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

Implementation considerations

The following two forms compose the same output:

server/apache.yaml

defaults:
  - site:
    - fb
    - google

Composes like

defaults:
  - site/fb
  - site/google

Use the nested list form when you want to override the group later with 'server/site=[...]'.

To delete one of these non-overridable entries from the command line, use the exact config path, for example ~server/site/fb.

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:
  ...