Description
Key information
- RFC PR: https://github.com/awslabs/aws-lambda-powertools-python#494
- Related issue(s), if known:
- Area: Utilities - AppConfig
- Meet tenets: (Yes/no)
- Approved by: @heitorlessa
- Reviewed by: @pcolazurdo
Maintainers Note: Update RFC after docs have been created as implementation was improved
Summary
[summary]: Simplify the usage of feature toggles with AppConfig. Take it to the next level with a rule engine that provides calculated values of feature toggles according to input context.
Motivation
Why are we doing this? What use cases does it support? What is the expected outcome?
App config is great but it's very raw/barebones. This feature will encourage people to use AppConfig.
I'd like to build a feature toggles on top the current app config utility.
Proposal
Build a simple feature toggle rule engine. The rules will be part of the JSON schema that is uploaded to AppConfig. The rule engine will use existing powertools utility to load and parse the json from AppConfig.
It will provide a simple function (same API as launch darkly support) for getting a feature toggle by name. The function will also receive a context dict which will be matched against a set of rules. The feature will have a default boolean value. However, if the context data matches a rule in the schema JSON, the returned value will be the value that is defined in the matched rule.
This can allow you to have a feature toggle turned off by default but turning it on for a specific user or customer in a specific region etc.
The rules will accept any key/value context.
Supported actions can be equals, starts with, regex match , endswith, in a list and many more. It's very easy to extend the engine.
An example rule: 'if customer_name' equals coca cola and username starts with 'admin' , trigger the feature on. For other cases, the feature is off. See configuration language below.
This type of API will take appconfig to the next level. It's very much barebones at the moment.
If this feature should be available in other runtimes (e.g. Java, Typescript), how would this look like to ensure consistency?
It can be done in other languages, it's a very simple rule engine that I've already written in Python.
User Experience
How would customers use it?
conf_store: ConfigurationStore = ConfigurationStore(
environment='test_env',
service='test_app',
conf_name="test_conf_name",
cache_seconds=600,
)
toggle: bool = conf_store.get_feature_toggle(feature_name='my_feature', rules_context={'customer_name': 'coca-cola', 'username': 'abc'}, default_value=False)
The default value parameter in the API is the default value to return if the feature doesn't exist in the json schema.
Any configuration or corner cases you'd expect?
Example configuration:
{
'log_level': 'DEBUG',
'features': {
'my_feature': {
'default_value':
'False',
'rules': [
{
'name':
'set the toggle on for customer name 666 and username abc ',
'default_value':
True,
'restrictions': [
{
'action': 'EQUALS',
'key': 'customer_name',
'value': 'coca-cola',
},
{
'action': 'EQUALS',
'key': 'username',
'value': 'abc',
}
]
},
]
}
}
}
Drawbacks
Current solution has support for only boolean values for feature toggles. This can be of course expanded if required rather easily.
Why should we not do this?
dont see a reason not to :)
Do we need additional dependencies? Impact performance/package size?
Solution can be based upon pydantic (very easy) or regular json parsing.
Rationale and alternatives
Alternative is to use a third party tool (which is not free) like Launch Darkly.
-
What other designs have been considered? Why not them?
You can use Launch Darkly. However, this solution is very simple and provides the same client side API that launch darkly provide with AWS AppConfig. -
What is the impact of not doing this?
Unresolved questions
Optional, stash area for topics that need further development e.g. TBD