Circuit Breakers

In case of an outage, retries can overwhelm the service. To mitigate the issue, we have introduced the concept of circuit breakers in the SDK which can help reduce these ramifications when configured. The SDK is utilizing the CircuitBreaker library to enable this functionality. More information on this library can be found on CircuitBreaker Github page


The basic idea behind the circuit breaker is very simple. A protected function call (a REST call in this case) is wrapped in a circuit breaker object, which monitors for failures. Once the failures reach a certain threshold, the circuit breaker trips, and all further calls to the circuit breaker return with an error, without the protected call being made at all. This saves the service from being overwhelmed with network calls in case of an outage.

Circuit Breaker States

The circuit breaker has a concept similar to the circuit breaker in Electronics. When we reach a overload state, the circuit breaker trips to mitigates the further damage automatically. This behavior is mimicked by the three states of the circuit breaker in the SDK.


This is the initial state of the circuit breaker. In this state, the circuit breaker allows all requests to pass through and hit the service. If the requests return success, then the circuit stays in the closed state, if there are any failures the circuit breaker increments the failure count and any subsequent success resets the failure count. When the failure count reaches the failure threshold, the circuit breaker trips and moves to the Open state.


In this state, none of the network calls are allowed to hit the service for reset timeout duration. After the reset timeout, the circuit transitions into the half open state.

Half Open

In this state, the circuit is ready to make a real call as trial to see if the problem is fixed. If the call results in success, the circuit transitions into the closed state, otherwise, the reset timeout is restarted and the circuit is put back into the open state.

Circuit Breaker Strategy

The CircuitBreakerStrategy is a helper class that users can utilize to configure custom circuit breaker strategy that suits their needs.

Creating a custom CircuitBreakerStrategy

An example on how to create a custom circuit breaker strategy using this helper class is as follows:-

import oci
from oci.circuit_breaker import CircuitBreakerStrategy

# Create a custom Circuit Breaker Strategy.
custom_circuit_breaker_strategy = CircuitBreakerStrategy(
        409: ["IncorrectState", "Conflict"],
        429: [],


The SDK vends a convenient DEFAULT_CIRCUIT_BREAKER_STRATEGY for users to use to enable circuit breakers with ease. The default circuit breaker strategy has the following configuration:-

  • failure_threshold: 10
  • recovery_timeout: 30 seconds
  • failure_statuses_and_codes:
    • HTTP 409/IncorrectState
    • HTTP 429
    • HTTP 500
    • HTTP 502
    • HTTP 503
    • HTTP 504


The DEFAULT_CIRCUIT_BREAKER_STRATEGY should not be modified. Users can use use the GLOBAL_CIRCUIT_BREAKER_STRATEGY instead to modify the circuit breaker behavior at the global level.

Configuring Circuit Breaker

By default, clients exposed in the SDK do not have circuit breakers, but circuit breakers can be enabled/disabled in the SDK at a per client level or for all clients at the global level.

Client level

Each client object accepts a circuit_breaker_strategy keyword argument which can be used to set the circuit breaker strategy for all operations for that client. This circuit breaker strategy could be:

Global level

Users can define a global level circuit breaker strategy programmatically by using oci.circuit_breaker.GLOBAL_CIRCUIT_BREAKER_STRATEGY variable. This strategy will be used by all clients unless overridden by individual clients by using their circuit_breaker_strategy keyword argument. This circuit breaker strategy can take the following values:

The SDK also provides a handy alternative to enable/disable Circuit Breakers with Default Circuit Breaker Strategy at global level by setting the environment variable OCI_SDK_DEFAULT_CIRCUITBREAKER_ENABLED to True/False.


Please note that this environment variable is read only once during SDK initialization.

Circuit Breaker Precedence

The Circuit Breaker Precedence in Python SDK (Highest to lowest) is defined as below:-

  • Client level Circuit Breaker strategy
  • Global level Circuit Breaker strategy set using oci.circuit_breaker.GLOBAL_CIRCUIT_BREAKER_STRATEGY
  • Environment level override to use default Circuit Breaker strategy at global level via the OCI_SDK_DEFAULT_CIRCUITBREAKER_ENABLED environment variable.


Once a client has been configured with a circuit breaker strategy it can not be modified or removed!


Some services have enabled circuit breakers for clients by default which would follow the oci.circuit_breaker.DEFAULT_CIRCUIT_BREAKER_STRATEGY. This can be overridden using any alternatives mentioned above. To know which service clients have circuit breakers enabled, look at the service client’s description in the SDK - it will say either that it has circuit breakers enabled by default, or that it does not have circuit breakers enabled by default


A sample on using circuit breakers, including the default strategy and a custom strategy, can be found on GitHub

Configuring Circuit Breaker CallBack Function

Users using the circuit breakers may be interested in performing some custom actions (like logging, metrics, etc) whenever an API call gets blocked by the circuit breakers. This can be achieved by using the circuit_breaker_callback functionality.

To use this feature you will need to pass a function as an argument to the circuit_breaker_callback parameter while creating a service client. This function takes in one argument of type CircuitBreakerError to get the exception raised by the configured circuit breaker back from the SDK. The definition for CircuitBreakerError can be found here.

An sample code is as follows:-

import oci
import logging

# Simple callback function
def callback_function(circuit_breaker_exception):
    logger = logging.getLogger(__name__)

#  Setting configuration
#  Default path for configuration file is "~/.oci/config"
config = oci.config.from_file()

identity_client = oci.identity.IdentityClient(config,
user = identity_client.get_user(user_id=config['user']).data
print('User data:{}'.format(user))