Tfvars: Dynamic
The tfvars files get processed by ERB templating, providing some dynamic control.
Example 1: output
A useful helper is output, it allows you to grab the output value from another stack and use it as an input variable for another stack.
config/stacks/demo/tfvars/base.tfvars:
vpc_id = <%= output("vpc.vpc_id")" %>
Terraspace also uses this information to build the dependency graph and deploys the dependent stacks in the correct order with terraspace all up. Related useful docs:
Example 2: General
One example is maybe you want to use TS_ENV in your variables dynamically with the ERB.
config/stacks/demo/tfvars/base.tfvars:
name = "<%= Terraspace.env %>-instance"
Then:
TS_ENV=dev terraspace build demo
Results in:
name = "dev-instance"
And:
TS_ENV=prod terraspace build demo
Results in:
name = "prod-instance"
Example 3: TS_EXTRA Example
Here’s an example with the TS_EXTRA env var in a tfvars file.
config/stacks/server/tfvars/base.tfvars:
name = "<%= Terraspace.extra %>-server"
So:
TS_EXTRA=bob terraspace up server
Results in:
name = "bob-server"
So:
TS_EXTRA=kevin terraspace up server
Results in:
name = "kevin-server"
Recommendation
Using ERB in the tfvar files is a pretty clean way of adding a little bit of dynamism. A good thing about the approach is that it keeps your Terraform module code purely native. When possible, it is recommended to use the ERB power that terraspace provides responsibly though.
