Data sources are very similar to regular resources. The main difference is that they are read-only. You can't always (actually, far from it) have the complete infrastructure in your Terraform templates. It is often the case that some resources already exist and you don't have much control over them. You still need to use them inside your Terraform templates, though. That's when data sources become handy.
In the Terraform documentation for each provider, there is a list of data sources (if any are available). They are configured almost the same as regular resources, with some differences.
Let's try them out in our template. There is a feature named VPC Peering in AWS. It allows the connection of two different VPCs in a way that instances inside both can talk to each other. We could have a VPC provided by another team, responsible for...
