(feature) automatic progressive rollout

[thomaspoignant]

Requirements

Be able to do a progressive rollout of a flag.
We need a way of automatically increase the percentage of users in the flag during the time.

What we want is to be able to set an initial percentage and a start date, and also a complete rollout date and percentage.
During between these 2 dates, the percentage will increase smoothly until reaching the complete rollout percentage.

[thomaspoignant]

If we have a rollout strategy configured, we ignore the field percentage because the rollout strategy is more important than the field.

The format of the rollout strategy should looks like :

test-flag:
  // ...
  rollout:
    progressive:
      percentage:
        initial: 10
        end: 80
      releaseRamp:
        start: 2021-03-20T00:00:00.10-05:00
        end: 2021-04-20T00:00:00.10-05:00

In that example

• before the releaseRamp.start date the percentage of the flag served will be 10%.
• between releaseRamp.start and releaseRamp.end we will have a progressive rollout between 10% and 80%.
• after releaseRamp.end we will use the percentage 80%.

rollout.progressive.percentage is not mandatory, if no set initial == 0 and end == 100.
rollout.progressive.releaseRamp is mandatory, if no set we will not use the rollout strategy.