App and Role Layering
Concept
Terraspace also has the concept of TS_APP and TS_ROLE layering. This is helpful when you want to reuse the same stack for multiple apps. You can deploy it with App and Role layering. Some possible examples are AWS CodeBuild and CodePipeline resources. When TS_APP is set, app-scoped layers are activated. And when TS_ROLE is set, role-scoped layers are also activated.
Why the App and Role Layers?
Infrastructure can be sometimes infra-centric or app-centric. Some examples:
- infra-centric: Multiple apps typically share infra-centric infrastructure components. VPC networks, EKS, AKS, GKE Clusters.
- app-centric: App-centric infrastructure focuses on specific apps. For example, build jobs like AWS CodeBuild, Azure Container Service, Google CloudBuild, and pipelines.
With app-centric infrastructure, one option is to create separate stacks. Example:
app/stacks/app1
app/stacks/app2
# and
terraspace up app1
terraspace up app2
Or you can create a “standard” app stack and then override configurations with the app-scoped layers. Example:
app/stacks/app
# and
TS_APP=1 terraspace up app
TS_APP=2 terraspace up app
The same stack is reuse for multiple apps. The differences can be handled with different tfvar layered files. The pro is that it’s very DRY. The con is that, if an app strays too far away from the “standard” stack code, the code can get complex. In which case, it may make sense to create a new dedicated stack.
App and Role Layers
First set TS_APP and TS_ROLE. Example:
export TS_APP=app1
export TS_ROLE=deploy
Now build a stack.
$ terraspace build demo
Building .terraspace-cache/us-west-2/dev/stacks/demo
...
config/stacks/demo/tfvars/deploy.tfvars
config/stacks/demo/tfvars/deploy/base.tfvars
config/stacks/demo/tfvars/deploy/dev.tfvars
config/stacks/demo/tfvars/deploy/us-west-2.tfvars
config/stacks/demo/tfvars/deploy/us-west-2/base.tfvars
config/stacks/demo/tfvars/deploy/us-west-2/dev.tfvars
config/stacks/demo/tfvars/app1.tfvars
config/stacks/demo/tfvars/app1/base.tfvars
config/stacks/demo/tfvars/app1/dev.tfvars
config/stacks/demo/tfvars/app1/us-west-2.tfvars
config/stacks/demo/tfvars/app1/us-west-2/base.tfvars
config/stacks/demo/tfvars/app1/us-west-2/dev.tfvars
config/stacks/demo/tfvars/app1/deploy.tfvars
config/stacks/demo/tfvars/app1/deploy/base.tfvars
config/stacks/demo/tfvars/app1/deploy/dev.tfvars
config/stacks/demo/tfvars/app1/deploy/us-west-2.tfvars
config/stacks/demo/tfvars/app1/deploy/us-west-2/base.tfvars
config/stacks/demo/tfvars/app1/deploy/us-west-2/dev.tfvars
Tip: Seeing Layering Clearly
To see the layers being used, use the config.layering.show option.
config/app.rb
Terraspace.configure do |config|
config.layering.show = true
end
This will show found layers, which is what you want to see most of the time. To see all possible layers, see: Debugging Layering Docs.
Stick to a Few
Since layering is so powerful, you want to choose a few layers that make sense for your team and stick to them.
$ export TS_APP=app1
$ export TS_ROLE=deploy
$ terraspace build demo
Building .terraspace-cache/us-west-2/dev/stacks/demo
config/stacks/demo/tfvars/base.tfvars
config/stacks/demo/tfvars/dev.tfvars
config/stacks/demo/tfvars/app1/base.tfvars
config/stacks/demo/tfvars/app1/dev.tfvars
