Help Center> ROMA Connect> User Guide> Service Integration Guide> Plug-in Management> Circuit Breaker Plug-in
View PDF

Circuit Breaker Plug-in

Overview

ROMA Connect uses circuit breakers to protect the system when performance issues occur on backend services. When the backend service of an API times out for N consecutive times or the latency is long, the circuit breaker downgrade mechanism is triggered to return a error to the API caller or forward the request to the specified backend. After the backend service recovers, the circuit breaker closes and the request becomes normal.

Parameter Description

Table 1 Parameter configuration

Parameter

Description

Trigger Configuration

Circuit Breaker Type

Specify a circuit breaker type.

  • Timeout downgrade: Backend service timeout can trigger a circuit breaker. Once the number of backend service timeouts exceeds the threshold specified within the time window, the circuit breaker is triggered.
  • Condition downgrade: Backend service latency can trigger a circuit breaker. Once the number of timeouts exceeds the threshold specified within the time window, the circuit breaker is triggered.

Conditions

This parameter is mandatory only when Circuit Breaker Type is set to Condition downgrade.

It specifies the latency threshold for the backend service to respond.

Time Window

Configure the time window for circuit breaker triggering. Use this parameter together with Threshold. Once the number of times when conditions are met within the time window exceeds the threshold, the circuit breaker is triggered.

Threshold

Configure the threshold for circuit breaker triggering. Use this parameter together with Time Window. Once the number of times when conditions are met within the time window exceeds the threshold, the circuit breaker is triggered.

NOTE:

A circuit breaker plug-in is triggered by a single gateway component. If ROMA Connect has multiple gateway components, the triggering statistics of each gateway component are collected separately.

For a gateway component, if the maximum times when conditions are met are exceeded within the time window, requests sent to the component trigger the circuit breaker. Other gateway components still forward requests normally.

To view the number of gateway components, go to the Instance Information page of a ROMA Connect instance by clicking the instance name on the console and view the number of IP addresses in Connection Addresses. One IP address indicates one gateway component.

Control Duration

Specify the duration of the circuit breaker. The circuit breaker will be closed at the end of the duration.

Backend Downgrade Policy

Specify whether to enable the backend degradation policy.

  • Enable: The API that triggers the downgrade forwards the request to the specified backend service.
  • Disable: The API does not forward requests to any backend service. It returns an error message indicating that the service is unavailable.

Backend Policy Type

This parameter is mandatory only when Backend Downgrade Policy is enabled.

Set the backend policy type for forwarding requests.

Passthrough: passes the requests to the original API backend service.

Click Add Parameter to add request header parameters to the request forwarded to the backend service.

Downgrade Parameter Settings

Specify whether to enable downgrade configuration. When enabled, it allows you to customize circuit breaker rules that take precedence over other rules.

  • If a custom rule is matched, the downgrade policy configured in the rule is executed. If no trigger condition or downgrade policy is configured in the custom rule, the default trigger condition or downgrade policy is executed.
  • If the custom rule is not matched, the default downgrade policy is executed.

Define Parameters

Define the parameters for rule matching.

  • Parameter: The default value is reqPath, that is, the URI of the API request.
  • Parameter Location: location of the parameter in the API request. The default value is path.

Define Rule

Define the matching conditions, downgrade trigger conditions, and downgrade policies of rules. For details about how to configure trigger conditions and backend service downgrade policies, see the default degradation policy configuration in the preceding description.

Click Add Rule to add rules. The system matches rules from top to bottom. Adjust the rule priority by moving the rules up or down.

  • =: equal
  • !=: not equal to
  • pattern: regular expression
  • enum: enumerated values. Use commas (,) to separate multiple parameter values.

For example, enable Downgrade Parameter Settings and add rules rule01 and rule02 rules in sequence. Disable Trigger Configuration and enable Backend Downgrade Policy for rule01 and enable both parameters for rule02. The circuit breaker first checks whether the matching condition of rule01 is met. If yes, the circuit breaker opens based on the default trigger condition because no trigger condition is configured in rule01, and the backend downgrade policy in rule01 is executed. If no, rule02 is checked.

Script Configuration Example

{
  "breaker_condition": {
    "breaker_type": "timeout",
    "breaker_mode": "counter",
    "unhealthy_threshold": 1,
    "time_window": 1,
    "open_breaker_time": 1
  },
  "downgrade_default": {
    "type": "passthrough",
    "passthrough_infos": [
      {
        "location": "header",
        "name": "sourceip",
        "origin": "SYSTEM",
        "value": "$context.sourceIp"
      },
      {
        "location": "header",
        "name": "header1",
        "origin": "CONSTANT",
        "value": "thisisheader1"
      }
    ]
  },
  "downgrade_parameters": [
    {
      "name": "reqPath",
      "type": "path",
      "value": "path"
    }
  ],
  "downgrade_rules": [
    {
      "rule_name": "rule01",
      "parameters": [
        "reqPath"
      ],
      "match_regex": "[\"reqPath\",\"==\",\"/test123\"]",
      "breaker_condition": {
        "breaker_type": "condition",
        "breaker_mode": "counter",
        "unhealthy_threshold": 0,
        "time_window": 0,
        "open_breaker_time": 0,
        "unhealthy_condition": "[\"$context.backendResponseTime\",\">\",2000]"
      }
      "downgrade_backend": {
        "type": "passthrough",
        "passthrough_infos": [
          {
            "location": "header",
            "name": "downgrade",
            "origin": "CONSTANT",
            "value": "true"
          }
        ]
      }
    }
  ]
}
Parent topic: Plug-in Management