App and Role Layering

Concept

Lono also has the concept of LONO_APP and LONO_ROLE layering. This is helpful when using Lono and CloudFormation to deploy app-central resources. Some possible examples are AWS CodeBuild and CodePipeline resources. When LONO_APP is set, app-scoped layers are activated. And when LONO_ROLE is set, role-scoped layers are also activated.

Why the App and Role Layers?

First, Lono is a CloudFormation framework. As such, it is mainly used to provision AWS Cloud infrastructure. Infrastructure can be sometimes env-centric or app-centric, though. Some examples:

  • env-centric: VPC networks, ECS clusters, EKS clusters. Can also be thought of as infra-centric.
  • app-centric: CodeBuild projects, CodePipeline pipelines. These resources can be specific to apps.

Multiple apps typically share env-centric infrastructure components. App-centric infrastructure focuses on specific apps.

With app-centric infrastructure, one option is to create separate blueprints. Example:

app/blueprints/app1
app/blueprints/app2
# and
lono up app1
lono up app2

Or you can create a “standard” app blueprint and then override configurations with the app-scoped layers. Example:

app/blueprints/app
# and
LONO_APP=1 lono up app
LONO_APP=2 lono up app

Essentially, the same blueprint is reuse for multiple apps. It’s DRY. However, if an app strays too far away from the “standard” blueprint code, it may make sense to create a new dedicated blueprint.

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. First set LONO_APP and LONO_ROLE.

export LONO_APP=app1
export LONO_ROLE=deploy

Here are some layers that you can use now.

config/blueprints/demo/params/app1/base.env
config/blueprints/demo/params/app1/dev.env
config/blueprints/demo/params/app1/deploy/base.env
config/blueprints/demo/params/app1/deploy/dev.env

Shown as a tree

config/blueprints/demo/params/
└── app1
    ├── base.env
    │── dev.env
    └── deploy
        ├── base.env
        └── dev.env

Seeing Layers Clearly

To see the layers being used, use the config.layering.show option.

config/app.rb

Lono.configure do |config|
  config.layering.show = true
end

With that turned on, you’ll see the found layers that will be used:

$ export LONO_APP=app1
$ export LONO_ROLE=deploy
$ lono build demo
Building parameters
    config/blueprints/demo/params/app1/base.env
    config/blueprints/demo/params/app1/dev.env
    config/blueprints/demo/params/app1/deploy/base.env
    config/blueprints/demo/params/app1/deploy/dev.env
    output/demo/params.json

This will only show found layers, which is what you want to see most of the time. To see all possible layers, see: Debugging Layering Docs.