Selecting multiple configs from a Config Group

 

Problem

In some scenarios, one may need to select multiple configs from the same Config Group.

Solution

Use a list of config names as the value of the config group in the Defaults List or in the command line.

Example

In this example, we configure a server. The server can host multiple websites at the same time.

Config directory

├── config.yaml
└── server
    ├── apache.yaml
    └── site
        ├── amazon.yaml
        ├── fb.yaml
        └── google.yaml

config.yaml

defaults:
  - server/apache

server/apache.yaml

defaults:
  - site:
    - fb
    - google

host: localhost
port: 443

server/site/amazon.yaml

amazon:
  domain: amazon.com

server/site/fb.yaml

fb:
  domain: facebook.com

server/site/google.yaml

google:
  domain: google.com

Output:

$ python my_app.py

server:
  site:
    fb:
      domain: facebook.com
    google:
      domain: google.com
  host: localhost
  port: 443

Override the selected sites from the command line by passing a list. e.g:

$ python my_app.py 'server/site=[google,amazon]'

server:
  site:
    google:
      domain: google.com
    amazon:
      domain: amazon.com
  host: localhost
  port: 443

Overriding packages

You can relocate the package of all the configs in the list. e.g:

server/apache.yaml

defaults:
  - site@https:
    - fb
    - google

$ python my_app.py

server:
  https:
    fb:
      domain: facebook.com
    google:
      domain: google.com

When overriding the selected configs of config groups with overridden packages you need to use the package. e.g:

$ python my_app.py server/site@server.https=amazon

server:
  https:
    amazon:
      domain: amazon.com
  host: localhost
  port: 443

Implementation considerations

A nested list in the Defaults List is interpreted as a list of non-overridable configs:

server/apache.yaml

defaults:
  - site:
    - fb
    - google

Equivalent to

defaults:
  - site/fb
  - site/google

All default package for all the configs in server/site is server.site. This example uses an explicit nesting level inside each of the website configs to prevent them stepping over one another:

server/site/amazon.yaml

amazon:
  ...