WEBVTT 00:00.000 --> 00:01.290 -In this lecture, 00:01.290 --> 00:05.860 we will take a look at the Count Meta-Argument and its uses in Terraform. 00:06.670 --> 00:10.010 One of the easiest ways to create multiple instances 00:10.010 --> 00:13.440 of the local file is to make use of the count meta-argument. 00:13.670 --> 00:14.930 To do this, 00:14.930 --> 00:18.810 simply add an argument called count with a value greater than one. 00:19.080 --> 00:22.230 Here, we have used count is equal to three. 00:22.440 --> 00:24.950 When we try to run Terraform plan now, 00:24.950 --> 00:29.140 we can see that Terraform tries to create three resources instead of one. 00:30.680 --> 00:35.970 In the output of the Terraform apply command, we can see that three resources are created. 00:35.970 --> 00:41.870 The resources are identified by pet[0], where zero is within square brackets, 00:41.870 --> 00:44.210 pet[1] and pet[2]. 00:44.780 --> 00:48.580 The resource is now considered to be a list of resources 00:48.580 --> 00:51.530 with elements at index 0, 1 and 2. 00:51.780 --> 00:55.100 However, there is one problem with this approach. 00:55.760 --> 00:58.580 Since we have only specified the count, 00:58.580 --> 01:01.940 Terraform will try to create the same resource three times. 01:01.940 --> 01:04.330 Since the filename is not unique, 01:04.330 --> 01:07.110 Terraform will recreate the same file three times 01:07.110 --> 01:11.250 rather than creating three separate files which defeats the purpose of this task. 01:12.010 --> 01:17.220 A better way to do this and make sure that all the three resources have unique filenames 01:17.220 --> 01:20.120 is to make use of a list variable for filename. 01:20.570 --> 01:21.830 To do this, 01:21.830 --> 01:24.950 we have used default values with three elements, 01:24.950 --> 01:28.400 each corresponding to the name of the file that we want to create. 01:29.070 --> 01:30.080 Next, 01:30.080 --> 01:34.050 we want Terraform to make use of each element of this list as the value 01:34.050 --> 01:35.430 of the filename argument. 01:35.830 --> 01:37.300 In this example, 01:37.300 --> 01:41.450 Terraform should make three iterations as the count has a value of three. 01:41.760 --> 01:47.900 The first iteration should pick up the element at index 0 which is the file called pets.txt. 01:48.170 --> 01:52.700 This is followed by element at index 1 which is dogs.txt 01:52.700 --> 01:56.400 and finally cats.txt at index 2. 01:57.070 --> 02:02.380 To use this within the configuration file, we can make use of count.index 02:02.380 --> 02:05.060 in the expression for filename like this. 02:05.850 --> 02:08.070 Now when we are on Terraform apply, 02:08.070 --> 02:12.220 we can see that there are three files created inside this /root directory. 02:12.850 --> 02:17.140 What if we were to add a few more elements to the list in the future? 02:17.140 --> 02:23.490 Say we wanted to add a few more files by the name of /root/cows.txt 02:23.490 --> 02:25.350 and ducks.txt. 02:25.740 --> 02:28.560 If we were to apply this configuration now, 02:28.560 --> 02:31.800 we would see that it would still create only three files, 02:31.800 --> 02:35.400 because we have set the count to a static value of 3. 02:35.890 --> 02:40.790 We want the count to automatically pick up the number of items that are defined 02:40.790 --> 02:42.200 within the filename variable. 02:42.200 --> 02:43.380 To do this, 02:43.380 --> 02:47.140 we can set set the value of count to use a built-in function 02:47.140 --> 02:48.950 that would return the length of the list. 02:49.310 --> 02:54.290 This built-in function called length will set the value of count to 5. 02:55.040 --> 02:57.810 Terraform offers several built-in functions 02:57.810 --> 03:00.760 that allow us to manipulate values within expressions. 03:00.760 --> 03:04.840 One simple function that we can use here is the length function. 03:05.500 --> 03:09.210 The Length function is used to calculate the size of a list 03:09.210 --> 03:12.530 and we can use this function in the count meta-argument 03:12.530 --> 03:15.590 to dynamically determine the size of the filename variable. 03:16.470 --> 03:19.100 We are now ready to run Terraform apply. 03:19.100 --> 03:20.660 Before we do that, 03:20.660 --> 03:23.750 let’s change the default value for the filename variable 03:23.750 --> 03:25.210 back to three elements. 03:26.230 --> 03:27.420 That is it. 03:27.420 --> 03:30.190 If we run Terraform plan and apply now, 03:30.190 --> 03:34.320 we should see that three resources with distinct files names have been created. 03:35.390 --> 03:40.200 There is however a significant drawback when using the count meta-argument 03:40.200 --> 03:41.900 to loop through variables this way. 03:41.900 --> 03:46.140 To illustrate this, lets see the same example but this time, 03:46.140 --> 03:50.370 let us remove the element /root/pets.txt from the list. 03:51.410 --> 03:53.620 If we run Terraform plan now, 03:53.620 --> 03:57.050 we see that instead of deleting just one resource 03:57.050 --> 04:00.390 with the filename /root/pets.txt, 04:00.390 --> 04:04.300 Terraform is replacing two resources and deleting one resource. 04:04.690 --> 04:06.180 Why does it do that? 04:06.520 --> 04:10.360 We only want to remove the first element in this list 04:10.360 --> 04:14.510 and it looks like all elements are going to be replaced by this operation. 04:15.300 --> 04:19.590 To see why this is happening, let us first understand how count works. 04:19.960 --> 04:25.750 As we saw before, when we use count, the resources become a list of resources. 04:26.160 --> 04:28.120 To see this using Terraform, 04:28.120 --> 04:31.220 let us add an output variable to the main.tf file 04:31.220 --> 04:33.220 to print all details of this resource. 04:33.470 --> 04:35.720 Using the Terraform output command, 04:35.720 --> 04:38.950 we can see that the resource is now in the format of a list. 04:39.740 --> 04:44.480 Originally, the resource called pet is a list with three resources, 04:44.480 --> 04:46.830 each identified by its index. 04:46.830 --> 04:51.880 The first resource in the list creates the file by the name pets.txt 04:51.880 --> 04:55.090 and it is identified by pet with the index [0], 04:55.090 --> 04:58.200 zero enclosed in square brackets since it's a list. 04:58.590 --> 05:04.120 The second resource element is pet[1] which creates a file called dogs.txt 05:04.120 --> 05:09.230 and the third resource is pet[2], which creates a file called cats.txt. 05:09.920 --> 05:12.820 The first element in a list is always zero. 05:12.820 --> 05:18.280 As a result, when we deleted the element called /root/pets.txt, 05:18.280 --> 05:24.620 which was at index 0 to begin with, the element with value /root/dogs.txt 05:24.620 --> 05:27.350 shifts up and takes its place at index 0. 05:27.350 --> 05:33.720 Likewise, /root/cats.txt becomes the element at index 1 and the list 05:33.720 --> 05:35.590 now has only two elements in it. 05:36.460 --> 05:38.870 When we run Terraform plan now, 05:38.870 --> 05:42.990 Terraform can see that that the resources at index pet[0] and pet[1] 05:42.990 --> 05:44.740 have to be destroyed and replaced. 05:44.740 --> 05:47.080 This is owing to the change in their filenames. 05:47.080 --> 05:51.610 There is no resource pet[2], so it will delete this resource entirely. 05:52.240 --> 05:56.300 Although after the apply operation we will have the resources created 05:56.300 --> 05:59.760 as per our intended end state, this is not an ideal approach. 05:59.760 --> 06:03.080 We may not want the resources to be destroyed and recreated 06:03.080 --> 06:06.420 just because we removed an unrelated element from the list. 06:06.420 --> 06:09.150 We will see how to do fix this in the next lecture. 06:09.770 --> 06:13.600 Now, let’s head over to the hands-on labs and practice working 06:13.600 --> 06:15.780 with the count meta-arguments in Terraform.