Using examples and demos, this talk will walk through leveling up HCL knowledge from level 2 to level 7. You'll see examples of using functions, variables, and polymorphism to work through a "configuration DSL" built using HCL. The example will be fun and simple, but the techniques should be generalizable to a lot of problems.

3. Intermediate HCL
Configuration
Languages in HCL2
Russell Rollins
Release Engineer at HashiCorp
russell@hashicorp.com | @russell_rollins
Copyright © 2019 HashiCorp

4. CODE EDITOR
project = "example-project"
deploy_id = env.BUILD_ID
artifact {
artifact_type = "quay_repo"
config {
repo = project.name
tag = project.deploy_id
}
}

5. Domain Specific Configuration Language
YAML
▪ Schemaless
▪ Variables loosely supported using
anchors or an external templating
engine.
▪ Functions loosely supported using an
external templating engine.
HCL
▪ Shemaful? Schema-having? It has a
schema.
▪ Variables supported as a first class
citizen.
▪ Functions supported as a first class
citizen.

6. An Analogy
In language, people in certain fields or social groups use jargon, slang, or
argot. These are less general than normal language, but can be used to
densely pack information using shared context.

7. Concretely, Creating DSCLs
Variables
Variables allow dynamism in configuration. For instance, reading from the
environment or another file. 12 Factor HCL. We’ll use this to support
env.CAT_SOUND
Functions
Functions create even more powerful and flexible configurations. Combine with
string interpolation to build complex configuration. We’ll use this to build
random()
Partial Decoding + Polymorphism
Partial Decoding is a concept in HCL that allows it to be “self referential” where
decoding decisions can be made based on other configuration. We’ll use this to
support type = “cat” and type = “dog”

8. Demo
If I have listen to myself ramble on anymore I’m going to get
bored.

9. Call to Action
Go convert some services to consume HCL for configuration, you’ll learn
more about your tool’s domain and about HCL.

10. Links
https://github.com/RussellRollins/pet-sounds
https://github.com/hashicorp/hcl/tree/v2.3.0
https://twitter.com/mitchellh/status/1016475256498761728