WEBVTT 00:00.720 --> 00:01.553 -: In the last section, 00:01.553 --> 00:03.990 we found that we were able to connect to Redis CLI 00:03.990 --> 00:06.270 inside of our running Docker container, 00:06.270 --> 00:08.220 and notice how mine is still running over here 00:08.220 --> 00:12.180 on the second window by adding on the -IT flag. 00:12.180 --> 00:13.170 So when I did that, 00:13.170 --> 00:14.940 we saw, yep, we got this prompt here, 00:14.940 --> 00:16.380 we could enter stuff in. 00:16.380 --> 00:19.830 I could then press control C to exit back out. 00:19.830 --> 00:22.031 However, if I tried running this command 00:22.031 --> 00:24.483 without the IT flag, 00:26.160 --> 00:27.510 it appeared that I just got kicked 00:27.510 --> 00:29.610 directly back over to my terminal. 00:29.610 --> 00:31.860 So in this section, I wanna give you a better idea 00:31.860 --> 00:35.670 of what this -IT flag right here is really doing for us. 00:35.670 --> 00:37.020 The first thing you need to understand 00:37.020 --> 00:39.090 is a little bit more about how processes run 00:39.090 --> 00:41.190 inside of a Linux environment. 00:41.190 --> 00:42.240 As a quick reminder, 00:42.240 --> 00:44.490 when you are running Docker on your machine, 00:44.490 --> 00:46.110 every single container that you are running 00:46.110 --> 00:50.730 is running inside of a virtual machine running Linux. 00:50.730 --> 00:53.070 So these processes are really being executed 00:53.070 --> 00:57.030 inside of a Linux world, even if you're on Mac or Windows. 00:57.030 --> 00:59.220 All right, so with that in mind, 00:59.220 --> 01:02.460 in this diagram we've got three different running processes 01:02.460 --> 01:04.680 all inside, in theory, of a running container, 01:04.680 --> 01:07.500 or really inside of a Linux environment. 01:07.500 --> 01:09.810 Every process that we create in a Linux environment 01:09.810 --> 01:12.960 has three communication channels attached to it 01:12.960 --> 01:17.310 that we refer to as stdin, stdout, and stderr. 01:17.310 --> 01:19.500 These channels are used to communicate information 01:19.500 --> 01:23.460 either into the process or out of the process. 01:23.460 --> 01:24.960 Stdin, as you might guess, 01:24.960 --> 01:28.260 is used to communicate information into the process. 01:28.260 --> 01:31.710 So when you are at your terminal and you type stuff in, 01:31.710 --> 01:34.020 the stuff you type is being directed 01:34.020 --> 01:37.530 into a running stdin channel attached to, 01:37.530 --> 01:38.913 say, the Redis CLI. 01:39.900 --> 01:43.290 The stdout channel that is attached to any given process 01:43.290 --> 01:44.760 is going to convey information 01:44.760 --> 01:46.530 that is coming from the process. 01:46.530 --> 01:49.290 So stdout might be redirected 01:49.290 --> 01:50.640 over to your running terminal, 01:50.640 --> 01:52.350 and that's gonna end up as being stuff 01:52.350 --> 01:54.150 that is gonna show up on the screen. 01:55.110 --> 01:56.760 Stderr is very similar, 01:56.760 --> 01:59.370 but it conveys information out of the process 01:59.370 --> 02:01.620 that is kind of like an error in nature. 02:01.620 --> 02:04.470 So if Redis CLI has some error inside of it, 02:04.470 --> 02:06.390 that's gonna be communicated to the outside world 02:06.390 --> 02:08.250 over the stderr channel, 02:08.250 --> 02:10.050 and very similar to stdout, 02:10.050 --> 02:11.370 that's going to be redirected 02:11.370 --> 02:13.470 to show up on the screen of your terminal. 02:15.060 --> 02:17.460 So how's that relate to the IT flag 02:17.460 --> 02:20.670 when we do the Docker exec -IT? 02:20.670 --> 02:21.870 Well, the IT right here 02:21.870 --> 02:24.840 is actually two separate little flags. 02:24.840 --> 02:29.220 In reality, it's a -i and a -t, like so. 02:29.220 --> 02:31.620 But by convention, we usually just kind of shorten it down 02:31.620 --> 02:33.690 to be simply IT, 02:33.690 --> 02:37.380 which is 100% equivalent to the two separate flags. 02:37.380 --> 02:41.220 The -i on here means when we execute this new command 02:41.220 --> 02:42.480 inside the container, 02:42.480 --> 02:45.360 we want to attach our terminal 02:45.360 --> 02:49.170 to the stdin channel of that new running process. 02:49.170 --> 02:51.390 So by adding on the -i flag, 02:51.390 --> 02:52.560 we are saying make sure 02:52.560 --> 02:54.450 that any stuff that I type 02:54.450 --> 02:57.297 gets directed to stdin of Redis CLI. 02:58.440 --> 03:02.130 The -t flag is what kind of makes all this text 03:02.130 --> 03:03.480 show up a little bit pretty. 03:03.480 --> 03:05.790 Now in reality, it's doing a little bit more than that, 03:05.790 --> 03:06.900 but at the end of the day, 03:06.900 --> 03:09.060 the real effect that the -t flag 03:09.060 --> 03:10.800 is to make sure that all the texts 03:10.800 --> 03:13.320 that you are entering in and that is coming out 03:13.320 --> 03:16.020 shows up in a nicely formatted manner on your screen. 03:16.020 --> 03:17.520 And again, it's doing a little bit more 03:17.520 --> 03:18.360 behind the scenes than that, 03:18.360 --> 03:20.880 but at the end of the day, that's kind of its effect. 03:20.880 --> 03:22.530 Let's try attaching 03:22.530 --> 03:25.200 or doing our Docker exec on the running container 03:25.200 --> 03:28.050 one more time and leaving off the -t flag 03:28.050 --> 03:30.300 and just seeing what happens. 03:30.300 --> 03:34.140 So I'll do a Docker PS to get my container's ID again, 03:34.140 --> 03:36.240 then I'll do a Docker exec, 03:36.240 --> 03:39.000 and then we'll do only -i this time, 03:39.000 --> 03:42.750 I'll put the ID in, and then I'll do Redis CLI. 03:42.750 --> 03:43.620 And so now this time, 03:43.620 --> 03:46.080 you'll notice how I have my cursor over here. 03:46.080 --> 03:48.390 It appears that this thing is waiting for input, 03:48.390 --> 03:50.070 but I do not see that kind of 03:50.070 --> 03:52.920 nicely formatted indentation I saw before. 03:52.920 --> 03:56.010 And if I put in like set my value five, 03:56.010 --> 03:58.890 before I had a little bit of auto complete functionality, 03:58.890 --> 04:02.160 but this time that auto complete is definitely not there. 04:02.160 --> 04:03.750 I can still run that command though, 04:03.750 --> 04:05.220 and I still see, okay, 04:05.220 --> 04:07.890 and I can still do get my value, 04:07.890 --> 04:09.120 and I still see the value come out. 04:09.120 --> 04:12.360 But again, all this stuff is not nicely formatted, 04:12.360 --> 04:14.400 and so that's kind of the purpose, 04:14.400 --> 04:16.200 more or less, kind of simplifying things here 04:16.200 --> 04:18.333 just a little bit, of that -t flag. 04:20.070 --> 04:21.090 Okay, so that's pretty much it. 04:21.090 --> 04:22.550 That's the purpose of IT. 04:22.550 --> 04:25.560 It allows us to have stuff that we type into our terminal 04:25.560 --> 04:27.480 directed into that running process 04:27.480 --> 04:29.400 and allows us to get information out 04:29.400 --> 04:31.170 back over to our terminal. 04:31.170 --> 04:32.003 So with that in mind, 04:32.003 --> 04:33.210 let's take a quick break right here 04:33.210 --> 04:34.893 and continue in the next section.