circuitbreaker

Circuit Breaker

The circuit breaker prevents the calling of a service when that service has failed in the past. How the circuit breaker is tripped depends on the mode of operation. There are four modes of operation: contiguous errors, errors within a time period, contiguous errors within a time period, and smart circuit breaker mode.

The available service settings are as follows:

Name	Type	Description
mode	string	The tripping mode: 'a' for contiguous errors, 'b' for errors within a time period, 'c' for contiguous errors within a time period, and 'd' for a probabilistic smart circuit breaker mode. Defaults to mode 'a'
threshold	number	The number of errors required for tripping. Defaults to 5 errors
period	number	Number of seconds in which errors have to occur for the circuit breaker to trip. Applies to modes 'b' and 'c'. Defaults to 60 seconds
timeout	number	Number of seconds that the circuit breaker will remain tripped. Applies to modes 'a', 'b', 'c'. Defaults to 60 seconds

The available input for the request are as follows:

Name	Type	Description
operation	string	An operation to perform: '' for protecting a service, 'counter' for processing errors, and 'reset' for processing non-errors. Defaults to ''

The available response outputs are as follows:

Name	Type	Description
tripped	boolean	The state of the circuit breaker

A sample service definition is:

{
  "name": "CircuitBreaker",
  "description": "Circuit breaker service",
  "ref": "github.com/project-flogo/microgateway/activity/circuitbreaker",
  "settings": {
    "mode": "a"
  }
}

An example series of step that invokes the above CircuitBreaker service:

{
  "service": "CircuitBreaker"
},
{
  "service": "PetStorePets",
  "input": {
    "method": "GET"
  },
  "halt": "($.PetStorePets.error != nil) && !error.isneterror($.PetStorePets.error)"
},
{
  "if": "$.PetStorePets.error != nil",
  "service": "CircuitBreaker",
  "input": {
    "operation": "counter"
  }
},
{
  "if": "$.PetStorePets.error == nil",
  "service": "CircuitBreaker",
  "input": {
    "operation": "reset"
  }
}

Utilizing the response values can be seen in a response handler:

{
  "if": "$.CircuitBreaker.outputs.tripped == true",
  "error": true,
  "output": {
    "code": 403,
    "data": {
      "error": "circuit breaker tripped"
    }
  }
}