Service Configurations

Load Balancing Policy

The content of this page has been outdated, please refer to Load Balancing

Rate Limiting Policy

Scenario

Users at the provider end can use the rate limiting policy to limit the maximum number of requests sent from a specified microservice per second.

Precautions

There may be a small different between the rate limit and actual traffic.
The rate limit function at the provider end is for service rather than security purpose. To prevent distributed denial of service(DDos) attacks, you need to take other measures.
Traffic control is a microservice-level rather than process-level function.

Configuration

　　Rate limiting policies are configured in the microservice.yaml file. For related configuration items, see Table 2. To enable the rate limiting policy at the provider end, you also need to configure the rate limiting handler on the server in the processing chain and add dependencies in the pom.xml file.

　　An example of microservice.yaml file configuration is as follows,

servicecomb:
  handler:
    chain:
      Provider:
        default: qps-flowcontrol-provider

　　Add dependencies of handler-flowcontrol-qps in the pom.xml file,

<dependency>
    <groupId>org.apache.servicecomb</groupId>
    <artifactId>handler-flowcontrol-qps</artifactId>
    <version>1.0.0-m1</version>
</dependency>

　　Table2 Configuration items of the QPS rate limit

Configuration Item	Default Value	Value Range	Mandatory	Description	Remarks
servicecomb.flowcontrol.Provider.qps.enabled	true	true/false	No	Specifies whether to enable traffic control at the provider end.	-
servicecomb.flowcontrol.Provider.qps.limit.[ServiceName]	2147483647（max int）	(0,2147483647]，Integer	No	Specifies the number of requests allowed per second.	This parameter can only be configured for microservice
servicecomb.flowcontrol.Provider.qps.global.limit	2147483647（max int）	(0,2147483647]，Integer	No	Specifies the total number of requests allowed per second at the provider end	If no configuration is set for any specific microservices, this parameter takes effect

Fallback Policy

Concept Description

A fallback policy is used when a service request is abnormal.

There are three key concepts in fallback: isolation, fallbreak, and fault tolerance:

Isolation is an exception detection mechanism. Two common items that need to be detected are timeout duration and the number of concurrent requests.
Fallbreak is an exception response mechanism, and it depends on isolation. Fallbreak is triggered based on the error rate. Two common items need to set are the number of requests to collect and error rate.
Fault tolerance is an exception handling mechanism that depends on fallbreak. Fault tolerance is called after a fallbreak. For fault tolerance, you need to set the number of fault tolerance call items.

During fallback, if M(the threshold) errors are detected in N requests, the consumer will no longer send requests and the fault tolerance mechanism will be enabled. The preceding fallback process is accepted in Netflix Hystrix and helps you configure the parameters. Obtain information about the parameter configuration at https://github.com/Netflix/Hystrix/wiki/Configuration. Currently, ServiceComb provides two types of fault tolerance modes: returning null values and throwing exceptions.

Scenario

By configuring a fallback policy, you can handler microservice exceptions.

Configuration

　　Configuration items of fallback policies are as follows:

　　Table 3 Configuration items of the fallback policy

Configuration Item	Default value	Value Range	Mandatory	Description	Remarks
servicecomb.isolation.timeout.enabled	FALSE	-	No	Specifies whether to enable timeout detection.
servicecomb.isolation.timeoutInMilliseconds	30000	-	No	Specifies the timeout duration threshold.
servicecomb.isolation.maxConcurrentRequests	10	-	No	Specifies the maximum number of concurrent requests.
servicecomb.circuitBreaker.enabled	TRUE	-	No	Specifies whether to enable fallbreak.
servicecomb.circuitBreaker.forceOpen	FALSE	-	No	Specifies that fallbreak is enable regardless of the number of failed requests or the error rate.
servicecomb.circuitBreaker.forceClosed	FALSE	-	No	Specifies that fallbreak can be implemented at any time.	If this parameter and servicecomb.circuitBreaker.forceOpen both need to be configured, servicecomb.circuitBreaker.forceOpen has priority.
servicecomb.circuitBreaker.sleepWindowInMilliseconds	15000	-	No	Specifies the duration needed to recover from fallbreak.	After the recovery, the number of failed requests will be recalculated. Note: If the consumer fails to send a request to the provider after the recovery, fallbreak is enabled again.
servicecomb.circuitBreaker.requestVolumeThreshold	20	-	No	Specifies the threshold of failed requests sent within 10 seconds. If the threshold is reached, fallbreak is triggered.	Ten seconds will be divided into ten 1 seconds, and the error rate is calculated 1 second later after an error occurred. Therefore, fallbreak can be implemented at least 1 second after the call.
servicecomb.circuitBreaker.errorThresholdPercentage	50	-	No	Specifies the threshold of error rate. If the threshold is reached, fallbreak is triggered.
servicecomb.fallback.enabled	TRUE	-	No	Specifies whether to enable troubleshooting measures after an error occurred.
servicecomb.fallback.maxConcurrentRequests	10	-	No	Specifies the number of fault tolerance(servicecomb.fallbackpolicy.policy) requests concurrently called. If the value exceeds 10, the measures will no longer be called, and exception are returned.
servicecomb.fallbackpolicy.policy	throwexception	returnnulll \| throwexception	No	Specifies the error handling policies after an error occurred.

Caution: Be cautious when setting servicecomb.isolation.timeout.enabled to TRUE, All processes are asynchronously processed in the system, and any error value returned by an intermediate process because the set timeout duration is reached can cause failure of the follow-up processes. Therefore, you are advised to keep the default value FALSE for servicecomb.isolation.timeout.enabled. For timeout duration from the network aspect, you are advised to set servicecomb.request.timeout=30000.

Sample Code

servicecomb:
  handler:
    chain:
      Consumer:
        default: bizkeeper-consumer
  isolation:
    Consumer:
      timeout:
        enabled: true
      timeoutInMilliseconds: 30000
  circuitBreaker:
    Consumer:
      sleepWindowInMilliseconds: 15000
      requestVolumeThreshold: 20
  fallback:
    Consumer:
      enabled: true
  fallbackpolicy:
    Consumer:
      policy: throwexception

NOTE:

You need to enable service governance for fallback, The provider handler is bizkeeper-provider, and the consumer handler is bizkeeper-consumer. If Consumer:/Provider: was omitted, your configuration would not work, and service governance would be enabled with default configuration.