Half Open State

[drgarcia1986]

To follow the Nygard circuit breaker pattern we need to create the half-open state on the circuit breaker. :

There is now a third state present - half open - meaning the circuit is ready to make a real call as trial to see if the problem is fixed.

source

[rafa-acioly]

I would like to address this issue but i have a few questions first, on the source that you provide there are a few things that i need more opinion about.

1. The parameter last_failure_time

I was thinking that we can use the TTL value from the request_cache_key, this way we can compare this TTL value with the parameter circuit_timeout or we add a new parameter to use this value on a different cache key.

2. The half-open state

The source text suggest two approaches:

Set the half-open state when the current state is open and a time is reached, example:

• The circuit is open and it has been open for 1 minute, now we can "try" to call the method again, this would change the circuit to half-open, if the request succeed we close the circuit, otherwise we keep it open.

Set the half-open state based on the percentage of errors:

A more sophisticated approach might look at frequency of errors, tripping once you get, say, a 50% failure rate.

This one is a little confuse to me, it says that the half-open state will be use when the errors percentage reach 50%, this means that the we will only try 50% of the requests on purpose and fail the remain 50%?

About the implementation of this percentage errors, it will only available on the PercentageFailuresRule class? or we need to implement it for every rule?