travetto: Config

The config module provides support for loading application config on startup. Configuration values support all valid yaml constructs.

Resolution

Config loading follows a defined resolution path:

1. Load framework module configurations. Defines general configuration that should be easily overridden.

node_modules/@travetto/<module>/config/*.yml

2. Load local application configurations

config/*.yml

3. Load environment specific configurations as defined by the values in process.env.ENV

process.env.ENV=<val1>,<val2>...

would load

env/<val1>.yml
env/<val2>.yml

4. Read startup configuration from process.env to allow for overriding any values. Because we are overriding ayaml based configuration we need to compensate for the differences in usage patterns. Generally all environment variables are passed in as UPPER_SNAKE_CASE. When reading from process.env we will map UPPER_SNAKE_CASE to upper.snake.case, and will attempt to match by case-insensitive name.

Example Resolution

A more complete example setup would look like:

config/database.yml

database:
  host: localhost
  port: 9423
  creds:
    user: test
    password: test

env/prod.yml

database:
  host: prod-host-db
  creds:
    user: admin-user

with environment variables

ENV=prod
DATABASE_PORT=1234
DATABASE_CREDS_PASSWORD=<secret>

At runtime the resolved config would be:

database:
  host: prod-host-db
  port: 1234
  creds:
    user: admin-user
    password: <secret>

Reading

The module provides a decorator, @Config that allows for classes to automatically be bound with config information on post construction. The decorator will install a postConstruct method if not already defined, that allows actually performs the binding of configuration.

The decorator takes in a namespace, of what part of the resolved configuration you want to bind to your class. Given the following class

@Config('database')
class DBConfig {
  private host: string;
  private port: number;
  private creds = {
    user: '',
    password: ''
  };
}

And the corresponding config file

database:
  host: localhost
  port: 9423
  creds:
    user: bob
    password: bobspw

The instance of DBConfig would be equivalent to:

{
  host: 'localhost',
  port: 9423,
  creds : {
    user: 'bob',
    password: 'bobspw'
  }
}