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Infuse is a Python implementation of the Circuit Breaker pattern, described in Michael T. Nygard's book Release It!.

In Nygard's words, "circuit breakers exists to allow one subsystem to fail without destroying the entire system. This is done by wrapping dangerous operations (typically integration points) with a component that can circumvent calls when the system is not healthy".

This basically extends pybreaker with support for Insanic. For full documentation refer to pybreaker. What is different from pybreaker is that it is an asynchronous implementation with asynchronous storage options.

We needed a lot more customizations compared to what the pybreaker was providing. Especially with async storage options. The whole CircuitBreaker implementation needed to be fixed for asyncio support.

Some people might ask why infuse? My basic thought process:

1. Need a name that starts with "in~"
2. "Circuit Breaker" -> Fuse box
3. infuse?

• pybreaker features +
• aioredis backed storage option

• infuse is only Python 3.4+ (support for asyncio)
  • pybreaker is originally : Python 2.7+ (or Python 3.0+)
• redis if using async redis (aioredis)

Run the following command line to download the latest stable version of infuse from PyPI

$ pip install insanic-infuse

Usage of Infuse is different from pybreaker, where everything is done through the Infuse init_app method.

from insanic import Insanic
from infuse import Infuse

app = Insanic("example", version="0.1.0")
Infuse.init_app(app)

But, before we go on some explanation of what a circuit breaker does:

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.

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.

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.

View release history here

For guidance on setting up a development environment and how to make a contribution to Infuse, see the CONTRIBUTING.rst guidelines.

Distributed under the MIT license. See LICENSE for more information.

Thanks to all the people at my prior company that worked with me to make this possible.

• Documentation: https://infuse.readthedocs.io/en/latest/
• Releases: https://pypi.org/project/insanic-infuse/
• Code: https://www.github.com/crazytruth/infuse/
• Issue Tracker: https://www.github.com/crazytruth/infuse/issues
• Insanic Documentation: http://insanic.readthedocs.io/
• Insanic Repository: https://www.github.com/crazytruth/insanic/