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GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. This behavior is unfortunately intended for the moment.
The ability to use data resource attributes in count didn't make it into 0. Is there a known mechanism by which I could work around the issue? My only thoughts would be possibly encapsulating the data source in a module, and passing it's response as an output used by the resources, but I'm not sure if that would work, and haven't yet tested it.
Outside of that, I would have to just do the legwork outside of terraform and render values in, basically replicated the data source outside of terraform, which obviously makes me sad.
MarsuperMammal it looks like what you were trying to do here is create one EC2 instance for each availability zone available to your account. Assuming I understood correctly, a possible workaround could be to use an autoscaling group, in which case Terraform sees only one resource the autoscaling group and AWS itself creates the appropriate number of instances. Here's an example of what I mean, though I didn't test this yet since I don't have my AWS credentials to hand at the moment:.
Dynamic count that is, a count that isn't known until after we've built and walked the configuration graph was originally intended as part of the data sources feature, but it proved more complex to implement than originally thought and so it was deferred for now.
The reason for the complexity is that there is a bit of a chicken-and-egg problem in that we currently do the "expand" operation turning a single configuration block into a set of objects based on the count argument during graph construction, which happens before we "walk" the graph. Data source fetching happens during the "refresh" phase, which is run on an already-constructed graph where it's too late for us to dynamically populate the count. To fix this requires some reorganization of Terraform's workflow, the design for which is not yet obvious.
I was actually mistaken when I said there was an open ticket for this in my last comment. I forgot that this feature was originally being tracked in the data source issue, but that was closed with a reduced scope already.
I expect we'll open a new ticket for this once a more concrete design is devised, but for now I suppose this ticket will serve to represent the missing feature. The use of the ec2 resource leveraging the data source for count was merely a simple example resource. The idiom itself has desired implementations in many places, where less clear solutions, such as using autoscaling groups, aren't available.This is Part 2 of the Comprehensive Guide to Terraform series.
The official Terraform Getting Started documentation does a good job of introducing the individual elements of Terraform i. In particular, we will provision several servers on AWS in a cluster and deploy a load balancer to distribute load across that cluster.
Note that all the code samples are written for Terraform 0. Terraform can provision infrastructure across many different types of cloud providers, including AWS, Azure, Google Cloud, DigitalOcean, and many others.
When you first register for AWS, you initially sign in as the root user. This user account has access permissions to everything, so from a security perspective, we recommend only using it to create other user accounts with more limited permissions see IAM Best Practices.
You MUST save these immediately, as they will never be shown again. We recommend storing them somewhere secure e. To be able to use Terraform for the examples in this blog post series, add the following permissions learn more about Managed IAM Policies here :. Follow the instructions here to install Terraform. In order for Terraform to be able to make changes in your AWS account, you will need to configure the AWS credentials for the user you created earlier.
There are several ways to do this see A Comprehensive Guide to Authenticating to AWS on the Command Lineone of the easiest of which is to set the following environment variables:. Terraform code is written in a language called HCL in files with the extension.
It is a declarative language, so your goal is to describe the infrastructure you want, and Terraform will figure out how to create it. Terraform can create infrastructure across a wide variety of platforms, or what it calls providersincluding AWS, Azure, Google Cloud, DigitalOcean, and many others.
You can write Terraform code in just about any text editor. The first step to using Terraform is typically to configure the provider s you want to use. Create a file called main. This tells Terraform that you are going to be using the AWS provider and that you wish to deploy your infrastructure in the us-east-2 region AWS has data centers all over the world, grouped into regions and availability zonesand us-east-2 is the name for data centers in Ohio, USA. For each provider, there are many different kinds of resources you can create, such as servers, databases, and load balancers.
Add the following code to main. The general syntax for a Terraform resource is:. In a terminal, go into the folder where you created main. The terraform binary contains the basic functionality for Terraform, but it does not come with the code for any of the providers e.
By default, the provider code will be downloaded into a. Now that you have the provider code downloaded, run the terraform plan command:. The plan command lets you see what Terraform will do before actually doing it. This is a great way to sanity check your changes before unleashing them onto the world.
In the output above, you can see that Terraform is planning on creating a single EC2 Instance and nothing else, which is exactly what we want. To actually create the instance, run the terraform apply command:. To add one, you can add a tag to the EC2 instance:. Run terraform apply again to see what this would do:. The next step is to run a web server on this Instance. How do you get the EC2 Instance to run this script? You need to do one more thing before this web server works.
To allow the EC2 Instance to receive traffic on portyou need to create a security group :. For example, a CIDR block of The CIDR block 0.One of the things I do as part of Eiara is write a lot of Terraforman infrastructure definition language, to provide a sensible baseline cloud instantiation of infrastructure and resources.
Lots and lots and lots of JSON. Of course, nothing could go wrong with a rogue template here, but I digress. But, we can write content out to disk, and check that our JSON blobs are working as expected. Interestingly, files that are rendered by the Terraform template system have access to the full range of functions provided by the Terraform interpolation engine. This means that you can use the file function from inside a template file. Back to trying to render my JSON.
The first thing I tried was just to plug a list in, and try to render it inside the template, much like this. However, if we use join ",", var. Well, that breaks. We have the jsonencode function, which returns blocks of JSON. We can render our list arbitrarily!
But the goal here is to drop a list of rendered blobs of JSON into our template. How does that hold up with jsonencode? This is obviously a bit of a weird, complex case. Fun with Terraform Template Rendering One of the things I do as part of Eiara is write a lot of Terraforman infrastructure definition language, to provide a sensible baseline cloud instantiation of infrastructure and resources.
Straightforward, right? But, I digress. What about a nested map?
How to use Terraform variables
Will that work? The indentation is a bit off, but Python can read it! Complexity This is obviously a bit of a weird, complex case. And that feels right.This is Part 5 of the Comprehensive Guide to Terraform series. In previous parts, we explained why we picked Terraformintroduced the basic syntax and features of Terraformdiscussed how to manage Terraform stateand showed how to create reusable infrastructure with Terraform modules.
Terraform is a declarative language. However, without access to a full programming language, certain types of tasks become more difficult in a declarative language.Terraform : AWS - How to build reusable terraform modules with example
Note that all the code samples are written for Terraform 0. Terraform offers several different looping constructs, each intended to be used in a slightly different scenario:. Now that you have this user, you can create and manage all future IAM users with Terraform.
Consider the following Terraform code:. What if you wanted to create three IAM users? Terraform does not have for-loops or other traditional procedural logic built into the language, so this syntax will not work. However, every Terraform resource has a meta-parameter you can use called count. Therefore, you can create three IAM users as follows:.
One problem with this code is that all three IAM users would have the same name, which would cause an error, since usernames must be unique. If you had access to a standard for-loop, you might use the index in the for loop, ito give each user a unique name:.
To accomplish the same thing in Terraform, you can use count. If you combine count. If you were using a general-purpose programming language with loops and arrays, you would configure each IAM user to use a different name by looking up index i in the array var. In Terraform, you can accomplish the same thing by using count plus two new tricks.
The first trick is to use array lookup syntax to look up elements in an array at a given index. This syntax is identical to what you see in most other programming languages:. As you can probably guess, the length function returns the number of items in the given LIST. It also works with strings and maps.Variables in Terraform are a great way to define centrally controlled reusable values.
The information in Terraform variables is saved independently from the deployment plans, which makes the values easy to read and edit from a single file. You can use the general information about the variables as a quick cheat-sheet but the examples are a direct continuation to our Terraform beginners article.
An Introduction to Terraform
Terraform supports a few different variable formats. Depending on the usage, the variables are generally divided into inputs and outputs. The input variables are used to define values that configure your infrastructure. Output variables, in contrast, are used to get information about the infrastructure after deployment. These can be useful for passing on information such as IP addresses for connecting to the server. Input variables are usually defined by stating a name, type and a default value.
However, the type and default values are not strictly necessary. Terraform can deduct the type of the variable from the default or input value. Variables can be predetermined in a file or included in the command line options. As such, the simplest variable is just a name while the type and value are selected based on the input. The input variables, like the one above, use a couple of different types: strings, lists, maps, and boolean.
Here are some examples of how each type are defined and used. Strings mark a single value per structure and are commonly used to simplify and make complicated values more user-friendly. Below is an example of a string variable definition. A string variable can then be used in resource plans.
Surrounded by double quotes, string variables are a simple substitution such as the example underneath. Another type of Terraform variables lists.
I am trying to generate a bunch of files from templates - I need to replace the hardcoded 1 with the count. An example below. Learn more. Ask Question. Asked 1 year, 11 months ago. Active 1 year, 11 months ago. Viewed 11k times. Active Oldest Votes. Opster Elasticsearch - Nathan Opster Elasticsearch - Nathan 6, 3 3 gold badges 22 22 silver badges 39 39 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Post as a guest Name. Email Required, but never shown. The Overflow Blog. Socializing with co-workers while social distancing. Podcast Programming tutorials can be a real drag. Featured on Meta. Community and Moderator guidelines for escalating issues via new response….Terraform is a fantastic tool for deploying resources.
You type a resource in your script, run terraform apply and voila! You have infrastructure! But, the idea of having to add a resource block for every single resource can be daunting and really clutter your scripts. What if there was a way to multiply similar resources using one parameter?
By golly, there is! For this guide to be useful, it is expected that you already know how to write Terraform scripts and deploy Terraform resources. Alright, that is just ugly. These will append a random string of digits to each bucket in order to ensure entropy. All S3 buckets in AWS must have names that are globally unique. Next, we deploy two S3 buckets. So, if you run a terraform apply, you should see both buckets created.
All is well and good… or is it? Of course, it does! But, then, instead of just going straight to the. That asterisk lets Terraform know that we are going to be iterating through multiple items. After that, we add our dec, then we get to the next weird part.
Terraform tips & tricks: loops, if-statements, and gotchas
We have to choose which random ID to use. The [count. Instead of specifying these statically, we just use [count. Perform a terraform apply and see how it goes! I bet it went well! What we want to do is output a comma-delimited list of bucket names. That looks simple enough. The first thing, other than the join that you may notice, is the absence of [count. So, what we have is perfectly fine.