1 00:00:02,130 --> 00:00:05,070 With that, let's leave the world of volumes 2 00:00:05,070 --> 00:00:08,680 and images and copying stuff around and folders and files, 3 00:00:08,680 --> 00:00:11,950 and instead, let's dive into the second, 4 00:00:11,950 --> 00:00:14,710 arguably a bit shorter and easier concept, 5 00:00:14,710 --> 00:00:16,670 I wanna discuss in this module. 6 00:00:16,670 --> 00:00:20,430 And that would be arguments and environment variables, 7 00:00:20,430 --> 00:00:23,240 and that's no typo in the title here. 8 00:00:23,240 --> 00:00:25,810 Instead, I'm talking about two options 9 00:00:25,810 --> 00:00:27,810 you can set in your Dockerfile 10 00:00:27,810 --> 00:00:31,880 and on your docker build and docker run commands 11 00:00:31,880 --> 00:00:35,290 because Docker supports build-time arguments 12 00:00:35,290 --> 00:00:38,390 and runtime environment variables. 13 00:00:38,390 --> 00:00:40,020 Now what do I mean by that? 14 00:00:40,020 --> 00:00:44,590 Arguments allow you to set flexible bits of data, 15 00:00:44,590 --> 00:00:46,110 variables you could say, 16 00:00:46,110 --> 00:00:49,980 in your Dockerfile which you can use in there 17 00:00:49,980 --> 00:00:52,500 to pluck different values 18 00:00:52,500 --> 00:00:54,830 into certain Dockerfile instructions 19 00:00:54,830 --> 00:00:57,650 based on arguments that are provided 20 00:00:57,650 --> 00:01:02,650 with the --build-arg option when you run docker build. 21 00:01:02,980 --> 00:01:06,520 And we'll see this in action in a couple of seconds. 22 00:01:06,520 --> 00:01:08,940 Environment variables on the other hand 23 00:01:08,940 --> 00:01:12,360 are available inside of a Dockerfile like arg, 24 00:01:12,360 --> 00:01:15,730 but args are available in your entire application code 25 00:01:15,730 --> 00:01:17,680 in your running application 26 00:01:17,680 --> 00:01:21,160 and you can set them with the env option 27 00:01:21,160 --> 00:01:23,030 inside of a Dockerfile, 28 00:01:23,030 --> 00:01:25,490 telling Docker that you're expecting 29 00:01:25,490 --> 00:01:28,150 this environment variable to be existent 30 00:01:28,150 --> 00:01:30,590 and then provide concrete values 31 00:01:30,590 --> 00:01:34,200 with the --env option on docker run. 32 00:01:34,200 --> 00:01:37,200 And args and environment variables 33 00:01:37,200 --> 00:01:40,880 allow you to create more flexible images and containers 34 00:01:40,880 --> 00:01:44,170 because you don't have to hard-code everything 35 00:01:44,170 --> 00:01:46,380 into these containers and images. 36 00:01:46,380 --> 00:01:49,900 Instead, you can set it dynamically when you build an image 37 00:01:49,900 --> 00:01:52,570 or even only when you run a container. 38 00:01:52,570 --> 00:01:54,590 Now that might still be a bit abstract, 39 00:01:54,590 --> 00:01:56,053 so let's see it in action. 40 00:01:57,010 --> 00:01:59,520 Now one example I wanna start with here 41 00:01:59,520 --> 00:02:03,390 would be in server JS, the port on which we're listening. 42 00:02:03,390 --> 00:02:04,770 This is port 80, 43 00:02:04,770 --> 00:02:08,169 and that's the default port for HTTP requests, 44 00:02:08,169 --> 00:02:11,360 but during development or for whatever reason, 45 00:02:11,360 --> 00:02:12,950 we might wanna change this, 46 00:02:12,950 --> 00:02:14,150 or we might even have 47 00:02:14,150 --> 00:02:17,660 bigger blocks of code in our application code, 48 00:02:17,660 --> 00:02:20,130 which should run differently 49 00:02:20,130 --> 00:02:24,570 based on input provided from outside, 50 00:02:24,570 --> 00:02:26,630 which still might sound very cryptic. 51 00:02:26,630 --> 00:02:29,710 But let's simply start and it'll make more sense. 52 00:02:29,710 --> 00:02:32,980 Node embraces the concept of environment variables 53 00:02:32,980 --> 00:02:35,950 and you access them in your node code 54 00:02:35,950 --> 00:02:39,730 on a globally available process object. 55 00:02:39,730 --> 00:02:42,740 On that object, you have an env key, 56 00:02:42,740 --> 00:02:45,970 and in there, you can access environment variables 57 00:02:45,970 --> 00:02:48,370 that have been set for the environment 58 00:02:48,370 --> 00:02:51,230 in which this code executes. 59 00:02:51,230 --> 00:02:53,770 And now that's the part you can do with Docker. 60 00:02:53,770 --> 00:02:57,420 You can set such globally available environment variables. 61 00:02:57,420 --> 00:03:00,810 And most programming languages and tools 62 00:03:00,810 --> 00:03:04,770 have some kind of support for such environment variables. 63 00:03:04,770 --> 00:03:06,720 So in this case, for example, 64 00:03:06,720 --> 00:03:10,640 we could expect to get a PORT environment variable, 65 00:03:10,640 --> 00:03:13,310 and typically they're written all uppercase, 66 00:03:13,310 --> 00:03:16,180 which then contains the actual PORT number 67 00:03:16,180 --> 00:03:18,690 that should be used to listen on. 68 00:03:18,690 --> 00:03:20,140 Now if I saved this, 69 00:03:20,140 --> 00:03:22,040 at the moment it wouldn't work though, 70 00:03:22,040 --> 00:03:26,350 because at the moment, this environment variable is not set. 71 00:03:26,350 --> 00:03:29,490 We can set it or announce it 72 00:03:29,490 --> 00:03:31,970 inside of the Dockerfile though. 73 00:03:31,970 --> 00:03:36,130 There we could specify it, maybe here, 74 00:03:36,130 --> 00:03:40,180 by adding the env instruction. 75 00:03:40,180 --> 00:03:41,470 And after env, 76 00:03:41,470 --> 00:03:43,750 you provide the name of the environment variable 77 00:03:43,750 --> 00:03:44,810 which you wanna announce. 78 00:03:44,810 --> 00:03:46,780 In this case, PORT. 79 00:03:46,780 --> 00:03:49,150 As a second argument, 80 00:03:49,150 --> 00:03:52,670 you will set a default value for this environment variable, 81 00:03:52,670 --> 00:03:53,503 for example, 80. 82 00:03:54,760 --> 00:03:58,530 And with that, I ensure that this PORT environment variable 83 00:03:58,530 --> 00:04:02,040 is available in this entire application environment 84 00:04:02,040 --> 00:04:04,693 and that it has a default value of 80. 85 00:04:05,770 --> 00:04:06,603 We can now actually 86 00:04:06,603 --> 00:04:10,870 also use this environment variable here on expose. 87 00:04:10,870 --> 00:04:14,690 Do not hard-code 80 here, but expose PORT. 88 00:04:14,690 --> 00:04:15,810 This is now possible 89 00:04:15,810 --> 00:04:18,870 because it is a registered environment variable here. 90 00:04:18,870 --> 00:04:21,959 However, the syntax is actually not like this. 91 00:04:21,959 --> 00:04:24,640 Instead, you need to add a dollar sign in front of it, 92 00:04:24,640 --> 00:04:27,560 telling Docker that the thing after the dollar sign 93 00:04:27,560 --> 00:04:29,620 is the name of an environment variable. 94 00:04:29,620 --> 00:04:30,453 And with that, 95 00:04:30,453 --> 00:04:32,800 Docker will look for this PORT environment variable 96 00:04:32,800 --> 00:04:35,663 and pluck the value stored in there, in here. 97 00:04:36,870 --> 00:04:38,290 Now with that, 98 00:04:38,290 --> 00:04:42,210 we can first of all rebuild our image. 99 00:04:42,210 --> 00:04:44,737 And I'm going to give it a tag of env. 100 00:04:46,230 --> 00:04:48,330 So build that image. 101 00:04:48,330 --> 00:04:49,870 And thereafter, of course, 102 00:04:49,870 --> 00:04:53,720 also run our container again with the docker run command 103 00:04:53,720 --> 00:04:55,130 to be used all the time, 104 00:04:55,130 --> 00:04:58,933 this time with the env tag here after the image though. 105 00:05:00,520 --> 00:05:03,820 Now I'm still publishing the internal PORT 80 here 106 00:05:03,820 --> 00:05:06,600 because I know that this is the default for this container. 107 00:05:06,600 --> 00:05:08,530 So this should still work. 108 00:05:08,530 --> 00:05:09,723 If I now hit enter, 109 00:05:10,990 --> 00:05:13,870 I'm getting an error that this container is still running, 110 00:05:13,870 --> 00:05:16,130 so let me quickly stop that first. 111 00:05:16,130 --> 00:05:18,670 Then repeat this and hit enter 112 00:05:18,670 --> 00:05:20,363 and everything works as before. 113 00:05:21,280 --> 00:05:23,660 Now the advantage of using environment variables 114 00:05:23,660 --> 00:05:26,080 is that we now can configure this. 115 00:05:26,080 --> 00:05:28,200 When we run this container though, 116 00:05:28,200 --> 00:05:31,130 we're not limited to this hard-coded value. 117 00:05:31,130 --> 00:05:33,270 We just have a default value here, 118 00:05:33,270 --> 00:05:35,390 but we don't have to stick to that. 119 00:05:35,390 --> 00:05:38,620 So again, I can stop this container 120 00:05:38,620 --> 00:05:43,620 and then run this again, but now with an extra option 121 00:05:43,640 --> 00:05:44,900 which I set here. 122 00:05:44,900 --> 00:05:46,500 Let's say here. 123 00:05:46,500 --> 00:05:49,460 You can add the --env option, 124 00:05:49,460 --> 00:05:50,293 and after that, 125 00:05:50,293 --> 00:05:54,110 you can add an environment variable key value pair. 126 00:05:54,110 --> 00:05:56,710 And we can set PORT 127 00:05:56,710 --> 00:06:00,463 equal to 8,000, let's say, like this. 128 00:06:01,760 --> 00:06:04,360 And you can add multiple environment variables here 129 00:06:04,360 --> 00:06:07,203 if you want to, but I'm just setting this. 130 00:06:08,220 --> 00:06:09,490 And of course, this also means 131 00:06:09,490 --> 00:06:12,800 that we now need to expose the internal PORT 8,000 132 00:06:12,800 --> 00:06:15,510 because since we set the environment variable to that, 133 00:06:15,510 --> 00:06:20,510 this 8,000 PORT will be used here and also in the server JS. 134 00:06:21,730 --> 00:06:24,310 But now we don't need to rebuild the image 135 00:06:24,310 --> 00:06:26,070 just to change the PORT. 136 00:06:26,070 --> 00:06:27,840 Thanks to the environment variable, 137 00:06:27,840 --> 00:06:30,770 we can just do it like this in the run command. 138 00:06:30,770 --> 00:06:34,330 And if I start that and reload, it still works, 139 00:06:34,330 --> 00:06:37,863 which means that setting this new PORT was successful. 140 00:06:38,820 --> 00:06:40,200 Now you've got a couple of options 141 00:06:40,200 --> 00:06:42,850 when it comes to setting them on the docker run command. 142 00:06:42,850 --> 00:06:44,620 I showed you --env. 143 00:06:44,620 --> 00:06:47,730 You can also shorten this to just dash E if you want to. 144 00:06:47,730 --> 00:06:49,470 That's also supported. 145 00:06:49,470 --> 00:06:51,780 And if you have multiple environment variables, 146 00:06:51,780 --> 00:06:55,740 you'll simply add multiple dash Es with the key value pairs, 147 00:06:55,740 --> 00:06:57,960 just as we did it for volumes, basically. 148 00:06:57,960 --> 00:07:00,793 There we also had multiple dash V flex. 149 00:07:01,710 --> 00:07:03,840 You can also specify, 150 00:07:03,840 --> 00:07:08,350 if I stop this container, you can also specify a file 151 00:07:08,350 --> 00:07:10,280 that contains your environment variable 152 00:07:10,280 --> 00:07:11,720 if you prefer this. 153 00:07:11,720 --> 00:07:14,670 Often such a file is named .env, 154 00:07:14,670 --> 00:07:16,280 but you don't have to name it like this, 155 00:07:16,280 --> 00:07:17,530 but here I will do that. 156 00:07:17,530 --> 00:07:19,720 And then in this file, you could set up 157 00:07:19,720 --> 00:07:22,320 your environment variable key value pair, 158 00:07:22,320 --> 00:07:24,563 so PORT set to 8,000. 159 00:07:25,450 --> 00:07:28,020 And then you could also run this container 160 00:07:28,020 --> 00:07:31,330 and instead of adding the environment variable here, 161 00:07:31,330 --> 00:07:36,227 you could also just use the --env-file option now, 162 00:07:38,060 --> 00:07:41,030 instead of just --env or -e 163 00:07:41,030 --> 00:07:42,860 and point at that file 164 00:07:42,860 --> 00:07:44,670 that contains your environment variables. 165 00:07:44,670 --> 00:07:46,840 In this case, that's the .env file. 166 00:07:46,840 --> 00:07:49,540 It's in the same folder as I'm currently navigated in 167 00:07:49,540 --> 00:07:50,800 in my terminal here. 168 00:07:50,800 --> 00:07:53,450 And then therefore you should start with dot slash, 169 00:07:53,450 --> 00:07:56,120 which means the .env file in the folder 170 00:07:56,120 --> 00:07:59,330 in which I'm currently in here in my terminal. 171 00:07:59,330 --> 00:08:02,963 And with that, the values will be read in from that file. 172 00:08:04,300 --> 00:08:06,990 And hence this still works if we reload here 173 00:08:06,990 --> 00:08:10,710 because now PORT is still set to 8,000. 174 00:08:10,710 --> 00:08:13,460 The advantage of using such a file could be 175 00:08:13,460 --> 00:08:16,160 that you can always rerun the same command 176 00:08:16,160 --> 00:08:18,930 and just switch your values here in the file, 177 00:08:18,930 --> 00:08:22,920 instead of having to do that in the docker run command. 178 00:08:22,920 --> 00:08:25,050 That's why you might wanna use such a file, 179 00:08:25,050 --> 00:08:27,090 but ultimately it's of course up to you 180 00:08:27,090 --> 00:08:29,280 which approach you prefer. 181 00:08:29,280 --> 00:08:30,220 But it should be clear 182 00:08:30,220 --> 00:08:32,799 why environment variables can be helpful. 183 00:08:32,799 --> 00:08:35,690 They help us run one and the same container 184 00:08:35,690 --> 00:08:39,539 based on one and the same image in different modes, 185 00:08:39,539 --> 00:08:42,000 in different configurations, you could say. 186 00:08:42,000 --> 00:08:45,883 So let me now stop feedback app again, and let's continue.