Add "step-down" capabilities

Description of issue / feature request

Provide an optional configuration option to “step-down” the # of concurrent users based on some supplied rate, and after a defined amount of time after all locust users are hatched. Locust would continue to log the request data and statistics until there are 0 locust users by default.

Gherkin-style User Story (Perspective: Locust test-writer)

Feature: Step-down Capabilities As a user, I want to specify an expiration rate and duration, so that I can verify that hatched locust users are properly expired.

Scenario: Expiration Rate defined Given I start a standard locust execution And I supply a valid expiration rate And I supply a valid duration When I start the Locust swarm And the number of concurrent locust users reaches the defined maximum And the swarm has maintained the maximum number of locust users for duration seconds Then locust users expire as defined by the expiration rate And Locust continues to log data until reaching 0

Scenario: Expiration Rate not defined Given I start a standard locust execution And I supply a valid duration When I start the Locust swarm And the number of concurrent locust users reaches the defined maximum And the swarm has maintained the maximum number of locust users for duration seconds Then locust users expire as defined by the hatch rate And Locust continues to log data until reaching 0

Scenario: Duration not defined Given I start a standard locust execution And I supply a valid expiration rate When I start the Locust swarm And the number of concurrent locust users reaches the defined maximum And I click the Stop button Then locust users expire as defined by the expiration rate And Locust continues to log data until reaching 0

[heyman]

It could be conceivable that the rate of decline at the end of a load test is important as items in queues need to be processed after the peak.

That’s true. If and when we implement support for steps in the ramping up of locust users (or more general scenarios), we should also make sure that it also supports stepping down. There is an open issues for this at #1001.

[iramisvalentincapco]

@micsjo That would be a separate feature which would build upon the functionality that this feature would offer.