WEBVTT 00:01.290 --> 00:02.490 -: In this section, we're gonna start 00:02.490 --> 00:04.080 to really get a better idea 00:04.080 --> 00:06.730 of what was really occurring on our terminal 00:07.800 --> 00:10.920 when we executed that Docker build command. 00:10.920 --> 00:12.870 We're going to walk through each of these steps 00:12.870 --> 00:15.030 and not really analyze the structure of each of them 00:15.030 --> 00:17.490 but really analyze the effect that they had 00:17.490 --> 00:19.260 on the image that we were building. 00:19.260 --> 00:22.140 So to get started, I first want to talk a little bit 00:22.140 --> 00:23.190 about the output that we saw 00:23.190 --> 00:26.450 in our terminal when we executed the Docker build command. 00:26.450 --> 00:29.220 So first things first, why do we use Docker build? 00:29.220 --> 00:31.290 Well, this is a new command that we have not used 00:31.290 --> 00:33.690 before tied to the Docker CLI. 00:33.690 --> 00:35.640 Remember what we said a little bit ago? 00:35.640 --> 00:37.050 When we create our Docker file, 00:37.050 --> 00:39.060 we then feed it into the Docker client, 00:39.060 --> 00:41.160 which turns around and gives your file off 00:41.160 --> 00:42.690 to the Docker server 00:42.690 --> 00:44.973 and that's what builds your usable image. 00:46.020 --> 00:47.730 So when we ran Docker build dot, 00:47.730 --> 00:52.260 that was us giving our Docker file off to the Docker CLI. 00:52.260 --> 00:54.960 The build command is what we use to take a Docker file 00:54.960 --> 00:57.210 and generate an image out of it. 00:57.210 --> 00:59.310 The dot right here is specifying 00:59.310 --> 01:01.680 what is called the build context. 01:01.680 --> 01:04.620 The build context is essentially the set of files 01:04.620 --> 01:07.050 and folders that belong to our project. 01:07.050 --> 01:08.310 It's a set of files and folders 01:08.310 --> 01:09.840 that we want to kind of encapsulate 01:09.840 --> 01:11.490 or wrap in this container, 01:11.490 --> 01:13.110 and we'll see some better examples 01:13.110 --> 01:15.570 of exactly what the build context is used for 01:15.570 --> 01:16.770 later on throughout the course, 01:16.770 --> 01:19.770 as our docker builds start to get a little bit more complex. 01:21.000 --> 01:23.280 After running that command, we then very quickly 01:23.280 --> 01:26.070 saw a whole bunch of output start to scroll on by. 01:26.070 --> 01:27.600 The first thing I want you to notice here 01:27.600 --> 01:29.610 is that for every line of configuration 01:29.610 --> 01:31.110 that we put into our Docker file, 01:31.110 --> 01:34.140 we got an additional step added to this flow. 01:34.140 --> 01:36.540 So I see step one of three corresponds 01:36.540 --> 01:38.790 to the first line of our Docker file. 01:38.790 --> 01:42.270 I see step two of three corresponding to the second line 01:42.270 --> 01:44.790 and I bet you can guess the third one down here. 01:44.790 --> 01:46.260 Step three of three corresponded 01:46.260 --> 01:48.213 to the third line of the docker file. 01:49.915 --> 01:52.500 Now, with the very first step where we said from Alpine, 01:52.500 --> 01:54.540 the first thing that occurred was that Docker server 01:54.540 --> 01:57.510 looked at our local build cash and it checked to see 01:57.510 --> 02:01.230 if it has ever downloaded an image called Alpine before. 02:01.230 --> 02:02.940 In our case, it probably hasn't. 02:02.940 --> 02:04.140 So the first thing that occurred 02:04.140 --> 02:06.900 was the Docker server reached out to the Docker hub, 02:06.900 --> 02:08.490 which you'll recall is a repository 02:08.490 --> 02:11.190 of existing Docker images that are free for public use. 02:11.190 --> 02:15.570 And it downloaded that image, the image called Alpine. 02:15.570 --> 02:18.150 So pool complete means, yep, it was successfully downloaded 02:18.150 --> 02:20.790 and well, it really tells you that very clearly right here, 02:20.790 --> 02:23.403 downloaded newer image for Alpine latest. 02:24.360 --> 02:26.160 So that first step right there, kind of boring. 02:26.160 --> 02:28.380 We basically just downloaded an initial 02:28.380 --> 02:30.660 starting image to use as a base. 02:30.660 --> 02:32.520 Things started to get a little bit more interesting 02:32.520 --> 02:34.350 on step number two right here. 02:34.350 --> 02:36.360 So there's a couple of lines of code 02:36.360 --> 02:38.430 or output right here that I want you to really 02:38.430 --> 02:40.680 take a very good look at. 02:40.680 --> 02:42.180 You'll notice the first line right here 02:42.180 --> 02:45.540 says running in and then an ID. 02:45.540 --> 02:46.680 So that's very key right there. 02:46.680 --> 02:49.410 I want you to remember that for just a second. 02:49.410 --> 02:50.970 And then a little bit lower, 02:50.970 --> 02:52.980 you'll notice that it says removing 02:52.980 --> 02:55.470 intermediate container and it printed out 02:55.470 --> 02:59.130 the exact same ID that we saw back up there. 02:59.130 --> 03:00.870 So it looks like this ID right here 03:00.870 --> 03:04.860 is the ID of a container, but what container? 03:04.860 --> 03:06.330 We'll dive into that in just a second 03:06.330 --> 03:10.050 when we look at a diagram to kind of explain this flow. 03:10.050 --> 03:12.630 You'll notice that we also saw some very similar output 03:12.630 --> 03:14.190 down here for step three as well, 03:14.190 --> 03:16.560 where it said running in blah, blah, blah. 03:16.560 --> 03:17.940 And then very shortly after that, 03:17.940 --> 03:19.953 removing intermediate container. 03:21.090 --> 03:22.980 One of the last thing I wanna point out here 03:22.980 --> 03:24.870 is that for step number one up here, 03:24.870 --> 03:26.340 you'll notice that there is no kind 03:26.340 --> 03:29.280 of like intermediate container printout. 03:29.280 --> 03:31.800 So it appears that for every instruction 03:31.800 --> 03:34.920 that we added to the docker file besides the first one, 03:34.920 --> 03:39.750 it appears that some like container of sorts was created. 03:39.750 --> 03:43.170 So that in mind, let's flip over to a diagram 03:43.170 --> 03:45.320 and really walk through what just occurred. 03:46.590 --> 03:47.610 All right. 03:47.610 --> 03:48.840 Now, I know we're going through this stuff 03:48.840 --> 03:50.790 like really intense and in depth, 03:50.790 --> 03:53.130 but honestly, getting a very fundamental 03:53.130 --> 03:55.890 or solid understanding of this docker build process 03:55.890 --> 03:58.380 is really gonna help you understand Docker in general. 03:58.380 --> 04:01.110 That's why we're going through so much detail. 04:01.110 --> 04:02.310 Okay, so in this diagram, 04:02.310 --> 04:04.140 we've got a container on the right hand side. 04:04.140 --> 04:06.030 We've got the alpine image on the bottom left, 04:06.030 --> 04:08.970 and then our series of three commands over here. 04:08.970 --> 04:11.490 So the first thing we did was specify from Alpine. 04:11.490 --> 04:13.260 And as we saw, that basically went out 04:13.260 --> 04:16.260 and downloaded the Alpine image off of Docker hub. 04:16.260 --> 04:19.260 Remember that an image has a file system snapshot 04:19.260 --> 04:20.880 and some startup command. 04:20.880 --> 04:22.350 And at this point, we don't really know 04:22.350 --> 04:23.970 what the startup command for Alpine is, 04:23.970 --> 04:25.833 but we don't really care that much. 04:27.090 --> 04:31.020 The next line was the run APK add update ReDIS. 04:31.020 --> 04:34.680 So here's exactly what happened behind the scenes. 04:34.680 --> 04:36.630 When Docker server saw this line 04:36.630 --> 04:39.240 of configuration right here, it looked back 04:39.240 --> 04:41.640 at the last step that just occurred. 04:41.640 --> 04:45.540 So look back at this step from Alpine step. 04:45.540 --> 04:49.620 It looked at the image that came out of that previous step. 04:49.620 --> 04:51.360 The image that came out of the previous step 04:51.360 --> 04:53.193 was the Alpine image. 04:54.060 --> 04:55.530 Then on the run line right here, 04:55.530 --> 04:59.490 it took that image and created a new container out of it. 04:59.490 --> 05:03.720 So in memory, we very temporarily got a brand new container 05:03.720 --> 05:06.810 created at the very start of step number two. 05:06.810 --> 05:08.070 And that's what this running 05:08.070 --> 05:10.050 in blah, blah, blah right here means. 05:10.050 --> 05:12.750 It means that it created a temporary container 05:12.750 --> 05:16.110 out of the image that was sourced during the previous step. 05:16.110 --> 05:19.110 So we can kind of imagine that we took the entire 05:19.110 --> 05:22.080 file system snapshot from the Alpine image 05:22.080 --> 05:25.380 and we stuffed it into this very temporary container 05:25.380 --> 05:28.320 that was created just for the second step right here, 05:28.320 --> 05:30.480 or the second instruction. 05:30.480 --> 05:33.000 After creating this temporary container, 05:33.000 --> 05:34.680 this command right here, 05:34.680 --> 05:38.940 the command that we just added on was executed 05:38.940 --> 05:43.650 inside that container as its primary running process. 05:43.650 --> 05:45.360 So we took that run command, 05:45.360 --> 05:48.030 we took that line or that full command right there, 05:48.030 --> 05:51.780 and we executed it as a process inside of the container. 05:51.780 --> 05:55.170 So this is this container's primary running process. 05:55.170 --> 05:58.860 As we said in the last video, APK is a package manager 05:58.860 --> 06:01.470 that is built into the Alpine image. 06:01.470 --> 06:04.200 So this command executed inside the container, 06:04.200 --> 06:05.550 and while it executed, 06:05.550 --> 06:08.550 it went through the process of downloading ReDIS. 06:08.550 --> 06:09.930 That's what happened right here. 06:09.930 --> 06:11.610 It downloaded and installed ReDIS 06:11.610 --> 06:14.100 and a couple of dependencies for ReDIS. 06:14.100 --> 06:17.160 So we can imagine that during that installation process, 06:17.160 --> 06:19.530 we maybe got some like new folder 06:19.530 --> 06:23.250 on this container's hard drive right there. 06:23.250 --> 06:25.950 Maybe it was something called like Simply ReDIS. 06:25.950 --> 06:28.710 Now, I want this to represent the ReDIS program. 06:28.710 --> 06:30.690 It didn't install it in the route directory 06:30.690 --> 06:32.280 or anything like that, but let's just imagine 06:32.280 --> 06:35.370 that APK add downloaded and installed ReDIS 06:35.370 --> 06:38.490 onto this container's little hard drive right here. 06:38.490 --> 06:43.470 So we now have a container that has a file system snapshot 06:43.470 --> 06:47.670 that contains the newly installed copy of ReDIS. 06:47.670 --> 06:50.220 Now, look at what happened immediately after that. 06:50.220 --> 06:51.690 After that container, or excuse me, 06:51.690 --> 06:53.880 after that package was installed, 06:53.880 --> 06:56.490 we then stopped that container. 06:56.490 --> 07:00.570 We took a file system snapshot of that container 07:00.570 --> 07:02.673 and then we stopped it entirely. 07:03.990 --> 07:05.850 So we're saying right here that temporary container 07:05.850 --> 07:07.500 that was just created, we stop it, 07:07.500 --> 07:11.310 and we then take its current file system snapshot, 07:11.310 --> 07:15.660 and we save it as a temporary image with this ID right here. 07:15.660 --> 07:18.660 So the output of everything inside of step number two 07:18.660 --> 07:22.140 is a new image that contains just the changes 07:22.140 --> 07:23.970 that we made during this step. 07:23.970 --> 07:26.460 So we can now kind of imagine that this ID right here, 07:26.460 --> 07:29.640 this is the ID to a very temporary image. 07:29.640 --> 07:31.560 So I'm now gonna update the image down here 07:31.560 --> 07:33.390 on the top left hand side, 07:33.390 --> 07:37.080 and I'm gonna say that is the 38EC image. 07:37.080 --> 07:42.080 And inside that image, it now has a installed copy of ReDIS. 07:45.270 --> 07:48.750 And we also threw away that intermediate container. 07:48.750 --> 07:51.510 So that is the end result of step number two. 07:51.510 --> 07:54.150 In total, we created a temporary container 07:54.150 --> 07:55.950 out of the Alpine image. 07:55.950 --> 07:59.160 We executed this command inside that container, 07:59.160 --> 08:02.040 and then we took that container's file system 08:02.040 --> 08:04.620 and saved it as a temporary image. 08:04.620 --> 08:07.170 So we now have this very temporary file system 08:07.170 --> 08:09.573 snapshot right here that has ReDIS included. 08:10.800 --> 08:12.720 Then we move onto step number three, 08:12.720 --> 08:15.030 where we execute CMD right here. 08:15.030 --> 08:17.760 So I bet you can imagine what happens here. 08:17.760 --> 08:20.310 With CMD, we're going to look at the image 08:20.310 --> 08:22.950 that was generated during the previous step. 08:22.950 --> 08:24.960 So in this case, the image that was taken 08:24.960 --> 08:28.530 from the previous step is this 38EC image. 08:28.530 --> 08:31.803 We create a new very temporary container out of it, 08:32.640 --> 08:34.140 and when we make that container, 08:34.140 --> 08:36.480 we take the image's file system snapshot 08:36.480 --> 08:38.400 and stuff it into this container. 08:38.400 --> 08:41.910 And then with the CMD, this is setting the primary command 08:41.910 --> 08:44.280 or the primary process of the container. 08:44.280 --> 08:47.340 So the container does not actually execute ReDIS server. 08:47.340 --> 08:49.020 It doesn't execute this command. 08:49.020 --> 08:50.347 It just tells the container, 08:50.347 --> 08:51.810 "Hey, like just so you know, 08:51.810 --> 08:53.850 if you were to ever run for real, 08:53.850 --> 08:57.357 you should be running ReDIS server as your primary command." 08:58.770 --> 09:00.870 So the container is told this is supposed to be 09:00.870 --> 09:02.250 your intermediate or something. 09:02.250 --> 09:04.200 This is supposed to be your primary command. 09:04.200 --> 09:08.280 And then it shuts down that container and takes a snapshot 09:08.280 --> 09:11.940 of its file system and its primary command. 09:11.940 --> 09:14.310 So the end result is successfully built. 09:14.310 --> 09:15.630 This idea right here, 09:15.630 --> 09:18.660 this is the final image that was created 09:18.660 --> 09:20.880 out of this entire series of steps. 09:20.880 --> 09:23.190 So in step number three, at the very end, 09:23.190 --> 09:25.470 we remove the intermediate container, 09:25.470 --> 09:27.780 we take a snapshot of its file system 09:27.780 --> 09:29.310 and its primary command, 09:29.310 --> 09:31.620 and then we save it as an output, 09:31.620 --> 09:35.340 as an image with an ID of FC60. 09:35.340 --> 09:37.950 So here's the container, the very temporary one. 09:37.950 --> 09:40.443 We take a snapshot of its file system, 09:42.060 --> 09:44.220 so I'm gonna put it over here. 09:44.220 --> 09:47.340 And we also take a snapshot of its running primary command, 09:47.340 --> 09:48.990 or excuse me, not running primary command, 09:48.990 --> 09:50.910 but primary command that should be executed 09:50.910 --> 09:53.190 when the container starts up in the future. 09:53.190 --> 09:56.280 And so we specify the startup command as ReDIS server, 09:56.280 --> 09:58.200 and then we save that entire thing 09:58.200 --> 10:02.850 as an image with the ID of FC60. 10:02.850 --> 10:06.330 And so the end result is this right here. 10:06.330 --> 10:09.360 The end result is our image with that ID 10:09.360 --> 10:13.140 that has our full file system snapshot with ReDIS installed, 10:13.140 --> 10:16.470 and a startup command that has been specified. 10:16.470 --> 10:20.040 All right, so at long last, that is the full story. 10:20.040 --> 10:22.230 That is what happened with a Docker file. 10:22.230 --> 10:24.840 Now, the real takeaway that I want you to understand here 10:24.840 --> 10:27.750 is that basically, along every step along the way, 10:27.750 --> 10:29.760 not basically every step, but really every step 10:29.760 --> 10:31.860 along the way with every additional instruction, 10:31.860 --> 10:34.740 we essentially take the image that was generated 10:34.740 --> 10:36.360 during the previous step. 10:36.360 --> 10:38.640 We create a new container out of it, 10:38.640 --> 10:40.650 we execute a command in the container 10:40.650 --> 10:43.680 or make a change to its file system. 10:43.680 --> 10:45.600 We then look at that container, 10:45.600 --> 10:48.360 we take a snapshot of its file system, 10:48.360 --> 10:50.700 and save it as an output for the next 10:50.700 --> 10:52.620 instruction along the chain. 10:52.620 --> 10:55.380 And then when there is no more instructions to execute, 10:55.380 --> 10:58.260 the image that was generated during that last step 10:58.260 --> 11:00.180 is output from the entire process 11:00.180 --> 11:02.523 as the final image that we really care about. 11:03.510 --> 11:05.760 Whew, so that's a lot of information. 11:05.760 --> 11:07.230 So let's take a quick pause right here, 11:07.230 --> 11:09.180 and we'll continue in the next section.