Overview

lua-circuit-breaker provides circuit-breaker functionality like resilience4j i.e. for Java.
Any IO function/method that can fail can be wrapped around lua-circuit-breaker and can be made to fail fast, leading to improved resiliency and fault tolerance.

How does it work?

1. The library creates a CB(circuit breaker) object for a function.
2. Before making the function call, we call CB._before(). This will return an error if the circuit breaker is in open state otherwise will increment the counter of total_requests by 1.
3. After the function call ends, we call CB._after(CB._generation, ok). If ok is true, the success counter is incremented by 1. Otherwise, the failure counter gets incremented by 1.
4. CB object transitions into three states: closed, open, and half-open based on the settings defined by the user.

Installation

luarocks

luarocks install lua-circuit-breaker

source

Clone this repo and run:

luarocks make

Sample Usage

--Import Circuit breaker factory.
local circuit_breaker_lib = require "lua-circuit-breaker.factory"

--Create a new instance of the circuit breaker factory. Always set version = 0. This is used for flushing the circuit breakers when the configuration is changed.
local circuit_breakers = circuit_breaker_lib:new()

-- Get a circuit breaker instance from factory. Returns a new instance only if not already created.
local settings = {
    version = 1,
    window_time = 10,
    min_calls_in_window= 20,
    failure_percent_threshold= 51,
    wait_duration_in_open_state= 15,
    wait_duration_in_half_open_state= 120,
    half_open_max_calls_in_window= 10,
    half_open_min_calls_in_window= 5,
    notify = function(name, state)
        print(string.format("Breaker [ %s ] state changed to [ %s ]", name, state))
    end,
}
local cb, err = circuit_breakers:get_circuit_breaker(
    "io_call_x", -- Name of circuit breaker. This should be unique.
    "io_calls", -- Used to group certain CB objects into one.
    settings,
)

-- Check state of cb. This function returns an error if the state is open or half_open_max_calls_in_window is breached.
local _, err_cb = cb:_before()
if err_cb then
    return false, "Circuit breaker open error"
end
local generation = cb._generation

-- Call IO method for which circuit breaking is required.
local res, err_http = makeIOCall()

-- Update the state of the cb based on successful / failure response.
local ok = res and res.status and res.status < 500
cb:_after(generation, ok) -- generation is used to update the counter in the correct time bucket.

Openresty Sample Usage

There is a sample nginx openresty application (using docker for ease of usage) on ngx_lua_sample

Parameters

Key	Default	Type	Required	Description
name	NA	string	true	Name of circuit breaker, this should be unique
group	"default_group"	string	false	Group to which the CB object will belong
settings.version	NA	number	true	Maintains version of settings object, changing this will create new CB and flush older CB
settings.window_time	10	number	true	Window size in seconds
settings.min_calls_in_window	20	number	true	Minimum number of calls to be present in the window to start calculation
settings.failure_percent_threshold	51	number	true	% of requests that should fail to open the circuit
settings.wait_duration_in_open_state	15	number	true	Duration(sec) to wait before automatically transitioning from open to half-open state
settings.wait_duration_in_half_open_state	120	number	true	Duration(sec) to wait in half-open state before automatically transitioning to closed state
settings.half_open_min_calls_in_window	5	number	true	Minimum number of calls to be present in the half open state to start calculation
settings.half_open_max_calls_in_window	10	number	true	Maximum calls to allow in half open state
settings.half_open_to_open	NA	function	false	Overrides transition from half-open to open state
settings.half_open_to_close	NA	function	false	Overrides transition from half-open to closed state
settings.closed_to_open	NA	function	false	Overrides transtition from closed to open state
settings.notify	NA	function	false	Overrides with a custom logger function

Available Methods

1. new() : create a new circuit breaker factory
2. get_circuit_breaker(name, group, settings) : create a new CB object
3. check_group(group) : check if this group is present
4. remove_breakers_by_group(group) : remove all CB objects in a group
5. remove_circuit_breaker(name, group) : remove a particular CB inside a group. if group is not passed, "default_group" is assumed.

Inspired by

• moonbreaker
• resilience4j