WEBVTT 1 00:00.000 --> 00:05.230 So friends, previously we just discussed the concept of loops within Ansible 2 00:05.230 --> 00:05.840 and we learned 3 00:05.840 --> 00:10.140 that this was a core component of programming. What I now want to do is to talk 4 00:10.140 --> 00:10.560 to you about 5 00:10.560 --> 00:14.360 yet another very important subject related to programming and that is 6 00:14.360 --> 00:15.680 conditional statements. 7 00:15.680 --> 00:20.720 So with that said, let's just dive in. So we are really digging deep into the 8 00:20.720 --> 00:21.440 components of 9 00:21.440 --> 00:25.280 programming right now. The good news is, is it with respect to conditionals 10 00:25.280 --> 00:27.040 much like with loops. 11 00:27.040 --> 00:31.040 Whilst we are ultimately using the Python programming language under the hood WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 11 00:27.040 --> 00:31.040 Whilst we are ultimately using the Python programming language under the hood 12 00:31.040 --> 00:32.080 via Ansible, 13 00:32.080 --> 00:36.560 the way this particular concept is exposed to us as an end user of Ansible is 14 00:36.560 --> 00:37.200 once again 15 00:37.200 --> 00:42.240 through a greatly simplified abstraction layer. Nevertheless, it is a good idea 16 00:42.240 --> 00:43.040 to understand 17 00:43.040 --> 00:46.880 what exactly is going on under the hood so that we can correctly apply it 18 00:46.880 --> 00:48.480 within our playbooks. 19 00:48.480 --> 00:52.560 So let's talk about what a conditional statement actually is and why we would 20 00:52.560 --> 00:53.360 want to use it. 21 00:53.360 --> 00:56.790 Now the first thing to say is that this is a very, very important subject. So 22 00:56.790 --> 00:57.600 we definitely 23 00:57.600 --> 01:01.600 want to be paying attention because if you don't pay attention, then you're not WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 23 00:57.600 --> 01:01.600 want to be paying attention because if you don't pay attention, then you're not 24 01:01.600 --> 01:02.080 going to be able to 25 01:02.080 --> 01:06.480 use them with 10 your playbooks. Okay, so confession. What I actually did there 26 01:06.480 --> 01:08.000 was give you an example 27 01:08.000 --> 01:12.800 of a conditional statement. Now in the world of Python programming, the way we 28 01:12.800 --> 01:14.000 define a conditional 29 01:14.000 --> 01:18.220 statement is using the keyword if basically what we're actually asking is a 30 01:18.220 --> 01:19.120 billion question. 31 01:19.120 --> 01:23.030 Now recall we talked about billions that is if something is either true or 32 01:23.030 --> 01:24.960 something is false. 33 01:24.960 --> 01:28.940 It is one or the other. It's a light switch, not a dimmer. So let me give you a 34 01:28.940 --> 01:30.320 very simple example. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 34 01:28.940 --> 01:30.320 very simple example. 35 01:30.320 --> 01:36.720 If you walk into Starbucks and you pay for a coffee, then something is going to 36 01:36.720 --> 01:37.200 happen. 37 01:37.200 --> 01:41.280 And in this case here, what's going to happen is you're going to get a coffee. 38 01:41.280 --> 01:42.720 So this part here, 39 01:42.720 --> 01:46.640 this is actually the condition that we had to meet. And this is the part we're 40 01:46.640 --> 01:47.760 evaluating on a 41 01:47.760 --> 01:52.160 billing condition. Is this true or is this false? And if what we evaluate 42 01:52.160 --> 01:54.320 becomes true, we specify 43 01:54.320 --> 01:58.970 what is going to happen as a consequence. So ask yourself this, if you pay for 44 01:58.970 --> 01:59.840 a coffee, and this 45 01:59.840 --> 02:04.330 is true, I you really did pay for a coffee, then this happens as a consequence, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 45 01:59.840 --> 02:04.330 is true, I you really did pay for a coffee, then this happens as a consequence, 46 02:04.330 --> 02:05.440 you actually get a 47 02:05.440 --> 02:10.410 coffee. Now conversely, if I evaluate this, and it comes to false, so basically 48 02:10.410 --> 02:11.280 I say, if you pay 49 02:11.280 --> 02:16.230 for a coffee, and this is false, I you did not pay for a coffee, the condition 50 02:16.230 --> 02:17.280 below is actually 51 02:17.280 --> 02:21.080 not going to happen, you're not going to get a coffee. Now this might seem 52 02:21.080 --> 02:22.080 almost a trivial 53 02:22.080 --> 02:25.600 example, but this is really how programming logic actually works. It basically 54 02:25.600 --> 02:26.240 breaks down 55 02:26.240 --> 02:30.390 into a series of if statements or conditional statements. Now as we're going to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 55 02:26.240 --> 02:30.390 into a series of if statements or conditional statements. Now as we're going to 56 02:30.390 --> 02:30.800 learn my 57 02:30.800 --> 02:34.160 perspective answer will be actually structure this a little bit differently. 58 02:34.160 --> 02:35.440 What I'm doing here 59 02:35.440 --> 02:39.680 is actually representing the underlying Python. So we don't have to worry about 60 02:39.680 --> 02:40.320 these particular 61 02:40.320 --> 02:44.410 keywords, but they are actually informative to really understand what we're 62 02:44.410 --> 02:45.600 trying to do here. 63 02:45.600 --> 02:49.200 So let's take another example. So let's say we happen to have multiple 64 02:49.200 --> 02:50.880 conditions, we can therefore 65 02:50.880 --> 02:55.990 ultimately specify multiple outcomes or multiple consequences. So let's use the 66 02:55.990 --> 02:56.880 example of the 67 02:56.880 --> 03:01.820 United States and the US, you have to be 21 years of age or older to buy WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 67 02:56.880 --> 03:01.820 United States and the US, you have to be 21 years of age or older to buy 68 03:01.820 --> 03:03.600 alcohol. Whereas if you 69 03:03.600 --> 03:09.340 happen to be 18, you can vote, but you can't buy alcohol. And if you happen to 70 03:09.340 --> 03:10.800 be less than 18, 71 03:10.800 --> 03:14.560 you can't vote or you can't buy alcohol. So really the way we would map this 72 03:14.560 --> 03:15.920 would be the question 73 03:15.920 --> 03:23.240 if you happen to be 21 or over, then as a consequence, you can buy beer and you 74 03:23.240 --> 03:25.120 can vote. But let's say 75 03:25.120 --> 03:28.890 you don't meet that condition, we can have another one to cover it. And by the 76 03:28.890 --> 03:30.000 way, just to be clear WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 77 03:30.000 --> 03:33.920 here, this is not a valid Python code, as you may suggest. This is just an 78 03:33.920 --> 03:35.200 example of pseudocode 79 03:35.200 --> 03:40.750 to help you understand the concept. So let's say you are 18 or over, then you 80 03:40.750 --> 03:41.920 cannot buy beer, 81 03:41.920 --> 03:46.610 but you can vote. And if you happen to be less than 18, then we have another 82 03:46.610 --> 03:48.000 condition, which is 83 03:48.000 --> 03:53.040 no beer or voting. At its core, this is exactly what we're talking about. So if 84 03:53.040 --> 03:54.080 you had a program 85 03:54.080 --> 03:59.600 that tested this logic and someone come up who was 25 years old, if they are 21 86 03:59.600 --> 04:00.640 or above, that is WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 86 03:59.600 --> 04:00.640 or above, that is 87 04:00.640 --> 04:04.740 the condition we're testing, or that would actually be true, 25 is greater than 88 04:04.740 --> 04:06.560 21. Then as a result, 89 04:06.560 --> 04:10.320 they would be allowed to buy beer and they could also vote. Whereas conversely, 90 04:10.320 --> 04:11.200 if someone who was 91 04:11.200 --> 04:15.570 19 years old came up and used a program, this part here would actually evaluate 92 04:15.570 --> 04:16.080 to false, 93 04:16.080 --> 04:20.690 because they're not 21 or over there for this part here would not be applicable 94 04:20.690 --> 04:21.520 . However, 95 04:21.520 --> 04:25.520 we could then jump to the next condition and ask them, are you 18 or over? Well 96 04:25.520 --> 04:26.720 , in that case, 97 04:26.720 --> 04:31.960 the condition is indeed true. So because of that, the consequence here, then WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 97 04:26.720 --> 04:31.960 the condition is indeed true. So because of that, the consequence here, then 98 04:31.960 --> 04:33.520 you cannot buy beer, 99 04:33.520 --> 04:37.980 but you can vote. And then lastly, if someone came up who happened to be 15 100 04:37.980 --> 04:39.360 years old, we could test 101 04:39.360 --> 04:43.370 the condition here. If they are over 21, that would be false. So this part here 102 04:43.370 --> 04:44.560 would not happen. 103 04:44.560 --> 04:49.040 Are they 18 or over? Well, this is also false. So once again, this part here 104 04:49.040 --> 04:50.320 would also not happen. 105 04:50.320 --> 04:53.280 And then they go to the very last condition, if they're under 18, well, that 106 04:53.280 --> 04:54.400 happened to be true. 107 04:54.400 --> 04:59.120 So then we specify what is going to happen, no beer or voting for you. So those 108 04:59.120 --> 05:00.000 are some examples WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 109 05:00.000 --> 05:03.820 of conditional logic in the real world. But as you're going to learn, this can 110 05:03.820 --> 05:04.480 be very, very 111 05:04.480 --> 05:08.540 instructive and useful when dealing with automation. Take for example, we 112 05:08.540 --> 05:10.080 happen to have this device 113 05:10.080 --> 05:13.910 here, which happens to be a red heart machine. And similarly here, we have a 114 05:13.910 --> 05:14.960 device which happened 115 05:14.960 --> 05:19.250 to be a Debian based machine. Let's maybe say it's Ubuntu. If we are managing 116 05:19.250 --> 05:19.760 both of these 117 05:19.760 --> 05:24.440 devices via Ansible, well, the way we actually interact with each device is 118 05:24.440 --> 05:25.200 going to be a little 119 05:25.200 --> 05:29.170 bit different depending on the operating system. Say for example, you want to 120 05:29.170 --> 05:30.240 perform an update of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 120 05:29.170 --> 05:30.240 perform an update of 121 05:30.240 --> 05:34.150 the system, but on a red heart based machine, the package management utility is 122 05:34.150 --> 05:35.680 going to be DNF. 123 05:35.680 --> 05:41.720 So basically, if you are a red heart based machine, then you should use DNF. 124 05:41.720 --> 05:42.560 However, 125 05:42.560 --> 05:47.220 if you happen to be a Debian based machine, then you should use the apt package 126 05:47.220 --> 05:47.840 manager. 127 05:47.840 --> 05:52.000 This is an example of using conditional logic to manage the differences across 128 05:52.000 --> 05:52.720 devices within 129 05:52.720 --> 05:56.410 our inventory, because say for example, if I happen to be on a red heart based 130 05:56.410 --> 05:57.040 machine, 131 05:57.040 --> 06:01.520 which as we can see here, we are on Red Hat Enterprise Linux. If I try to use WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 131 05:57.040 --> 06:01.520 which as we can see here, we are on Red Hat Enterprise Linux. If I try to use 132 06:01.520 --> 06:02.240 the Debian 133 06:02.240 --> 06:06.640 package manager in Sudo, apt updates and to answer, we can see here the command 134 06:06.640 --> 06:07.440 is not found. So if 135 06:07.440 --> 06:10.880 we happen to push out this command automatically to all devices that are 136 06:10.880 --> 06:12.240 inventory, the ones that 137 06:12.240 --> 06:16.620 do not happen to be Debian based are not going to operate. The devices such as 138 06:16.620 --> 06:17.280 this one here, 139 06:17.280 --> 06:22.640 the rail device, for those devices, we would have to use Sudo DNF update. And 140 06:22.640 --> 06:23.680 if we hit enter, 141 06:23.680 --> 06:27.410 suddenly we can update our package manager. And it's going to be using this 142 06:27.410 --> 06:28.320 conditional logic 143 06:28.320 --> 06:31.890 that's going to allow us to control this behavior. Now, just like I said, when WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 143 06:28.320 --> 06:31.890 that's going to allow us to control this behavior. Now, just like I said, when 144 06:31.890 --> 06:33.040 we use the F keyword, 145 06:33.040 --> 06:37.230 this is actually a Python construct. When it comes to utilizing Ansible via the 146 06:37.230 --> 06:38.560 abstraction layer, 147 06:38.560 --> 06:42.770 we actually use a different keyword. Let's find out what that is in the very 148 06:42.770 --> 06:43.440 next video.