What Does a Circuit Breaker Do? (from pybreaker)

Let’s say you want to use a circuit breaker on a function that updates a row in the customer database table.

def update_customer(cust):
    # Do stuff here...
    pass

# Will trigger the circuit breaker
updated_customer = await db_breaker.call(update_customer, my_customer)

According to the default parameters, the circuit breaker db_breaker will automatically OPEN the circuit after 5 consecutive failures in update_customer.

When the circuit is OPEN, all calls to update_customer will fail immediately (raising a CircuitBreakerError) without any attempt to execute the real operation.

After 60 seconds, the circuit breaker will allow the next call to update_customer pass through. This state is called HALF OPEN . If that call succeeds, the circuit is CLOSED ; if it fails, however, the circuit is OPEN ed again until another timeout elapses.

Excluding Exceptions(from pybreaker)

By default, a failed call is any call that raises an exception. However, it’s common to raise exceptions to also indicate business exceptions, and those exceptions should be ignored by the circuit breaker as they don’t indicate system errors.

# At creation time...
db_breaker = CircuitBreaker(exclude=[CustomerValidationError])

# ...or later
db_breaker.add_excluded_exception(CustomerValidationError)

In that case, when any function guarded by that circuit breaker raises CustomerValidationError (or any exception derived from CustomerValidationError), that call won’t be considered a system failure.

What does Infuse do?

Infuse, when initializing the Insanic application

1. Sets its own state on the storage as defined in INFUSE_INITIAL_CIRCUIT_STATE.

2. Patches Insanic’s Service object to wrap with circuit breaking.

Other than this, there are some configurations you can tweak. Pretty simple.

For more information, please refer to the Documentation.