The Circuit Breaker pattern is a design pattern used in software development to improve the stability and resilience of a system. In a Rails application, using a circuit breaker can prevent your system from making unnecessary requests to external services when they are known to be failing. This pattern can be particularly useful when your Rails application interacts with external APIs, databases, or other microservices.
The Basics of the Circuit Breaker Pattern
Think of a circuit breaker in electrical systems. It trips or “breaks” the circuit when there’s too much current, preventing potential damage. Similarly, in software, a circuit breaker “trips” when certain conditions are met, usually after detecting that a particular service is unavailable or failing.
Here are the three primary states of a circuit breaker:
- Closed: Everything is functioning as expected. Requests are made to the external service.
- Open: The external service is down or unresponsive. Requests are not made; instead, failures are returned immediately.
- Half-Open: After a predetermined amount of time, the circuit breaker allows some requests to check if the service has recovered. If it’s stable, the state returns to Closed; otherwise, it remains Open.
Implementing a Simple Circuit Breaker in Rails
Let’s design a simple circuit breaker without relying on any gems or plugins.
Model the Circuit Breaker
attr_accessor :failure_count, :state, :last_failed_time
FAILURE_THRESHOLD = 5
HALF_OPEN_TIME = 60 # seconds
@failure_count = 0
@state = :closed
@last_failed_time = nil
raise "Service Unavailable"
make_request if Time.now - last_failed_time >= HALF_OPEN_TIME
# Replace with your actual request to an external service
response = ExternalService.call
raise "Service Error"