WEBVTT 00:00.750 --> 00:02.730 -: In the last section, we saw that making a change 00:02.730 --> 00:05.340 to our index.js file and then rebuilding 00:05.340 --> 00:09.330 the image caused the copy step to be completely invalidated. 00:09.330 --> 00:12.270 We had to rerun copy and every step after it, 00:12.270 --> 00:13.920 which means we had to sit through 00:13.920 --> 00:16.440 and wait for all of our dependencies to be installed 00:16.440 --> 00:18.480 through run NPM install. 00:18.480 --> 00:20.070 So in this section, we're gonna try to figure out 00:20.070 --> 00:22.560 a way to avoid having to completely 00:22.560 --> 00:24.480 reinstall all dependencies just 00:24.480 --> 00:26.130 because we made a little change to one 00:26.130 --> 00:28.770 of the source code files inside of our project. 00:28.770 --> 00:29.790 So here's what we'll do. 00:29.790 --> 00:32.040 We're gonna take our current build process 00:32.040 --> 00:33.330 inside of the Docker file 00:33.330 --> 00:35.880 and we're gonna split the copper copy operation 00:35.880 --> 00:39.030 out into two different steps. 00:39.030 --> 00:41.550 The only thing that NPM install right here requires 00:41.550 --> 00:45.090 in order to run successfully is the package.js on file. 00:45.090 --> 00:46.110 That's all we care about. 00:46.110 --> 00:48.180 We don't care about the index.js file 00:48.180 --> 00:51.000 or any other file inside of here. 00:51.000 --> 00:53.400 So during this initial copy step, 00:53.400 --> 00:55.350 I'm gonna say the only thing that I want to 00:55.350 --> 00:58.473 copy is the package.js on file. 00:59.910 --> 01:01.800 So I just changed the instruction right here. 01:01.800 --> 01:05.370 It now says, Look in the current working directory, or look 01:05.370 --> 01:09.090 in the directory specified by the build context argument 01:09.090 --> 01:11.140 of Docker run, or excuse me, Docker build 01:12.044 --> 01:15.060 and find the package.js on file and then copy 01:15.060 --> 01:19.470 that into the current working directory of the container. 01:19.470 --> 01:20.880 We'll then rerun, or excuse me, 01:20.880 --> 01:23.160 we will then run NPM install. 01:23.160 --> 01:26.220 And then after we install all those dependencies, 01:26.220 --> 01:28.710 we'll copy over everything else. 01:28.710 --> 01:32.433 And so we'll do a copy dot slash dot slash like so. 01:34.170 --> 01:36.660 So think about what is gonna happen now as you start to work 01:36.660 --> 01:39.900 on your project, you can make as many changes as you want 01:39.900 --> 01:43.860 to the index.js file and it will not invalidate the cache 01:43.860 --> 01:45.840 for either of these steps right here. 01:45.840 --> 01:48.810 The only time that NPM is NPM install is going to 01:48.810 --> 01:50.640 be executed again, is if we make 01:50.640 --> 01:54.630 a change to that step or any step above it. 01:54.630 --> 01:56.790 And so in other words, the really only effect 01:56.790 --> 01:58.620 this is gonna have is if we make a change 01:58.620 --> 02:00.390 to the package.js on file. 02:00.390 --> 02:03.540 That's really the only situation in which NPM install 02:03.540 --> 02:07.920 will normally be executed again during the build process. 02:07.920 --> 02:10.350 All right, so let's try building this again 02:10.350 --> 02:11.670 and then starting the container up 02:11.670 --> 02:14.120 and just making sure that everything still works. 02:15.240 --> 02:16.860 All right, so I'm gonna flip back over. 02:16.860 --> 02:20.610 I'll do a Docker build dash t, Steven Greiter, 02:20.610 --> 02:25.440 again your Docker ID, not mine, Simple web and then we'll 02:25.440 --> 02:28.173 specify the build context with that simple dot. 02:29.010 --> 02:30.270 So I'm gonna rerun this. 02:30.270 --> 02:32.280 Now we have made a change to the Docker files 02:32.280 --> 02:35.100 so we are gonna see some steps rerun, and then 02:35.100 --> 02:38.580 we eventually get our successfully tagged and built image. 02:38.580 --> 02:40.800 Now before trying to run it, I want you to run 02:40.800 --> 02:42.960 the same command a second time. 02:42.960 --> 02:45.273 So same thing, no changes whatsoever. 02:46.380 --> 02:49.020 So that time it went extremely quickly because we were 02:49.020 --> 02:52.050 able to use the cache version of every single step. 02:52.050 --> 02:54.900 So now let's imagine that we are doing some normal changes 02:54.900 --> 02:57.180 to our application and a normal change would 02:57.180 --> 02:59.640 probably be a change the index.js file. 02:59.640 --> 03:01.110 So maybe we decide that we don't 03:01.110 --> 03:03.540 wanna say bye there anymore. 03:03.540 --> 03:07.680 Maybe instead we wanna send back, How are you doing? 03:07.680 --> 03:10.200 So we've now made a change to the index.js file 03:10.200 --> 03:12.660 and we definitely need to rebuild our image 03:12.660 --> 03:14.160 cuz we do not have any support 03:14.160 --> 03:17.190 for kind of hot reloading of the index.js file 03:17.190 --> 03:19.230 or a project file into the container. 03:19.230 --> 03:21.423 So we have to rebuild the image. 03:22.560 --> 03:23.730 So I'll go back over. 03:23.730 --> 03:26.823 I'm going to rerun the same command for a third time. 03:28.560 --> 03:31.170 And we saw that it executed very quickly 03:31.170 --> 03:32.760 because the only change that we made 03:32.760 --> 03:36.060 to any step along the way was step number five. 03:36.060 --> 03:37.860 We copied over the entire content 03:37.860 --> 03:39.960 so that directory Docker detected 03:39.960 --> 03:41.970 that we made a change to one of those files. 03:41.970 --> 03:45.390 And so it reran that step and every step after it. 03:45.390 --> 03:48.330 But we did not have to rerun the NPM install step 03:48.330 --> 03:51.480 and reinstall those modules, which would've taken, 03:51.480 --> 03:53.520 you know in our application not very long, 03:53.520 --> 03:54.660 but in a real application, 03:54.660 --> 03:57.330 it could take several minutes to run. 03:57.330 --> 04:00.810 All right, so the real lesson to learn here is that yes 04:00.810 --> 04:03.600 it does make a difference the order in which you put 04:03.600 --> 04:06.180 down all these instructions into your Docker file 04:06.180 --> 04:09.270 and wherever possible it is kind of nice to segment 04:09.270 --> 04:11.550 out the copy operations to make sure 04:11.550 --> 04:14.160 that you are only copying the bare minimum 04:14.160 --> 04:15.933 for each successive step. 04:16.830 --> 04:19.710 All right, so that's pretty much it for this application. 04:19.710 --> 04:22.680 Now, I hope that it was not terribly annoying 04:22.680 --> 04:25.950 for me to show you kind of like some of the wrong way 04:25.950 --> 04:28.230 of doing things and then correct them along the way. 04:28.230 --> 04:29.910 I hope that it was kind of nice to see 04:29.910 --> 04:33.120 the air messages appear and see the changes that we made. 04:33.120 --> 04:35.340 Of course, we could have put the right Docker file together 04:35.340 --> 04:36.990 from the get go, but I don't know, 04:36.990 --> 04:39.180 you probably may have not learned quite as much 04:39.180 --> 04:40.620 as seeing the errors occur 04:40.620 --> 04:42.783 and then fixing them in as they occurred. 04:43.770 --> 04:45.690 Now I think this application has turned out pretty well 04:45.690 --> 04:49.920 but it's definitely a very, very basic operation. 04:49.920 --> 04:51.420 So let's take a quick break right now. 04:51.420 --> 04:52.620 We're gonna come back the next section 04:52.620 --> 04:53.453 and we'll start working 04:53.453 --> 04:56.760 on a much more advanced Docker project. 04:56.760 --> 04:58.410 So I'll see you in just a minute.