1
00:00:03,110 --> 00:00:03,680
‫So in this lecture,

2
00:00:03,680 --> 00:00:09,200
‫let's have a quick discussion about what actually happens in the background when we run the docker

3
00:00:09,200 --> 00:00:10,670
‫container run command.

4
00:00:10,970 --> 00:00:15,350
‫There is a misconception sometimes that Docker is really just running containers and that's its

5
00:00:15,350 --> 00:00:16,240
‫main job.

6
00:00:16,490 --> 00:00:21,740
‫But there's actually so much that's happening in the background that it does in addition to those containers

7
00:00:22,130 --> 00:00:23,650
‫executing commands.

8
00:00:23,660 --> 00:00:28,970
‫When we type docker container run, in the background it's actually going to look for the image that

9
00:00:28,970 --> 00:00:30,960
‫we specified at the end of that command.

10
00:00:31,010 --> 00:00:36,170
‫You remember when we typed nginx at the very end, that was the name of the image we wanted to run

11
00:00:36,530 --> 00:00:37,780
‫as a new container.

12
00:00:37,820 --> 00:00:43,430
‫So it's going to look for that locally in the image cache. If it doesn't find it there, it's going to hop

13
00:00:43,430 --> 00:00:48,420
‫over to Docker Hub, which is its default remote image repository.

14
00:00:49,360 --> 00:00:53,670
‫By default, it'll look it up there and download it and store it in the image cache.

15
00:00:53,680 --> 00:00:58,790
‫So, if we didn't specify a version -- and we didn't, we just typed in nginx --

16
00:00:58,930 --> 00:01:05,500
‫you can actually type in nginx colon some version -- and we'll get into that in next section -- but without

17
00:01:05,500 --> 00:01:08,170
‫specifying a version, it'll just choose the latest.

18
00:01:08,170 --> 00:01:13,950
‫Then, once it's got that image and ready to go, it's going to start up a new container based on that image.

19
00:01:14,110 --> 00:01:15,630
‫It's not going to make a copy of the image.

20
00:01:15,640 --> 00:01:22,660
‫It's actually going to just start a new layer of changes, right on top of where that image left off, and

21
00:01:22,780 --> 00:01:25,300
‫it's going to customize the networking.

22
00:01:25,300 --> 00:01:32,860
‫It's going to give it a specific virtual IP address that's inside a Docker virtual network. It's

23
00:01:32,860 --> 00:01:37,960
‫actually going to open up the port that we specified. If we didn't specify the Publish command, the

24
00:01:37,960 --> 00:01:41,620
‫--publish, it's not going to open up any ports at all.

25
00:01:41,710 --> 00:01:48,580
‫Since we did the 80:80, that's telling it to take the port 80 on the host and forward all that

26
00:01:48,580 --> 00:01:56,260
‫traffic to the port 80 in the container. Then that container finally will actually start using a

27
00:01:56,260 --> 00:02:01,840
‫command specified in the Dockerfile, which will also talk about the next section.

28
00:02:02,040 --> 00:02:05,920
‫You can actually change a majority of these commands from the command line.

29
00:02:06,060 --> 00:02:07,680
‫These are all really defaults.

30
00:02:07,680 --> 00:02:11,110
‫We can actually specify the version of our image.

31
00:02:11,310 --> 00:02:17,160
‫We can specify different ports or the default command to run when it starts that container.

32
00:02:17,400 --> 00:02:21,940
‫But since we had a very simple command, it just used a lot of defaults coming out of the box.

33
00:02:21,960 --> 00:02:25,400
‫As you can see, definitely a lot going on the background.

34
00:02:25,440 --> 00:02:29,130
‫And later on, we're going to dive into each one of these in separate sections.