How to Use a Non-unique Key in Terraform Resource Loop to Create Unique Resources

Learn how to overcome the challenges of using non-unique keys in Terraform by creating a solution that enables you to generate unique resources, particularly for DNS records.
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This video is based on the question https://stackoverflow.com/q/66256261/ asked by the user 'Afraz' ( https://stackoverflow.com/u/2212140/ ) and on the answer https://stackoverflow.com/a/66270363/ provided by the user 'Marcin' ( https://stackoverflow.com/u/248823/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use a Non-unique Key in Terraform Resource Loop to Create Unique Resources

When working with Infrastructure as Code (IaC) tools like Terraform, one common challenge developers face is managing resources that have non-unique keys. This is particularly critical when defining DNS records for a domain. If you've tried setting up multiple records with the same key (like @ in DNS), you may have encountered issues where only the last defined record is created. In this guide, we will explore a solution to elegantly handle this scenario.

The Problem

You might find yourself needing to create multiple DNS records for a domain using a generic Terraform module. It's common to want to define multiple records of the same type but with different values, such as:

[[See Video to Reveal this Text or Code Snippet]]

In the setup above, when you loop over txt_records, only one of the records (in this case, txt-foobar2) will be created because keys must be unique. Clearly, this isn't the desired outcome. So, how can we ensure both values get created?

The Solution

Step 1: Redefine Your Structure

Instead of using a map with non-unique keys, consider redefining your txt_records variable as a list of maps. Each map can contain a single key-value pair ensuring uniqueness, as shown below:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Flattening the Record Structure

Once you've restructured your records, you’ll need to flatten them into a more manageable format for Terraform to iterate over. Use the following local variable to achieve this:

[[See Video to Reveal this Text or Code Snippet]]

This local declaration transforms your input into a structure that is suitable for looping. The output, local.txt_records_flat, will look similar to:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Implement the Resource Block

Now that you have a well-structured collection, you can implement your resource block like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By restructuring your Terraform variables and utilizing the merging technique, you can effectively create multiple DNS records with non-unique keys without losing any entries. This approach not only resolves the issue but also enhances the flexibility and maintainability of your Terraform modules.

Remember, tackling the problem of non-unique keys requires a thoughtful approach to your data structures, but with Terraform's powerful looping capabilities, you can navigate through these challenges effectively.

If you are interested in exploring more Terraform solutions or have any questions about implementing this solution, feel free to reach out!

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