WEBVTT 00:00.960 --> 00:01.793 -: In the last section, 00:01.793 --> 00:03.600 we spoke about what a volume is, 00:03.600 --> 00:05.790 compared to a persistent volume. 00:05.790 --> 00:07.290 We're now going to pivot a little bit 00:07.290 --> 00:09.450 and talk about how a persistent volume claim 00:09.450 --> 00:11.550 compares to a persistent volume. 00:11.550 --> 00:13.140 Now, these two topics right here, 00:13.140 --> 00:14.640 and their relation with each other 00:14.640 --> 00:17.370 is kind of hard to understand at first glance. 00:17.370 --> 00:19.680 So I'm gonna give you a very quick analogy 00:19.680 --> 00:20.880 or a very quick story 00:20.880 --> 00:22.290 to help you understand what the difference 00:22.290 --> 00:25.680 is between a volume claim and a persistent volume. 00:25.680 --> 00:27.240 After I give you the analogy, 00:27.240 --> 00:29.067 we'll then kind of take this little short story 00:29.067 --> 00:31.800 and pivot it over to the world of Kubernetes 00:31.800 --> 00:34.260 and apply some real terminology to it. 00:34.260 --> 00:35.820 So in this section, let's get to it. 00:35.820 --> 00:38.280 We're gonna look at a very quick little short story 00:38.280 --> 00:39.540 to help you understand the difference 00:39.540 --> 00:42.933 between a persistent volume and a persistent volume claim. 00:44.010 --> 00:45.570 So here's my short story. 00:45.570 --> 00:48.870 I want you to imagine that you are walking down a sidewalk, 00:48.870 --> 00:50.250 and you are in the process 00:50.250 --> 00:53.040 of building out some custom computer. 00:53.040 --> 00:55.080 You are building a computer from scratch, 00:55.080 --> 00:57.570 and so maybe at this point in time you have a case, 00:57.570 --> 01:00.720 and a motherboard, and a processor, some RAM 01:00.720 --> 01:01.980 and a Graphics Cards. 01:01.980 --> 01:03.360 And the last thing that you need 01:03.360 --> 01:05.700 might be some type of hard drive. 01:05.700 --> 01:08.250 So you're walking along with your custom PC 01:08.250 --> 01:10.657 and you see a big billboard that says, 01:10.657 --> 01:12.630 "Come on down to the computer store, 01:12.630 --> 01:15.810 we have two really great hard drives that are available. 01:15.810 --> 01:20.070 We have a 500 GB option and a 1 TB option." 01:20.070 --> 01:22.387 So you look at this billboard right here and you say, 01:22.387 --> 01:24.420 "You know what, between these two options, 01:24.420 --> 01:26.910 I think that 500 GB hard drive 01:26.910 --> 01:30.450 would be perfect for my custom computer." 01:30.450 --> 01:32.310 So you take your custom computer, 01:32.310 --> 01:34.500 you continue walking down the sidewalk 01:34.500 --> 01:36.573 until you get to the computer store. 01:38.190 --> 01:39.450 Now at the computer store, 01:39.450 --> 01:41.437 you talk to a salesperson and you say, 01:41.437 --> 01:43.350 "Hey, you know I just saw that billboard 01:43.350 --> 01:46.230 where you were advertising the 500 GB option. 01:46.230 --> 01:49.020 I would love to have one of those hard drives." 01:49.020 --> 01:51.000 So the salesperson says, "Not a problem." 01:51.000 --> 01:53.850 And they turn around and they go to some store room 01:53.850 --> 01:57.153 or some like inventory store, inside the computer store, 01:57.153 --> 01:59.550 and they look through all the different pieces 01:59.550 --> 02:02.061 of hardware that they have available. 02:02.061 --> 02:04.530 Now, you had asked for a 500 GB hard drive, 02:04.530 --> 02:07.500 so the salesperson says, "Great, this is perfect. 02:07.500 --> 02:09.582 I can meet your request right now, 02:09.582 --> 02:13.020 I've got a 500 GB hard drive, ready to go." 02:13.020 --> 02:15.210 And so they throw that thing over to you 02:15.210 --> 02:18.150 and you now have a 500 GB hard drive 02:18.150 --> 02:21.000 that you can put into your computer. 02:21.000 --> 02:23.100 All right, so that's the entire short story. 02:23.100 --> 02:25.020 That's kind of scenario one. 02:25.020 --> 02:26.100 Now I wanna, very quickly, 02:26.100 --> 02:27.780 go through the same scenario again, 02:27.780 --> 02:30.150 but we're going to imagine that rather than asking 02:30.150 --> 02:32.250 for a 500 GB hard drive, 02:32.250 --> 02:33.690 maybe this time around you ask 02:33.690 --> 02:36.630 for a 1 TB hard drive instead. 02:36.630 --> 02:38.430 So we're gonna do a second flow 02:38.430 --> 02:39.663 through this diagram. 02:40.830 --> 02:42.630 And imagine that you instead decide 02:42.630 --> 02:45.090 you want the 1 TB drive. 02:45.090 --> 02:45.923 So in this case, 02:45.923 --> 02:47.790 you are, again, walking down the sidewalk. 02:47.790 --> 02:48.930 You see the billboard 02:48.930 --> 02:49.763 and you see that there 02:49.763 --> 02:53.163 is a 1 TB hard drive storage option. 02:54.030 --> 02:55.320 You say, "Oh, that's perfect. 02:55.320 --> 02:58.470 I would love to have a 1 TB hard drive." 02:58.470 --> 03:01.320 So you walk down to the computer store, a second time, 03:01.320 --> 03:02.887 and you say to the salesperson, 03:02.887 --> 03:04.800 "Hey, you know I would love to get one 03:04.800 --> 03:06.600 of those 1 TB hard drives." 03:06.600 --> 03:07.897 And the salesperson says, 03:07.897 --> 03:08.730 "Okay, sure. 03:08.730 --> 03:11.250 Let me just check the store room really quick." 03:11.250 --> 03:13.560 So the salesperson goes back to the store room 03:13.560 --> 03:15.000 and they look at all the hard drives 03:15.000 --> 03:17.310 that they already have in stock. 03:17.310 --> 03:18.720 So these hard drives right here, 03:18.720 --> 03:20.820 inside the store room are essentially hard drives 03:20.820 --> 03:22.800 that have already been created. 03:22.800 --> 03:25.530 They are in existence already. 03:25.530 --> 03:27.690 The salesperson looks through all the stock 03:27.690 --> 03:29.700 that they have and they very quickly realize, 03:29.700 --> 03:34.350 oh no, there is no 1 TB hard drive on stock, on hand, 03:34.350 --> 03:36.150 ready to be sold. 03:36.150 --> 03:39.360 But the salesperson is not going to give up very easily. 03:39.360 --> 03:41.220 The salesperson says, "You know what? 03:41.220 --> 03:43.980 I'm gonna make sure you get what you asked for, 03:43.980 --> 03:47.040 because we were advertising that as an option." 03:47.040 --> 03:49.110 So the salesperson picks up the phone 03:49.110 --> 03:53.130 and very quickly makes a call out to the hard drive factory. 03:53.130 --> 03:54.510 They call a factory and they say, " 03:54.510 --> 03:56.010 Hey, look I got someone right here, 03:56.010 --> 03:57.690 they want a 1 TB hard drive. 03:57.690 --> 03:59.910 I need you to create this thing right now 03:59.910 --> 04:01.800 and ship it on over." 04:01.800 --> 04:04.830 And so the factory puts that hard drive together, 04:04.830 --> 04:07.263 lickety-split, just as fast as you blink, 04:08.460 --> 04:11.250 and they ship it on over to the computer store. 04:11.250 --> 04:14.190 And so now the salesperson has your 1 TB hard drive 04:14.190 --> 04:17.490 that was fabricated, on the fly, just for you. 04:17.490 --> 04:18.990 And they hand the hard drive over, 04:18.990 --> 04:21.090 and you are now a happy little camper 04:21.090 --> 04:23.370 because you have the 1 TB hard drive 04:23.370 --> 04:25.350 that you were asking for. 04:25.350 --> 04:28.470 All right, so that's the entire story, two run throughs. 04:28.470 --> 04:30.450 Now, there's a couple of very quick, 04:30.450 --> 04:32.850 important points that I want to highlight here. 04:32.850 --> 04:36.090 The first important point, is that we had a billboard 04:36.090 --> 04:39.060 that was essentially advertising storage options 04:39.060 --> 04:40.860 that were available. 04:40.860 --> 04:42.390 The second important thing, 04:42.390 --> 04:45.000 is that for those two storage options, 04:45.000 --> 04:48.330 some of them were ready to go and preassembled. 04:48.330 --> 04:51.660 So there were some instances of 500 GB hard drives 04:51.660 --> 04:53.160 that had already been created 04:53.160 --> 04:56.760 and were ready to be handed off to you, the customer. 04:56.760 --> 04:58.350 There were also some storage options 04:58.350 --> 05:00.480 that had been advertised on that billboard 05:00.480 --> 05:01.950 that were not ready to go, 05:01.950 --> 05:04.020 and had to be essentially fabricated 05:04.020 --> 05:09.020 or created, on the fly, to meet your demand. 05:09.210 --> 05:12.540 So, whether it was a hard drive option that was ready to go, 05:12.540 --> 05:15.000 or one that had to be fabricated on the fly, 05:15.000 --> 05:16.650 no big difference to you, the customer, 05:16.650 --> 05:19.590 either way you got what you were asking for. 05:19.590 --> 05:20.423 All right. 05:20.423 --> 05:22.170 So that's the two big points I want you to understand. 05:22.170 --> 05:24.660 So we're not gonna look at another copy of this diagram 05:24.660 --> 05:28.113 that has some Kubernetes terminology applied to it. 05:30.090 --> 05:31.170 Okay. 05:31.170 --> 05:34.440 So here's the Kubernetes version of this diagram. 05:34.440 --> 05:36.840 So first off, you and the previous diagram 05:36.840 --> 05:38.340 were putting together a computer, 05:38.340 --> 05:41.220 and you had realized that you needed a hard drive. 05:41.220 --> 05:43.620 That's very similar to you and I, as developers, 05:43.620 --> 05:46.170 putting together a pod configuration. 05:46.170 --> 05:47.820 When you and I put together a pod 05:47.820 --> 05:50.640 that we know is going to need a persistent volume, 05:50.640 --> 05:53.280 we have to look at a billboard of sorts, 05:53.280 --> 05:55.170 that's going to advertise a couple 05:55.170 --> 05:57.300 of different storage options. 05:57.300 --> 05:58.650 So these different storage options 05:58.650 --> 06:00.570 that are being advertised are what we refer 06:00.570 --> 06:03.420 to as persistent volume claims. 06:03.420 --> 06:06.570 So a persistent volume claim is an advertisement. 06:06.570 --> 06:08.430 It is not an actual volume. 06:08.430 --> 06:11.160 It can't store anything, it's just an advertisement 06:11.160 --> 06:13.560 that says here are the different options 06:13.560 --> 06:15.750 that you have access to for storage 06:15.750 --> 06:18.720 inside of this particular cluster. 06:18.720 --> 06:20.460 You and I, as developers, are going 06:20.460 --> 06:23.550 to write out inside of some config files, 06:23.550 --> 06:25.470 the different persistent volume claims 06:25.470 --> 06:28.170 that are going to be available inside of our cluster. 06:28.170 --> 06:30.960 So you and I are going to write a config file that says 06:30.960 --> 06:35.010 there should be a 500 GB hard drive option available 06:35.010 --> 06:37.710 to all the different parts inside of our cluster. 06:37.710 --> 06:40.020 And we might also write out a config file 06:40.020 --> 06:42.450 that says there is a 1 TB option 06:42.450 --> 06:44.100 that is available as well. 06:44.100 --> 06:46.110 So again, a persistent volume claim 06:46.110 --> 06:47.760 is like an advertisement. 06:47.760 --> 06:50.460 It's saying here is something that you can purchase, 06:50.460 --> 06:51.780 here is something you can get 06:51.780 --> 06:53.823 for your pod when it is created. 06:55.410 --> 06:58.830 Now, when you chose one of those persistent volumes, 06:58.830 --> 07:01.680 you went off to Kubernetes with your pod config, 07:01.680 --> 07:03.270 and you said to Kubernetes, 07:03.270 --> 07:05.347 which was the salesperson, in reality, 07:05.347 --> 07:08.940 "Hey, I just saw that 500 GB hard drive option." 07:08.940 --> 07:09.937 And you said to Kubernetes, 07:09.937 --> 07:13.890 "Hey, I want that 500 GB option, give me one of those." 07:13.890 --> 07:18.890 And so Kubernetes had to go back into some imaginary store, 07:19.020 --> 07:21.870 and it had to look through some number of options 07:21.870 --> 07:24.810 of persistent volumes or storage options, 07:24.810 --> 07:28.710 instances of storage options that were readily available. 07:28.710 --> 07:30.480 And so inside of a Kubernetes cluster, 07:30.480 --> 07:33.090 we might have some number of persistent volumes 07:33.090 --> 07:35.340 that have been created ahead of time. 07:35.340 --> 07:38.310 These are actual instances of hard drives, essentially, 07:38.310 --> 07:41.340 that can be used right away for storage. 07:41.340 --> 07:44.280 Any persistent volume that is created ahead of time, 07:44.280 --> 07:46.290 inside of your cluster, is something that we refer 07:46.290 --> 07:48.570 to as statically provisioned. 07:48.570 --> 07:50.550 So a statically provisioned persistent volume, 07:50.550 --> 07:52.770 is something that we have, very specifically, 07:52.770 --> 07:54.183 created ahead of time. 07:55.740 --> 07:56.573 On the other hand, 07:56.573 --> 08:00.120 we also had a another option that could have been created 08:00.120 --> 08:01.500 on the fly. 08:01.500 --> 08:02.700 So this is where referred to you 08:02.700 --> 08:06.240 as a dynamically provisioned, persistent volume. 08:06.240 --> 08:07.800 It is another storage option 08:07.800 --> 08:09.630 that is not created ahead of time, 08:09.630 --> 08:12.930 it's only created when you putting together your pod, 08:12.930 --> 08:14.010 ask for it. 08:14.010 --> 08:16.650 So you can totally ask for this 1 TB hard drive. 08:16.650 --> 08:17.737 You know you can say it to Kubernetes, 08:17.737 --> 08:19.770 "Give me that 1 TB option, 08:19.770 --> 08:21.780 but that 1 TB hard drive was not going 08:21.780 --> 08:25.290 to be created until you went ahead and asked for it." 08:25.290 --> 08:27.900 So that's the difference between a dynamically provisioned 08:27.900 --> 08:30.510 and a statically provisioned, persistent volume. 08:30.510 --> 08:32.010 Is it created ahead of time, 08:32.010 --> 08:36.000 or is it created just when you immediately ask for it? 08:36.000 --> 08:36.990 All right, so that's it. 08:36.990 --> 08:39.150 That's the big difference between a persistent volume 08:39.150 --> 08:42.300 and a persistent volume claim. 08:42.300 --> 08:45.900 The persistent volume claim is a advertisement of options. 08:45.900 --> 08:47.880 You can ask for one of those options 08:47.880 --> 08:49.200 inside of your pod config. 08:49.200 --> 08:50.730 And when you do, 08:50.730 --> 08:53.760 Kubernetes is going to look at its existing stores 08:53.760 --> 08:54.960 of persistent volume, 08:54.960 --> 08:56.940 and it's either going to give you a volume 08:56.940 --> 08:58.470 that's been created ahead of time, 08:58.470 --> 09:00.970 or it's going to attempt to create one on the fly. 09:02.670 --> 09:04.170 So there's the entire example. 09:04.170 --> 09:05.640 Let's take a quick pause right here. 09:05.640 --> 09:06.960 When we come back to the next section, 09:06.960 --> 09:09.600 we're going to start to update our config files 09:09.600 --> 09:12.180 to create a new persistent volume claim 09:12.180 --> 09:14.370 that's going to create a storage option 09:14.370 --> 09:18.150 that can be claimed, essentially, by our Postgres pod 09:18.150 --> 09:19.440 that we had already created. 09:19.440 --> 09:21.940 So quick break, and I'll see you in just a minute.