1 00:00:02,180 --> 00:00:04,426 By now we explored the core concepts 2 00:00:04,426 --> 00:00:07,370 about Images and Containers. 3 00:00:07,370 --> 00:00:10,027 And I just want to provide a first summary, 4 00:00:10,027 --> 00:00:14,752 on those concepts to ensure we're all on the same page. 5 00:00:14,752 --> 00:00:18,610 With Docker, it's all about Our Code in the end. 6 00:00:18,610 --> 00:00:19,797 Our application we're building 7 00:00:19,797 --> 00:00:22,952 for example our web application. 8 00:00:22,952 --> 00:00:27,273 We put that code that makes up our application, 9 00:00:27,273 --> 00:00:29,182 into a so called Image. 10 00:00:29,182 --> 00:00:31,386 And we don't just put Our Code in there, 11 00:00:31,386 --> 00:00:33,629 but also the Environment, 12 00:00:33,629 --> 00:00:37,110 the tools we need to execute that Code. 13 00:00:37,110 --> 00:00:40,053 You learned that you can create such an Image, 14 00:00:40,053 --> 00:00:42,625 by creating such a Dockerfile, 15 00:00:42,625 --> 00:00:46,113 where you provide detailed instructions, 16 00:00:46,113 --> 00:00:49,670 on what should go into the Image, 17 00:00:49,670 --> 00:00:52,860 which base image you might be using, 18 00:00:52,860 --> 00:00:55,981 which code and which dependencies should be copied in there, 19 00:00:55,981 --> 00:01:00,871 if maybe some setup step like npm install is required, 20 00:01:00,871 --> 00:01:04,804 and if you then want to open up some internal port, 21 00:01:04,804 --> 00:01:06,712 so that you can listen to that 22 00:01:06,712 --> 00:01:09,456 from outside of the imagined deal 23 00:01:09,456 --> 00:01:12,763 for ultimately outside of the container in the end. 24 00:01:14,195 --> 00:01:16,117 And that's of course important. 25 00:01:16,117 --> 00:01:21,056 Docker ultimately is about containers, not images. 26 00:01:21,056 --> 00:01:24,458 But images are an important building block, 27 00:01:24,458 --> 00:01:29,458 they are the template, the blueprint for your containers. 28 00:01:29,532 --> 00:01:31,868 You can then instantiate, 29 00:01:31,868 --> 00:01:36,868 run multiple containers based on an Image. 30 00:01:36,937 --> 00:01:41,600 The Image is the thing that contains your Code and so on. 31 00:01:41,600 --> 00:01:42,958 The container as you learned 32 00:01:42,958 --> 00:01:46,948 is just an extra thin layer on top of the Image, 33 00:01:46,948 --> 00:01:49,205 but still the container in the end 34 00:01:49,205 --> 00:01:53,729 is your running application, based on an image, 35 00:01:53,729 --> 00:01:55,531 but then once it is running, 36 00:01:55,531 --> 00:01:59,633 standalone and independent from other containers 37 00:01:59,633 --> 00:02:01,160 that might be running. 38 00:02:01,160 --> 00:02:02,862 I want to emphasize though, 39 00:02:02,862 --> 00:02:06,259 that a container does not copy over the code 40 00:02:06,259 --> 00:02:10,774 and the environment from the image into a new container 41 00:02:10,774 --> 00:02:11,943 into a new file. 42 00:02:11,943 --> 00:02:13,783 That is not what's happening. 43 00:02:13,783 --> 00:02:18,430 A container will use the environment stored in an image, 44 00:02:18,430 --> 00:02:22,020 and then just add this extra layer on top of it, 45 00:02:22,020 --> 00:02:25,390 this running node server process for example, 46 00:02:25,390 --> 00:02:29,770 and allocate resources, memory and so on 47 00:02:29,770 --> 00:02:30,839 to run the application, 48 00:02:30,839 --> 00:02:33,627 but it will not copy that code. 49 00:02:33,627 --> 00:02:36,401 So Our Code and the node environment, 50 00:02:36,401 --> 00:02:39,531 is not getting copied three times here. 51 00:02:39,531 --> 00:02:42,015 If we have one image and two containers, 52 00:02:42,015 --> 00:02:46,330 it exists only once in the image and to containers, 53 00:02:46,330 --> 00:02:49,453 then utilize that image and the code in it. 54 00:02:49,453 --> 00:02:51,362 This is how Docker manages this, 55 00:02:51,362 --> 00:02:54,233 and that's of course very efficient. 56 00:02:54,233 --> 00:02:56,745 And that's the core idea behind Docker. 57 00:02:56,745 --> 00:03:00,371 Having those isolated environments that contain your app, 58 00:03:00,371 --> 00:03:03,400 and everything that is required to run that app, 59 00:03:03,400 --> 00:03:07,014 all the environment, all the tools like node js, 60 00:03:07,014 --> 00:03:10,200 and having all of that inside of this isolated container. 61 00:03:10,200 --> 00:03:11,990 That's what Docker is about, 62 00:03:11,990 --> 00:03:14,434 and that will be covered thus far, 63 00:03:14,434 --> 00:03:16,593 over the last lectures.