https://github.com/valor-software/nest-circuit-breaker

nest-circuit-breaker
https://github.com/valor-software/nest-circuit-breaker

Last synced: 3 months ago
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nest-circuit-breaker

• Host: GitHub
• URL: https://github.com/valor-software/nest-circuit-breaker
• Owner: valor-software
• Created: 2019-06-11T11:51:33.000Z (over 5 years ago)
• Default Branch: development
• Last Pushed: 2020-07-17T06:58:02.000Z (over 4 years ago)
• Last Synced: 2024-03-26T01:02:16.442Z (7 months ago)
• Language: TypeScript
• Size: 17.6 KB
• Stars: 25
• Watchers: 3
• Forks: 2
• Open Issues: 1
• Metadata Files:
  • Readme: README.md

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README

        
# nest-circuitbreaker

This is a wrapper for implementaion of [Circuit Breaker][wiki] pattern(made by [hystrixjs][hystrix]) adapted

for NestJS framework

## Implementation assumptions and constraints

* Every protected method must return a Promise as a result (so async functions and methods are fine 

and this is very convenient with NestJS)

* We can protect only methods of instances that are within NestJS components (annotated with @Component).

This constraint comes from NestJS itself, cause it gives enough control (and possibilities for augmentation)

only over @Components.

* Points above imply that if some of the functionality inside of a @Controller instance needs to be protected

with a Circuit Breaker - this functionality must be extracted in to service (@Component instance).

## Protecting services (@Component instances) with CircuitBreaker

1. Augment service that needs protection.

1. Annotate methods that need protection inside of the service with @CuircuitBreakerProtected annotation

1. Provide an optional configuration for the @CuircuitBreakerProtected annotation

1. Start watching over circuit breaker events (they will be logged)

## Augment service that needs protection

#### Regular component creation

```

@Module({

 modules: [CoreModule],

 controllers: [

   CandidatesController

 ],

 components: [

   CandidatesService

 ]

})

export class NewCandidatesModule {

}

```

#### Circuit Breaker protected component creation

```

@Module({

 modules: [CoreModule],

 controllers: [

   CandidatesController

 ],

 components: [

   {

     provide: CandidatesService,

     useFactory: (logger: Logger, config: Config, api: ApiHelperService) => {

       return addCircuitBreakerSupportTo(new CandidatesService(config, api), CandidatesService);

     },

     inject: [

       Logger, Config, ApiHelperService

     ]

   }

 ]

})

export class NewCandidatesModule {

}

```

## Annotate methods that need protection

#### Annotated service method

```

@Component()

export class CandidatesService {

 // ... 

 @CircuitBreakerProtected({fallbackTo: defaultFallback})

 async searchResumesNode(body: any) {

   return await request({

	// required request options

   });

 }

 // ...

}

```

## @CircuitBreakerProtected annotation configuration

```

// All settings are optional and their default values provided below

@CircuitBreakerProtected({

 circuitBreakerSleepWindowInMilliseconds: 3000,

 circuitBreakerErrorThresholdPercentage: 50,

 circuitBreakerRequestVolumeThreshold: 10,

 timeout: 10000,

 statisticalWindowLength: 10000,

 statisticalWindowNumberOfBuckets: 10,

 percentileWindowLength: 10000,

 percentileWindowNumberOfBuckets: 10,

 requestVolumeRejectionThreshold: 0,

 fallbackTo: undefined,

 shouldErrorBeConsidered: undefined

})

```

## Start watching over circuit breaker events

``` 

export class CoreModule {

 constructor(private logger: Logger,

             private config: Config,

             private sendgridService: SendgridService) {

   const startObservingCircuitBreakerState = makeCircuitBreakerStateObserver(this.sendgridService, logger, config);

   

   // Every 5 seconds (be default) Circuit Breaker will be polled and all opened ones (this is when back off is active)

   //get logged along with health stats

   startObservingCircuitBreakerState();

 }

}

```

## When Circuit Breaker is active (back off is active)

#### This is what gets printed to the console:

```

> "CandidatesService.searchResumesNode" circuit breaker is active.

> Health stats: {totalCount: 100, errorCount: 80, errorsPercentage: 80}

```

[wiki]: https://en.wikipedia.org/wiki/Circuit_breaker_design_pattern

[hystrix]: https://www.npmjs.com/package/hystrixjs