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Iterating over Lists in Terraform

Lesson Content

Getting Started with Terraform on SAP BTP

SAP_MOOC_terra1_unit5_lesson4_ITERAT_Video.mp4

Hello, welcome to Unit 4 and Lesson 4, where we will be iterating over lists in Terraform. We are now in the last step of our overall journey, where we are executing on the goals of our target persona. In this lesson, we will introduce the concept of a list to add loops to our Terraform configuration. So, meaning that in this lesson we will get an overview on how to create multiple resources in one run. We will use loops and learn what the for each meta argument is. And finally, we will be creating multiple resources by iterating over a list. So how to create multiple resources? We learned that Terraform is declarative, meaning that we need to tell it explicitly what to do. So how can we now create multiple instances of a resource using a list? Of course, we could do a copy and paste, but I think, Christian, there is a better way to do this, right? Yeah, exactly. So there is a better way. Fortunately, folks at HashiCorp were aware of this requirement. And consequently, the HashiCorp configuration language contains the so-called meta arguments. These arguments are built into Terraform core and enable features that enhance the declarative setup. We already came across some example for meta arguments. used that depends on meta-argument to model explicit dependencies. That's not the only meta -arguments that's available. There are more. For example, Terraform offers the for each meta-argument that enables us to do iterations. This way, when looping over lists in the configuration, we do not have to do copy and paste, creating multiple resources, but we can iterate over a list in one resource configuration. Now, how does this look like in code? It's quite easy to implement such a loop. In the code sample, we want to iterate over a list of emergency admins and do a role collection assignment. So we want to assign different users to the same role collection, and we do not want to copy this resource block that you see on the screen for every user. You can see how we can do that in this example. Below the resource definition with the resource type and the resource address, we see that there is the for-each argument. This instructs Terraform to iterate over the list or to be more specific the set that is handed over to Terraform and execute the resource setup for each of the entries within this set. Usually you would define a list and here we have to use the two-set function in order to transform that into a set. That's just technical detail, which we will also see in the hands-on. The next question is, what happens during the execution? The for-each meta argument converts each entry of the list into a so-called each object with a key and a value. And this each object is then used to fill the username, as you can see in the last line. There we take the value of each object, which is the emergency admin, and assign it to the username. The remaining configuration is something that we already know, assigning a subaccount ID and the role collection name. Looks quite easy, right? So let's see how that works out. Yeah, that's actually what we will do now in our hands-on session. We will add a new variable that contains a list of users to add as emergency administrators for a subaccount. And we will enhance the Terraform configuration with the resource for assigning a role collection to iterate over the list of emergency users. So let's get our hand dirty. Okay, so we are back again in our Read Me and the MD file in the GitHub repository for Unit 4 and lesson 4. And let's have a look what we will do now to apply the loops. So the first thing we want to do is actually now assigning the users, the emergency administrators to a role collection, so meaning that we need a new resource, the roll collection assignment resource we see there that we need to have the subaccount ID in place, the role collection name, as well as the username. So, and also if we scroll down a bit, we also see as usual the required and optional parameters. But let's now see what we need to do. So first thing first, as Christian always says, we need to have a new variable in place for the subaccount emergency admins that we now copy and paste into the variables. file and importantly ensure that you are in the BTP directory so we add this over here. We also keep the default empty so that we are sure that we always add the right names. So secondly we need to add now some values for the emergency administrators over there. right so we just copy to emergency admins Jane and John Doe at test.com this is now a simple list so we just add two names to email addresses with comma separation so that's enough that's enough and then we need to actually add now the actual new resource yep there it is which into the main TF of the BTP folder again where we will be using the resource BTP subaccount role collection assignment along with this for each meta argument that you see here in line 51 that goes through all the newly added subaccount emergency admins for that variable we assign the subaccount ID then we assign the role collection name which is the subaccount administrator and the username that was the principle that also Christian described before is now going over the each dot value where we actually have then the actual email addresses. And we also have this two set function in order to convert the list that we have to a set because the key and value. Exactly because the for each just accept sets and maps. So we have to do that and yeah as we said then we use just as each object to go over that. And now as you can see we have now two emergency admins if you wouldn't have this argument you would have to copy this resource block twice if you add an emergency admin you have to remove it again add another one so that's super combo sum and with this you keep it really clean and the only file you need to touch is actually the terraform .tfvars file where you can either add or remove people from that list and I think that's all we had to do Yep, so let's do our... Usual drill, the format... We did some... There was some formatting that was fixed now, which is good. We validate again successful as usual. As expected. And now... That's most of the cases, right? It's most of the cases. Unit 4-4. Let's see what happens if we plan. We see now it's fetching again the current state. Yes. To know what... Yeah, we expect now to get two resources to be added. Yeah, because these are the two emergency administrators that we want to assign the role to. Yes. So one block of Terraform resource, but two resources to be added. For Jane and John Doe. For each, and it's Jane and John Doe, yeah. Perfect. You also see here already how things will be stored in the state. So, as we have only one resource with one address, of course it has to find a key to identify this resource in the state. And it uses the each object, the key of the each object, for identifying that one. So with that, we can now apply the changes. Already done. That was fast. So let's check if that really happened. In our global account, we can see it in the users. We should see Jane and John Doe. And they should have both. It's something we need to check. The subaccount administrator, yes. So for Jane, it's correct. And for John as well. As well. Yeah, that looks good. Now, of course, that's probably something that you wouldn't do in a productive setup with respect to directly assigning names. We saw usernames to a role collection, but you would probably go via group assignments. We saw it also in the documentation, because it's also an option there, right? The group name. Exactly. We just took this now for an easier ending. So that was just for demoing the for each argument, meta argument. So for the sake of completeness, we want to stress that there are more options to assign role collections, and this one is probably not the super best. best practice. So let's check now in our site here on the Read Me MD if we went through all that we wanted to show. Yes, except I think we are very tidy people, right? Yeah, absolutely. So we created now a lot of things together with you on your trial account, but why not now taking the power of Terraform to clean up everything that we have done? And get a clean trial account. What do you think? Yeah, I mean, we have everything in our configuration. So even if it's destroyed, we can build it up again and destroy it. Whatever you want to do. Now... Let's use that. Let's do that. There's just one thing that you, of course, have to keep in mind. You have to destroy things in the opposite direction as you created them. So we have to start from Cloud Foundry. First, delete the Cloud Foundry assets and then... Whoopsie. and then delete the BTP assets. Let's do this, come on. No longer talking. Let's switch to the Cloud Foundry folder first. And the command is easy. Terraform, destroy. Destroy. And this will now do basically the same as Apply because it's an alias for Apply minus Destroy. and it will now destroy all the stuff it also tells you what it will destroy how much it will be destroying and we say okay do it and I think it's important to mention that it's doing it as you said before in the in the opposite way right so it starts first with the resources with no dependencies right and then goes backwards it goes up the dependency tree it goes up the dependence So it does basically the same calculation as for the apply. It plans this execution plan. Just to... Yeah, vice versa, right? Exactly. So we have deleted the space and everything which is related to it. And now we switch to the BTP folder. And have more from there. And do also here a Terraform destroy. And it's also good that Terraform action. asks you if you really want to destroy. And I think it's always good to maybe think twice, right? If you really, really, really, really wanted to delete this. Just to be sure that you're on the safe side. So we have 11 resources to destroy, yeah. We create quite some stuff. So let's go for it. We are brave. We just do yes. And now we can see here the role collection assignment that we just did. It's deleting, it's destroying it, right? It's already started destroying the entitlements we see there. Now it's also destroying the subscription already. And let's wait a few seconds until this went through. So this will now definitely take a bit of time because we have the Cloud Foundry environment that also needs to be destroyed. We have the subaccount. That takes a bit. But what we can do, we can go to the global account and see that things are happening now already. So we go there. We should see that the subaccount is already being deleted. So deletion is in progress. Maybe something we don't have to show right now until this is done. We just wanted to show you that, yeah, really keeping the resources and also the subaccounts clean is pretty easy here with the destroy command and as you said the same way like we set it up now it's actually done we can delete it and we could now again terraform apply terraform apply to do this so that this is I think quite interesting especially also for sandbox environments if you try something out in your productive environment and you don't want to have things running over the weekend or running when the project is finished, it's super easy to get rid of everything. But with that said, I think we are done here with the hands-on. That's the case. We are back from the hands-on. What did we learn within this lesson? First, we learned the basic concept of meta-arguments that are available for Terraform resources and modules. They stretched the declarative boundaries of the language a bit, but in a good way. We specifically looked into the for each meta argument, which can be used to iterate over a list of values and create resources for each entry in that list. With that, we avoid copy-pacing the same resource definition all over the place. And with that, we are at the end of the lesson. Thanks for watching and looking forward to seeing you in the next and last lesson. Bye. Bye-bye.