1 00:00:02,240 --> 00:00:05,860 So that's our application running with Docker now 2 00:00:05,860 --> 00:00:07,220 and it works, right? 3 00:00:07,220 --> 00:00:09,590 Everything is great. 4 00:00:09,590 --> 00:00:12,090 Well, here's what's not so great. 5 00:00:12,090 --> 00:00:15,290 First of all, let's stop this application 6 00:00:15,290 --> 00:00:16,460 which you of course can do. 7 00:00:16,460 --> 00:00:18,550 Let's stop this container. 8 00:00:18,550 --> 00:00:23,210 And since I added dash dash RM when I created the container 9 00:00:23,210 --> 00:00:26,293 it is also automatically removed when it's stopped. 10 00:00:28,230 --> 00:00:30,940 Once it's stopped, let's restart it. 11 00:00:30,940 --> 00:00:33,380 And since I did add dash dash RM 12 00:00:33,380 --> 00:00:37,370 we have to use Docker run again to create a new container 13 00:00:37,370 --> 00:00:41,023 because thanks to RM the previous container was deleted. 14 00:00:42,150 --> 00:00:45,970 Now let's run this container without dash dash RM. 15 00:00:45,970 --> 00:00:50,680 So it's a new container again, with the name feedback app 16 00:00:50,680 --> 00:00:54,350 and therefore, I can of course reload the app and it works. 17 00:00:54,350 --> 00:00:59,150 But you'll notice that if I try to view feedbackawesome.txt, 18 00:00:59,150 --> 00:01:00,890 this file doesn't exist. 19 00:01:00,890 --> 00:01:02,993 It fails to get this file. 20 00:01:03,850 --> 00:01:06,980 And of course, this worked a couple of minutes ago. 21 00:01:06,980 --> 00:01:08,880 Now of course, that's the case 22 00:01:08,880 --> 00:01:11,000 because we deleted the container 23 00:01:11,000 --> 00:01:13,533 when we stopped it the first time. 24 00:01:15,140 --> 00:01:18,790 If I for example, here, readd this, 25 00:01:18,790 --> 00:01:22,820 added again in the newly started container, 26 00:01:22,820 --> 00:01:25,223 we can view it here. 27 00:01:27,140 --> 00:01:31,270 And if I now stop this container, feedback app 28 00:01:31,270 --> 00:01:34,430 and keep in mind that now it will not be removed 29 00:01:34,430 --> 00:01:37,860 because we did not add dash dash RM 30 00:01:37,860 --> 00:01:39,690 on the Docker run command. 31 00:01:39,690 --> 00:01:43,130 So if I now stop it without the container being removed 32 00:01:43,130 --> 00:01:46,020 and I restart it thereafter, 33 00:01:46,020 --> 00:01:47,980 you will notice that now if I reload, 34 00:01:47,980 --> 00:01:50,600 the file is still there. 35 00:01:50,600 --> 00:01:54,620 So the file was not lost because we stopped the container 36 00:01:54,620 --> 00:01:57,280 but because we removed the container. 37 00:01:57,280 --> 00:02:00,370 And I guess that makes a lot of sense. 38 00:02:00,370 --> 00:02:04,330 I talked about this isolation concept in great depth 39 00:02:04,330 --> 00:02:07,800 and I explained depth with the Docker file we build an image 40 00:02:07,800 --> 00:02:11,460 and that image has its own internal file system 41 00:02:11,460 --> 00:02:15,520 which is detached from the hosting machine file system. 42 00:02:15,520 --> 00:02:20,020 And when we then launch Docker container based on the image, 43 00:02:20,020 --> 00:02:24,310 that container is added as a extra thin read-write layer 44 00:02:24,310 --> 00:02:25,890 on top of this image. 45 00:02:25,890 --> 00:02:29,270 So it basically has access to this image file system 46 00:02:29,270 --> 00:02:31,680 and it's able to read and write there 47 00:02:31,680 --> 00:02:33,820 without manipulating the image though. 48 00:02:33,820 --> 00:02:35,710 But it's able to read and write there. 49 00:02:35,710 --> 00:02:38,430 It has its own copy of that you could say 50 00:02:38,430 --> 00:02:41,030 managed in a very efficient way though. 51 00:02:41,030 --> 00:02:44,470 So that makes all sense that we can read and write in there. 52 00:02:44,470 --> 00:02:45,940 But the problem is, 53 00:02:45,940 --> 00:02:48,960 that the file system is inside of the container. 54 00:02:48,960 --> 00:02:52,830 So if we stop it and restart it everything is fine 55 00:02:52,830 --> 00:02:54,770 because the container never changed. 56 00:02:54,770 --> 00:02:57,670 And just because it was stopped does not mean 57 00:02:57,670 --> 00:03:01,050 that its file system is cleared or erased. 58 00:03:01,050 --> 00:03:02,230 If that would be the case 59 00:03:02,230 --> 00:03:05,210 our application code would be gone as well, right? 60 00:03:05,210 --> 00:03:07,460 So that's not happening. 61 00:03:07,460 --> 00:03:10,930 But if we remove a container, then that's different. 62 00:03:10,930 --> 00:03:13,700 Then all the data in the container is cleared 63 00:03:13,700 --> 00:03:17,250 because the container overall is cleared and deleted. 64 00:03:17,250 --> 00:03:20,230 And if we then run a new container, 65 00:03:20,230 --> 00:03:22,510 even if it's spaced on the same image, 66 00:03:22,510 --> 00:03:25,170 all the data that was created and stored 67 00:03:25,170 --> 00:03:27,660 in the previous container is lost, 68 00:03:27,660 --> 00:03:30,800 because the image is read-only. 69 00:03:30,800 --> 00:03:34,620 So the container, when a file is generated in the container 70 00:03:34,620 --> 00:03:37,540 does not write this file into the image. 71 00:03:37,540 --> 00:03:40,620 It writes it in its own read-write layer 72 00:03:40,620 --> 00:03:42,170 which is added on top. 73 00:03:42,170 --> 00:03:44,660 Therefore, if the container is removed 74 00:03:44,660 --> 00:03:48,180 we're just left with the image which was never changed. 75 00:03:48,180 --> 00:03:50,620 So when we then start a new container 76 00:03:50,620 --> 00:03:54,600 well, that starts with the same basic file system again 77 00:03:54,600 --> 00:03:57,500 without the changes made by the previous container 78 00:03:57,500 --> 00:04:00,670 which might've been executed on the same image. 79 00:04:00,670 --> 00:04:04,110 And that's a core idea of Docker, multiple containers 80 00:04:04,110 --> 00:04:07,770 based on the same image are totally isolated 81 00:04:07,770 --> 00:04:08,980 from each other. 82 00:04:08,980 --> 00:04:10,990 But here of course, that's a problem. 83 00:04:10,990 --> 00:04:13,570 It means that we lose this text file 84 00:04:13,570 --> 00:04:18,029 if we stop the container and remove it thereafter. 85 00:04:18,029 --> 00:04:22,019 And in many applications, this behavior is a problem 86 00:04:22,019 --> 00:04:23,550 because here, for example, 87 00:04:23,550 --> 00:04:26,860 we wanna keep those feedback text files around 88 00:04:26,860 --> 00:04:29,100 even if a container is deleted. 89 00:04:29,100 --> 00:04:32,420 We would have a comparable scenario if we would be dealing 90 00:04:32,420 --> 00:04:36,600 with user accounts or with product data submitted by users 91 00:04:36,600 --> 00:04:38,770 or any other kind of data 92 00:04:38,770 --> 00:04:41,690 which shouldn't be disappearing suddenly 93 00:04:41,690 --> 00:04:46,000 but which instead should survive containers being deleted. 94 00:04:46,000 --> 00:04:47,810 Because in reality, you're going 95 00:04:47,810 --> 00:04:49,970 to remove containers quite a bit. 96 00:04:49,970 --> 00:04:52,080 If we change something about our code 97 00:04:52,080 --> 00:04:55,130 and be built a new image and start a new container 98 00:04:55,130 --> 00:04:57,400 will not restart the old container. 99 00:04:57,400 --> 00:04:59,030 We wanna use the new container 100 00:04:59,030 --> 00:05:01,860 which uses the latest code snapshot. 101 00:05:01,860 --> 00:05:05,350 So therefore, in that case, we would be losing all the data. 102 00:05:05,350 --> 00:05:08,010 And that's exactly the problem I've been describing 103 00:05:08,010 --> 00:05:09,750 over the last minutes. 104 00:05:09,750 --> 00:05:12,500 So now that we know the problem really well 105 00:05:12,500 --> 00:05:16,430 and that we know that containers are able to write data 106 00:05:16,430 --> 00:05:20,140 but that this data is lost when the container is removed 107 00:05:20,140 --> 00:05:22,270 now that we know all of that, 108 00:05:22,270 --> 00:05:23,603 what is the solution?