1 00:00:01,437 --> 00:00:04,890 So we created our first Dockerfile. 2 00:00:04,890 --> 00:00:08,820 Therefore, we then also built our first custom image 3 00:00:08,820 --> 00:00:13,820 and we ran the first container based on a custom image. 4 00:00:13,820 --> 00:00:15,210 Now, there is way more 5 00:00:15,210 --> 00:00:19,210 which we can and will learn about this Dockerfile 6 00:00:19,210 --> 00:00:21,210 and also about the Docker command 7 00:00:21,210 --> 00:00:24,100 and all the subcommands we can run there. 8 00:00:24,100 --> 00:00:26,960 All the different ways of configuring things. 9 00:00:26,960 --> 00:00:29,143 We are going to explore that. 10 00:00:30,010 --> 00:00:33,940 But before we explore anything related to that, 11 00:00:33,940 --> 00:00:36,850 it is important that we fully understand 12 00:00:36,850 --> 00:00:39,430 how an image and a container work 13 00:00:39,430 --> 00:00:40,780 and how they work together. 14 00:00:41,660 --> 00:00:46,250 And for that, let's say in our Node application code, 15 00:00:46,250 --> 00:00:48,360 we wanna change that code. 16 00:00:48,360 --> 00:00:50,590 We wanna change that code and say 17 00:00:50,590 --> 00:00:55,430 My Course Goal! Here for example. 18 00:00:55,430 --> 00:00:59,640 This is a tiny change made to this HTML code 19 00:00:59,640 --> 00:01:04,453 which now should be reflected in our running application. 20 00:01:06,200 --> 00:01:10,330 So if I rerun this command to restart this container 21 00:01:10,330 --> 00:01:12,980 based on this image, which we built, 22 00:01:12,980 --> 00:01:17,040 the application, the Node application starts again. 23 00:01:17,040 --> 00:01:19,880 And if I now reload localhost 3000 24 00:01:19,880 --> 00:01:22,400 I see this application again. 25 00:01:22,400 --> 00:01:25,340 But we also see one problem. 26 00:01:25,340 --> 00:01:28,893 My little change in code isn't reflected here. 27 00:01:29,810 --> 00:01:32,430 Keep in mind, I added an exclamation mark 28 00:01:32,430 --> 00:01:34,183 after My Course Goal. 29 00:01:35,780 --> 00:01:39,120 Here, we still see My Course Goal like this 30 00:01:39,120 --> 00:01:41,420 without the exclamation mark. 31 00:01:41,420 --> 00:01:44,010 So, why is this change not reflected? 32 00:01:44,010 --> 00:01:48,190 I mean, I even restarted the container in the meantime. 33 00:01:48,190 --> 00:01:50,430 In case you didn't do that by the way, 34 00:01:50,430 --> 00:01:52,310 you learned that with docker PS 35 00:01:52,310 --> 00:01:56,600 you can see running containers, then you can pick the name 36 00:01:56,600 --> 00:02:00,700 and run docker stop to stop it and then restart it. 37 00:02:00,700 --> 00:02:03,740 But again, that restarting didn't do anything here. 38 00:02:03,740 --> 00:02:07,393 I don't see that change in my web application. 39 00:02:08,449 --> 00:02:12,080 Because we have to understand how images work, 40 00:02:12,080 --> 00:02:15,430 keep in mind that this is part of our source code, 41 00:02:15,430 --> 00:02:17,900 our Node application code. 42 00:02:17,900 --> 00:02:20,520 What are we doing with that code? 43 00:02:20,520 --> 00:02:24,250 Well, in the Docker file, we instruct Docker, 44 00:02:24,250 --> 00:02:28,960 to in the end, copy everything inside of this project folder 45 00:02:28,960 --> 00:02:32,920 including the server.js file, which holds my source code 46 00:02:32,920 --> 00:02:36,090 into the container file system to be precise 47 00:02:36,090 --> 00:02:38,610 into the app folder. 48 00:02:38,610 --> 00:02:40,500 Then we run npm install, 49 00:02:40,500 --> 00:02:43,550 tell Docker that it should open up port 80 50 00:02:43,550 --> 00:02:46,923 and start the server when the container is launched. 51 00:02:48,020 --> 00:02:50,710 Now, therefore we do one important thing. 52 00:02:50,710 --> 00:02:54,610 We copy our source code into the image, 53 00:02:54,610 --> 00:02:59,000 and we basically take a snapshot of our source code 54 00:02:59,000 --> 00:03:00,943 at the point of time we copied. 55 00:03:01,870 --> 00:03:04,870 If I thereafter edit my source code, 56 00:03:04,870 --> 00:03:08,800 as I did it here when I added this exclamation mark, 57 00:03:08,800 --> 00:03:12,820 this change is not part of the source code in the image. 58 00:03:12,820 --> 00:03:17,820 We need to rebuild our image to copy our updated source code 59 00:03:18,370 --> 00:03:20,750 into a new image. 60 00:03:20,750 --> 00:03:22,750 And that is really crucial. 61 00:03:22,750 --> 00:03:26,160 Now, if this sounds cumbersome and strange 62 00:03:26,160 --> 00:03:28,380 that we have to rebuild our image 63 00:03:28,380 --> 00:03:30,400 every time we change our code, 64 00:03:30,400 --> 00:03:32,100 I have a good message for you. 65 00:03:32,100 --> 00:03:35,220 We will find a more elegant and faster way 66 00:03:35,220 --> 00:03:37,703 of picking up changes in our code later. 67 00:03:38,750 --> 00:03:41,620 But the core takeaway here is important 68 00:03:41,620 --> 00:03:43,680 and will always be true. 69 00:03:43,680 --> 00:03:47,870 Images are basically locked and finished 70 00:03:47,870 --> 00:03:49,640 once you built them. 71 00:03:49,640 --> 00:03:53,350 Everything in the images is read only then, 72 00:03:53,350 --> 00:03:56,090 and you can't edit it from the outside 73 00:03:56,090 --> 00:03:58,110 by simply updating your code 74 00:03:58,110 --> 00:04:01,780 just because you copied that code in the past. 75 00:04:01,780 --> 00:04:04,010 The image doesn't care about the past. 76 00:04:04,010 --> 00:04:06,250 Once this copy operation is done, 77 00:04:06,250 --> 00:04:09,340 you can change your outside code however you want. 78 00:04:09,340 --> 00:04:10,590 You can even delete it 79 00:04:10,590 --> 00:04:13,350 and the image will not be affected. 80 00:04:13,350 --> 00:04:17,540 You need to rebuild to pick up external changes 81 00:04:17,540 --> 00:04:21,363 and basically copy all the updated code into the image. 82 00:04:22,310 --> 00:04:23,143 So therefore, 83 00:04:23,143 --> 00:04:24,310 what we need to do here 84 00:04:24,310 --> 00:04:27,770 is we need to run docker build dot again 85 00:04:27,770 --> 00:04:29,550 to rebuild this image 86 00:04:29,550 --> 00:04:32,203 and therefore to build a new image in the end. 87 00:04:33,990 --> 00:04:36,110 So, let's wait for this operation to finish. 88 00:04:36,110 --> 00:04:37,880 And once we get this new image, 89 00:04:37,880 --> 00:04:39,720 we also got a new image name, 90 00:04:39,720 --> 00:04:43,420 because it now really is a totally new image. 91 00:04:43,420 --> 00:04:45,520 It's almost the same as the previous one, 92 00:04:45,520 --> 00:04:47,570 but technically it's totally different. 93 00:04:47,570 --> 00:04:49,943 It has totally different code inside of it. 94 00:04:51,920 --> 00:04:54,660 And we can now docker run this new image 95 00:04:54,660 --> 00:04:56,663 by using this new image name. 96 00:04:57,600 --> 00:05:01,840 And if we do this now and we reload localhost 3000, 97 00:05:01,840 --> 00:05:04,510 you now see the exclamation mark is there 98 00:05:04,510 --> 00:05:06,840 and this change has now been picked up. 99 00:05:06,840 --> 00:05:08,920 Because we rebuilt a new image 100 00:05:08,920 --> 00:05:10,733 with our new code inside of it. 101 00:05:13,100 --> 00:05:14,960 And I'm putting so much emphasis on that, 102 00:05:14,960 --> 00:05:18,420 because it is super crucial to understand 103 00:05:18,420 --> 00:05:23,420 that an image is really a closed template in the end. 104 00:05:23,480 --> 00:05:26,920 These instructions are executed to create the image, 105 00:05:26,920 --> 00:05:29,350 and thereafter it's locked, it's finished. 106 00:05:29,350 --> 00:05:31,460 And if you change something which you copied 107 00:05:31,460 --> 00:05:34,983 into your image thereafter, that has no impact. 108 00:05:36,370 --> 00:05:37,820 So with that all, 109 00:05:37,820 --> 00:05:42,690 also stop this newly created Docker container here. 110 00:05:42,690 --> 00:05:45,370 And we can now dive a bit deeper into images 111 00:05:45,370 --> 00:05:47,010 and again, also containers. 112 00:05:47,010 --> 00:05:49,793 Because there is more which we need to explore here.