Terraform data sources provide information on existing resources. This is handy for configuration dependencies that exist across Terraform plans.
In my scenario, I wanted to attach an Amazon Web Services (AWS) Virtual Private Cloud (VPC) to an existing Transit Gateway. I needed to use a data source to pull the Transit Gateway’s id value. Using the assigned AWS tags seemed like a viable solution.
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Digging In Further
Below is an example of my configuration in AWS:
I could not find a clear description of how to filter a data source by the AWS tag key/value pairs. However, the aws_instance data source provided me a clue.
The key/value pair can be provided using the syntax below:
- Key: The
nameparameter uses the syntaxtag:<key>to provide the AWS key name. - Value: The
valuesparameter provides the AWS key value.
The full working Terraform code snippet is shown below:
data "aws_ec2_transit_gateway" "tgw" {
filter {
name = "tag:Name"
values = ["wahlnetwork-tgw-prod"]
}
}Now that I had the Transit Gateway’s id value, I was able to supply it to a resource object further along in the plan.
resource "aws_ec2_transit_gateway_vpc_attachment" "vpc-tgw-attachment" {
subnet_ids = [aws_subnet.priv01.id, aws_subnet.priv02.id]
transit_gateway_id = data.aws_ec2_transit_gateway.tgw.id
vpc_id = aws_vpc.vpc.id
}
}At least now I have written down the filter syntax for an AWS tag for the next time I need it!
Next Steps
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