Extracting Substrings from a List of Strings in Terraform

Learn how to effectively extract `source` and `destination` VNet names from a list of VNet peering details in Terraform, and streamline your network configurations.
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Extracting Substrings from a List of Strings in Terraform

When working with virtual networks in Azure, you often encounter the need to parse and manipulate strings, especially when dealing with resources like VNet peering. If you're faced with a list of VNet peering details and need to separate them into source and destination networks, you're in the right place! In this guide, we'll explore how to extract specific substrings using Terraform, making your configurations more manageable and organized.

The Challenge

Imagine you have the following list of VNet peering names:

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

From this, you want to extract two separate lists:

Source VNets should contain: ["vnet1", "vnet1", "vnet4"]

Destination VNets should contain: ["vnet2", "vnet3", "vnet5"]

The goal is to achieve this through Terraform’s configuration language efficiently.

Solution Breakdown

Here’s how you can extract the desired source and destination strings using Terraform's built-in functions. We’ll utilize the split function to parse each string and the for expression to iterate over the list. Follow these steps:

Step 1: Define Your Variables

First, you'll want to define your list of VNet peers within the locals block:

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

Step 2: Extract Source and Destination VNets

Next, use the split function to separate the names at the "to" delimiter. You will create two separate lists as follows:

Creating the Source List:

Use a for loop to iterate over each element in local.Peer, splitting at "to" and taking the first element (source):

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

Creating the Destination List:

Similarly, take the second element from the split for the destination:

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

Complete Code Example

Here’s the complete example wrapped up in a locals block:

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

This simple yet powerful snippet will effectively parse your VNet peering details into their respective lists of source and destination values.

Conclusion

Managing Azure network resources such as VNet peering can be streamlined significantly by effectively using Terraform’s string handling capabilities. By understanding how to utilize the split function and list comprehensions, you can extract necessary information from complex strings effortlessly.

Now that you have the tools to extract substrings, you can enhance your Terraform configurations, making them cleaner and easier to maintain. Happy coding!