970 --> 00:05:04,200 a service when a service is created it uses the selector defined in the service definition file to match 52 00:05:04,230 --> 00:05:09,130 the labels set on the pods in the replica set definition file. 53 00:05:09,150 --> 00:05:17,820 Finally let’s look at annotations. While labels and selectors are used to group and select objects, annotations 54 00:05:17,820 --> 00:05:21,960 are used to record other details for inflammatory purpose. 55 00:05:22,080 --> 00:05:30,570 For example tool details like name, version build information etc or contact details, phone numbers, email 56 00:05:30,570 --> 00:05:38,840 ids etc, that may be used for some kind of integration purpose. Well, that’s it for this lecture on 57 00:05:38,840 --> 00:05:41,320 labels and selectors and annotations. 58 00:05:41,360 --> 00:05:46,580 Head over to the coding exercises section and practice working with labels and selectors.