pyhystrix

A library to patch requests package in order to add following functionalities by default:

• Connection and Read timeouts
• Retries on connection failure
• Circuitbreaking
• Adding unique x-request-id in request header if not provided

NOTE:: 0.0.2 supports python2.7 and >= 0.0.3 supports python3 only.

Installation

pip3 install pyhystrix

Usage

Before making any request, just call Init():

import requests
import pyhystrix
requests.get("http://abc.xyx") // No functionalities of pyhystrix
pyhystrix.Init()
requests.get("http://abc.xyx") // pyhystrix is attached to all requests

Default Configurations can be changed in 2 ways:

1. Setting following env variables:

   • PHY_CONNECT_TIMEOUT : connection timeout in sec
   • PHY_READ_TIMEOUT: read timeout in seconds
   • PHY_MAX_RETRIES: max number of retries for connection failure
   • PHY_CIRCUIT_FAIL_THRESHOLD: Number of failed requests after which circuit will be open and further requests on the same url will not be allowed.
   • PHY_CIRCUIT_ALIVE_THRESHOLD: Number of failed requests on open circuit to make it half_open (Described below)
   • PHY_CIRCUIT_DELAY: Number of seconds after which open circuit will be half_open.

2. parameters in request itself:

   • max_tries(int): overrides PHY_MAX_RETRIES, some rules related to it are follows:
     • max_tries=0: will cause no retries, fail on first failure.
     • If a positive value is passed for non GET requests, they will be retried too in case received status is in status_forcelist.
   • status_forcelist: list of http status, retry if the returned status is one of these. default is [500] on GET.
   • timeout: same as timeout in requests
   • backoff_factor: delay in each retry will be affected by this using following formula: {backoff factor} * (2 ^ ({number of total retries} - 1)). Default = 0.5sec

More Examples

• GET with retry on multiple failure status codes:

import requests
import pyhystrix
pyhystrix.Init()
request.get("http://abc.xyz", status_forcelist=[501, 502, 403])

• put with retry on response status = 500 or 501

request.put("http://abc.xyz", max_tries=3, status_forcelist=[500, 502])

NOTE: All type of requests will be retried in case of ConnectionError

Circuit Breaker States

1. OPEN : No requests will be allowed
2. HALF_OPEN : Only one request will be allowed
3. CLOSE : All requests will be allowed.

NOTE : State transitions:

CLOSE --> OPEN --> HALF_OPEN --> CLOSE/OPEN

To know more about circuit breaker pattern, click here