1 00:00:02,040 --> 00:00:04,030 So where's this error coming from? 2 00:00:04,030 --> 00:00:06,820 What's this missing selector thing? 3 00:00:06,820 --> 00:00:11,800 Well, we fix it by going to the specification 4 00:00:11,800 --> 00:00:13,690 of our deployment 5 00:00:13,690 --> 00:00:16,360 so not the specification of the pod 6 00:00:16,360 --> 00:00:18,700 but the specification of the deployment. 7 00:00:18,700 --> 00:00:21,770 And besides specifying the number of replicas 8 00:00:21,770 --> 00:00:23,930 and our pods template here, 9 00:00:23,930 --> 00:00:28,010 we also must add a selector key here. 10 00:00:28,010 --> 00:00:30,996 And on this selector key nested below it 11 00:00:30,996 --> 00:00:34,750 we can add a match labels key, 12 00:00:34,750 --> 00:00:35,961 and then nested below that 13 00:00:35,961 --> 00:00:40,770 a key/value pair of the pod labels 14 00:00:40,770 --> 00:00:43,053 we wanna match with this deployment. 15 00:00:44,120 --> 00:00:45,520 Okay, that sounds very triptych. 16 00:00:45,520 --> 00:00:47,270 What does this mean? 17 00:00:47,270 --> 00:00:48,103 Well, 18 00:00:48,103 --> 00:00:50,940 we got a template here for this deployment 19 00:00:50,940 --> 00:00:52,840 and therefore it should be obvious 20 00:00:52,840 --> 00:00:56,080 which pods are created by this deployment. 21 00:00:56,080 --> 00:00:57,450 And it kind of is. 22 00:00:57,450 --> 00:00:59,973 The pod defined in this template will be created 23 00:00:59,973 --> 00:01:02,443 when this deployment is applied. 24 00:01:03,630 --> 00:01:08,020 But deployments are dynamic objects or dynamic things 25 00:01:08,020 --> 00:01:09,610 in the Kubernetes world. 26 00:01:09,610 --> 00:01:10,443 For example, 27 00:01:10,443 --> 00:01:12,990 if you scale up the number of pods 28 00:01:12,990 --> 00:01:15,650 after a deployment has been created, 29 00:01:15,650 --> 00:01:17,959 these new pods which are created 30 00:01:17,959 --> 00:01:20,810 will still automatically be managed 31 00:01:20,810 --> 00:01:23,133 by the already existing deployment. 32 00:01:24,140 --> 00:01:28,450 So a deployment continuously watches all the pods 33 00:01:28,450 --> 00:01:29,800 which are out there 34 00:01:29,800 --> 00:01:34,140 and sees if there are any pods it should control. 35 00:01:34,140 --> 00:01:37,550 And it selects the to be controlled pods 36 00:01:37,550 --> 00:01:39,690 with a so-called selector. 37 00:01:39,690 --> 00:01:41,320 And you will see selectors 38 00:01:41,320 --> 00:01:45,020 on pretty much all resources Kubernetes works with. 39 00:01:45,020 --> 00:01:48,040 For example, Azure Services. 40 00:01:48,040 --> 00:01:50,410 Now there are different types of selectors 41 00:01:50,410 --> 00:01:51,940 here for a deployment 42 00:01:51,940 --> 00:01:55,190 we can use two different kinds of selecting. 43 00:01:55,190 --> 00:01:59,690 We can match labels and we can match expressions. 44 00:01:59,690 --> 00:02:02,930 Now expressions are more complex selectors 45 00:02:02,930 --> 00:02:05,430 so we'll not have a look at them right now 46 00:02:05,430 --> 00:02:07,900 instead we'll match labels. 47 00:02:07,900 --> 00:02:11,910 And then nested below that you simply have key/value pairs 48 00:02:11,910 --> 00:02:16,110 of labels on the pods which should be controlled 49 00:02:16,110 --> 00:02:17,643 by that deployment. 50 00:02:18,560 --> 00:02:21,720 So in this case, we are trading these pots 51 00:02:21,720 --> 00:02:23,960 which have this label on it. 52 00:02:23,960 --> 00:02:24,793 And by the way, 53 00:02:24,793 --> 00:02:27,580 they could have multiple labels. 54 00:02:27,580 --> 00:02:30,940 Which as mentioned before are totally up to you. 55 00:02:30,940 --> 00:02:34,163 Both the key and the value are up to you. 56 00:02:35,350 --> 00:02:38,160 But you can have one or more labels 57 00:02:38,160 --> 00:02:41,160 on a given object in this case on a pod. 58 00:02:41,160 --> 00:02:44,590 And then you can connect that to another object 59 00:02:44,590 --> 00:02:45,423 in this case, 60 00:02:45,423 --> 00:02:48,320 to the deployment with a so-called selector 61 00:02:48,320 --> 00:02:51,240 so that this deployment knows which pods 62 00:02:51,240 --> 00:02:52,991 which are out there running in the cluster 63 00:02:52,991 --> 00:02:55,073 should be controlled by it. 64 00:02:55,950 --> 00:02:59,600 And you then simply add the key/value pairs of the pods 65 00:02:59,600 --> 00:03:02,850 that should be controlled below match labels here. 66 00:03:02,850 --> 00:03:05,003 So for example like this, 67 00:03:07,020 --> 00:03:10,400 now I would tell this deployment 68 00:03:10,400 --> 00:03:13,930 that all the pods which have a label of app 69 00:03:13,930 --> 00:03:16,040 with a value of second app, 70 00:03:16,040 --> 00:03:19,060 and which have a label with a name of tier 71 00:03:19,060 --> 00:03:20,720 with a value of backend, 72 00:03:20,720 --> 00:03:23,395 should be controlled by this deployment. 73 00:03:23,395 --> 00:03:26,610 Other pods which only have app, 74 00:03:26,610 --> 00:03:27,490 second app, 75 00:03:27,490 --> 00:03:29,140 but not this tier 76 00:03:29,140 --> 00:03:31,350 or which have a different app label 77 00:03:31,350 --> 00:03:34,840 or which don't have the app and tier label at all 78 00:03:34,840 --> 00:03:38,640 will not be controlled by this deployment. 79 00:03:38,640 --> 00:03:40,340 I hope this makes sense. 80 00:03:40,340 --> 00:03:41,640 It tells the deployment 81 00:03:41,640 --> 00:03:44,323 which pods belong to it so to say. 82 00:03:45,290 --> 00:03:49,360 And we'll see this again, when we later work on a service. 83 00:03:49,360 --> 00:03:52,280 So for the moment let's save this updated file 84 00:03:52,280 --> 00:03:55,173 and let's now try applying this file again. 85 00:03:56,080 --> 00:03:57,500 And this now looks better. 86 00:03:57,500 --> 00:03:58,333 Now, you'll see 87 00:03:58,333 --> 00:04:00,140 this deployment was created. 88 00:04:00,140 --> 00:04:00,973 And therefore, 89 00:04:00,973 --> 00:04:01,806 if you run, 90 00:04:01,806 --> 00:04:03,550 get deployments here, 91 00:04:03,550 --> 00:04:06,643 you see that deployment up and running. 92 00:04:07,980 --> 00:04:11,270 And of course, if we now call get pods, 93 00:04:11,270 --> 00:04:13,400 we also see this up and running, 94 00:04:13,400 --> 00:04:15,740 but now we didn't have to enter a command 95 00:04:15,740 --> 00:04:17,000 in the command line 96 00:04:17,000 --> 00:04:19,290 except for the apply command of course. 97 00:04:19,290 --> 00:04:20,123 But instead, 98 00:04:20,123 --> 00:04:24,910 all our configuration is encoded here in this conflict file. 99 00:04:26,850 --> 00:04:28,950 Now at the moment we can't visit the app 100 00:04:28,950 --> 00:04:30,740 because a services missing 101 00:04:30,740 --> 00:04:32,930 but this is a huge step forward 102 00:04:32,930 --> 00:04:36,950 since we now know about this declarative approach. 103 00:04:36,950 --> 00:04:41,093 Let's now see how we can also declare a service resource.