1 00:00:02,270 --> 00:00:04,050 So if we consider this error 2 00:00:04,050 --> 00:00:06,970 that was thrown, what exactly could be the problem 3 00:00:06,970 --> 00:00:10,020 with this newly added bind mount here? 4 00:00:10,020 --> 00:00:13,700 Well, keep in mind that we're binding this folder, 5 00:00:13,700 --> 00:00:17,110 everything in that folder to the app folder. 6 00:00:17,110 --> 00:00:19,600 Now isn't the end kind of means, of course, 7 00:00:19,600 --> 00:00:22,680 that we overwrite the app folder inside 8 00:00:22,680 --> 00:00:25,732 of the container with our local folder, right. 9 00:00:25,732 --> 00:00:30,732 Now we copy everything into that folder, initially here when 10 00:00:31,050 --> 00:00:34,420 the image is created, and we install all dependencies, 11 00:00:34,420 --> 00:00:37,660 but in the end we render all these steps, 12 00:00:37,660 --> 00:00:41,410 which we performed during image creation worthless, 13 00:00:41,410 --> 00:00:44,280 if we then blind this mount to the container, 14 00:00:44,280 --> 00:00:47,640 because we overwrite everything in the app folder anyways 15 00:00:47,640 --> 00:00:49,950 with our local folder. 16 00:00:49,950 --> 00:00:52,650 And this local folder doesn't have 17 00:00:52,650 --> 00:00:54,290 the node modules folder 18 00:00:54,290 --> 00:00:56,600 with all the dependencies this app needs, 19 00:00:56,600 --> 00:00:59,110 and that's the reason for this error we're getting. 20 00:00:59,110 --> 00:01:02,340 The server JS file needs the express package, 21 00:01:02,340 --> 00:01:05,930 the express dependency, and it exists in a container, 22 00:01:05,930 --> 00:01:10,330 because of npm install, it does not exist in my local setup, 23 00:01:10,330 --> 00:01:13,860 because I never ran npm install there. 24 00:01:13,860 --> 00:01:15,990 And since I mount my local folder 25 00:01:15,990 --> 00:01:18,880 to the app folder, we overwrite all 26 00:01:18,880 --> 00:01:21,240 the work we did here when we set up 27 00:01:21,240 --> 00:01:23,450 the image and therefore also the container. 28 00:01:23,450 --> 00:01:26,590 We overwrite this with our local folder, 29 00:01:26,590 --> 00:01:28,530 and that is the problem here. 30 00:01:28,530 --> 00:01:30,940 Now how can we solve this? 31 00:01:30,940 --> 00:01:33,826 Let's first of all understand how containers interact 32 00:01:33,826 --> 00:01:36,400 with volumes and bind mounts. 33 00:01:36,400 --> 00:01:37,628 If we have a container, 34 00:01:37,628 --> 00:01:40,330 and we don't have a volume, and a bind mount, 35 00:01:40,330 --> 00:01:42,330 we can mount both into the container 36 00:01:42,330 --> 00:01:43,860 with the -V flag, 37 00:01:43,860 --> 00:01:46,590 which I showed you a couple of minutes ago. 38 00:01:46,590 --> 00:01:49,730 That means that some folders inside of the container 39 00:01:49,730 --> 00:01:52,150 are mounted, or are connected 40 00:01:52,150 --> 00:01:54,083 to folders on the host machine. 41 00:01:55,280 --> 00:01:59,490 Now let's say we already had files inside of the container. 42 00:01:59,490 --> 00:02:03,708 In that case, they also now exist in the outside volume, 43 00:02:03,708 --> 00:02:06,610 and if you write a new file, it's also added 44 00:02:06,610 --> 00:02:08,789 in the folder on the host machine. 45 00:02:08,789 --> 00:02:10,880 If the container then stands up, 46 00:02:10,880 --> 00:02:14,360 and it finds files in the volume, 47 00:02:14,360 --> 00:02:17,020 and it doesn't have any internal files yet, 48 00:02:17,020 --> 00:02:19,308 it loads the files from the volume. 49 00:02:19,308 --> 00:02:22,570 That's actually what we utilize with the bind mount. 50 00:02:22,570 --> 00:02:25,040 Here we don't have any files inside 51 00:02:25,040 --> 00:02:26,600 of the container, let's say, 52 00:02:26,600 --> 00:02:29,750 but we have files on the local host machine. 53 00:02:29,750 --> 00:02:32,050 In that case, these files 54 00:02:32,050 --> 00:02:34,933 are basically also usable inside of the container, 55 00:02:35,900 --> 00:02:38,690 but now we have kind of both things happening. 56 00:02:38,690 --> 00:02:42,290 We have files inside of the container in the app folder, 57 00:02:42,290 --> 00:02:43,880 because of these instructions, 58 00:02:43,880 --> 00:02:47,160 and we have files and folders outside of the container 59 00:02:47,160 --> 00:02:50,300 in this folder on our local host machine. 60 00:02:50,300 --> 00:02:51,560 And now the good thing is 61 00:02:51,560 --> 00:02:55,690 that Docker does not start overwriting our local files 62 00:02:55,690 --> 00:02:57,410 on our host machine. 63 00:02:57,410 --> 00:02:58,530 This would be pretty bad, 64 00:02:58,530 --> 00:03:00,330 if Docker would be doing that, right. 65 00:03:00,330 --> 00:03:02,440 We could delete a lot of important things 66 00:03:02,440 --> 00:03:04,610 on our computer by accident. 67 00:03:04,610 --> 00:03:06,180 So that's not what's happening. 68 00:03:06,180 --> 00:03:10,083 Docker will not overwrite our local host folder here. 69 00:03:11,080 --> 00:03:13,800 Instead, here, the local host folder, 70 00:03:13,800 --> 00:03:16,490 and the content in it overwrites what's 71 00:03:16,490 --> 00:03:18,290 in the Docker container, 72 00:03:18,290 --> 00:03:19,420 and that's the problem here, 73 00:03:19,420 --> 00:03:22,870 with that we got rid of node modules and so on. 74 00:03:22,870 --> 00:03:26,972 Now to solve this problem, we kind of need to tell Docker, 75 00:03:26,972 --> 00:03:30,150 that there are certain parts 76 00:03:30,150 --> 00:03:34,350 in its internal file system, which should not be overwritten 77 00:03:34,350 --> 00:03:37,370 from outside in case we have such a clash 78 00:03:37,370 --> 00:03:38,950 as we have it here. 79 00:03:38,950 --> 00:03:43,090 And the debt can be achieved with another volume, 80 00:03:43,090 --> 00:03:46,220 which we add to this Docker container 81 00:03:46,220 --> 00:03:48,790 with an anonymous volume actually. 82 00:03:48,790 --> 00:03:51,250 And this will now also show us a use case, 83 00:03:51,250 --> 00:03:54,423 where anonymous volumes can be helpful. 84 00:03:54,423 --> 00:03:57,364 If we add one more volume with -V, 85 00:03:57,364 --> 00:04:02,364 we can find the app/node modules folder. 86 00:04:03,220 --> 00:04:05,200 And it's an anonymous volume, 87 00:04:05,200 --> 00:04:07,000 which we also can add like this, 88 00:04:07,000 --> 00:04:09,850 and not just in the Docker file. 89 00:04:09,850 --> 00:04:12,860 It's an anonymous volume because it has no name, 90 00:04:12,860 --> 00:04:16,329 it would have a name if we add a colon in front of it, 91 00:04:16,329 --> 00:04:18,420 and assign some name here, 92 00:04:18,420 --> 00:04:21,640 but if we don't do that, it's an anonymous volume. 93 00:04:21,640 --> 00:04:23,850 So this is an anonymous volume, 94 00:04:23,850 --> 00:04:26,120 and adding it like this 95 00:04:26,120 --> 00:04:31,120 is equivalent to adding it like this here. 96 00:04:32,670 --> 00:04:35,510 You could do both, but I'll comment this out 97 00:04:35,510 --> 00:04:39,230 with a hash in front of it and go with this approach, 98 00:04:39,230 --> 00:04:42,750 because I then don't have to rebuild the image. 99 00:04:42,750 --> 00:04:45,290 Now why does this help here? 100 00:04:45,290 --> 00:04:49,080 Well, Docker always evaluates all volumes you 101 00:04:49,080 --> 00:04:50,800 are setting on a container, 102 00:04:50,800 --> 00:04:55,800 and if there are clashes, the longer internal path wins. 103 00:04:56,090 --> 00:04:58,120 So for example here we have a clash, 104 00:04:58,120 --> 00:05:02,820 we have app volume which is bound to something, 105 00:05:02,820 --> 00:05:06,400 and we have an app/node modules volume, 106 00:05:06,400 --> 00:05:08,290 which is also bound to something. 107 00:05:08,290 --> 00:05:09,690 We didn't assign a name, 108 00:05:09,690 --> 00:05:12,490 but keep in mind, even for anonymous volumes, 109 00:05:12,490 --> 00:05:14,290 they are managed by Docker, 110 00:05:14,290 --> 00:05:17,670 and there is some mapped folder somewhere 111 00:05:17,670 --> 00:05:19,360 on the local machine. 112 00:05:19,360 --> 00:05:21,780 It's just cleared when a container is removed, 113 00:05:21,780 --> 00:05:24,370 but there is a folder on the host machine, 114 00:05:24,370 --> 00:05:26,303 even for anonymous modules. 115 00:05:26,303 --> 00:05:30,690 So here, Docker sees that we have some volume mapped 116 00:05:30,690 --> 00:05:32,230 to the app folder, 117 00:05:32,230 --> 00:05:36,030 and some volume to the app/node modules folder. 118 00:05:36,030 --> 00:05:39,070 And in that case, the simple rule Docker has 119 00:05:39,070 --> 00:05:43,620 is that the longer the more specific path wins. 120 00:05:43,620 --> 00:05:46,890 So that means we can still bind to the app folder, 121 00:05:46,890 --> 00:05:50,631 but the node modules folder inside of the app folder, 122 00:05:50,631 --> 00:05:54,210 and the node modules folder is the folder created 123 00:05:54,210 --> 00:05:56,640 by the npm install command by the way. 124 00:05:56,640 --> 00:05:59,610 The node modules folder will survive, 125 00:05:59,610 --> 00:06:02,580 it will overwrite the folder that's coming in 126 00:06:02,580 --> 00:06:05,290 from outside because of this module, 127 00:06:05,290 --> 00:06:08,910 and here, we actually pass in no node modules folder, 128 00:06:08,910 --> 00:06:12,091 and therefore this node modules folder overwrites 129 00:06:12,091 --> 00:06:15,120 the non existent node modules folder, 130 00:06:15,120 --> 00:06:16,919 and hence long story short, 131 00:06:16,919 --> 00:06:20,460 the node modules folder, which was created during 132 00:06:20,460 --> 00:06:24,050 the image creation with npm install will survive, 133 00:06:24,050 --> 00:06:27,070 and will actually co exist together 134 00:06:27,070 --> 00:06:30,470 with the bind mount, which still also works. 135 00:06:30,470 --> 00:06:32,620 It's just a node modules folder, 136 00:06:32,620 --> 00:06:34,853 which is kind of excluded you could say. 137 00:06:36,360 --> 00:06:39,531 And therefore now after this long explanation, 138 00:06:39,531 --> 00:06:44,513 if we stop the currently running container, 139 00:06:45,700 --> 00:06:49,993 and we remove this container, 140 00:06:50,930 --> 00:06:53,410 we can run this container now 141 00:06:53,410 --> 00:06:56,150 with this extra anonymous volume added. 142 00:06:56,150 --> 00:07:00,278 If we want to also again with --RM added, 143 00:07:00,278 --> 00:07:02,467 and now this starts, 144 00:07:02,467 --> 00:07:07,280 and now this app also works again, test this works. 145 00:07:07,280 --> 00:07:12,280 Again, we'll see under feedback, awesome.txt, 146 00:07:13,300 --> 00:07:16,587 that file from earlier is also still there, 147 00:07:16,587 --> 00:07:20,040 but now we actually have one additional benefit. 148 00:07:20,040 --> 00:07:23,170 Now if we change something in our HTML file, 149 00:07:23,170 --> 00:07:26,220 for example, I removed that please text again, 150 00:07:26,220 --> 00:07:30,080 and I save that file, if I now reload we see 151 00:07:30,080 --> 00:07:33,030 that change instantly without rebuilding 152 00:07:33,030 --> 00:07:34,430 the image in between, 153 00:07:34,430 --> 00:07:35,680 and the reason for that 154 00:07:35,680 --> 00:07:38,750 is that now we added this bind mount, 155 00:07:38,750 --> 00:07:41,220 which in this case also only works, 156 00:07:41,220 --> 00:07:44,180 if we add this anonymous module to make sure 157 00:07:44,180 --> 00:07:47,360 that node modules folder doesn't get overwritten 158 00:07:47,360 --> 00:07:49,913 by our bind mount folder content.