Circuit Breaker

The circuit breaker prevents cascading failures by detecting backend outages and failing fast instead of waiting for timeouts.

States

State	Behavior
Closed	Normal operation. Requests pass through. Failures are counted.
Open	Fail fast. Raises CircuitOpenException immediately.
HalfOpen	Probe. Allows half_open_max_calls requests through to test recovery.

Configuration

Session.configure do |config|
  config.circuit_breaker_enabled = true
  config.circuit_breaker_config = Session::CircuitBreakerConfig.new(
    failure_threshold: 5,           # Failures before opening
    reset_timeout: 30.seconds,      # Time before probing recovery
    half_open_max_calls: 1          # Probe requests in half-open state
  )
end

Properties

Property	Type	Default	Description
circuit_breaker_enabled	Bool	false	Enable circuit breaker
failure_threshold	Int32	5	Consecutive failures before opening
reset_timeout	Time::Span	30.seconds	Wait time before half-open probe
half_open_max_calls	Int32	1	Max probe requests in half-open

How It Works

When enabled, the RedisStore wraps operations with the circuit breaker. On failure:

1. Failure count increments

2. When failure_count >= failure_threshold, circuit opens

3. In open state, all requests immediately raise CircuitOpenException (caught as StorageConnectionException)

4. After reset_timeout, circuit transitions to half-open and allows a probe request

5. If the probe succeeds, circuit closes. If it fails, circuit reopens.

Monitoring

breaker = store.circuit_breaker

breaker.state              # => CircuitState::Closed
breaker.failure_count      # => 0
breaker.allow_request?     # => true
breaker.time_until_retry   # => nil (or Time::Span when open)

Manual Reset

store.circuit_breaker.try(&.reset!)

See Also

• Retry Logic

• Error Handling