Example of how to integrate into a larger system

[vomc]

Hi,

This is more of a question for an example / documentation links. I am testing out various circuit breakers and opossum is currently on my list. It seems to work well in the toy example provided where you have a simple function but I found that it fails in strange ways if you try to integrated it into a larger system.

For example using breaker.fire() on a class method that calls other class methods seems to fail where it eventually complaints that some method is not available... This is strange and I am not sure why it happens and how I would go about integrating this into a larger system.

In my case I have a class method that calls another method which I am trying to wrap into the CircuitBreaker, i.e. breaker.fire(this.api.someOtherMethod). The someOtherMethod calls a method called post in the other class and the error I get now is [Node] ERROR with circuit breaker TypeError: this.post is not a function

Any links to examples would be appreciated! Thanks

[lance]

Hi @vomc - thanks for the report. Any chance you can provide a reproducible example in code? I suspect it is related somehow to how JavaScript deals with this.

[dayvsonsales]

@lance

Same weird behaviour happened with me. I use an dependency injection resolver and make use of classes. I only can use circuit breaker if I define a anonymous function that calls my class method inside it, otherwise it gives an error inside every foreign classes method calls. For example:

const playlistRecommendationService = container.resolve(PlaylistRecommendationService);

const circuitRecommendByCity = new CircuitBreaker(
      playlistRecommendationService.recommendByCity,
      circuitBreakerOptions,
);

const tracks = await circuitRecommendByCity.fire(cityName);

It throws:

TypeError: Cannot read property 'fetchTemperatureInCelsiusByCityName' of undefined
    at Function.<anonymous> (/Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:16:52)
    at step (/Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:45:23)
    at Object.next (/Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:26:53)
    at /Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:20:71
    at new Promise (<anonymous>)
    at __awaiter (/Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:16:12)
    at Function.PlaylistRecommendationService.recommendByCity (/Users/dayvsonsales/microservices-resiliency-typescript/src/modules/playlists/services/PlaylistRecommendationService.ts:63:16)
    at /Users/dayvsonsales/microservices-resiliency-typescript/node_modules/opossum/lib/circuit.js:521:38
    at new Promise (<anonymous>)
    at CircuitBreaker.call (/Users/dayvsonsales/microservices-resiliency-typescript/node_modules/opossum/lib/circuit.js:497:12)

But if I use anonymous function, as the example below, everything works.

const playlistRecommendationService = container.resolve(
      PlaylistRecommendationService,
);

const circuitRecommendByCity = new CircuitBreaker(
      () => playlistRecommendationService.recommendByCity(cityName),
      circuitBreakerOptions,
);

const tracks = await circuitRecommendByCity.fire();

Also, inside the PlaylistRecommendationService I use a lot of this context, maybe there's some problem with it.

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity.

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity.

[lance]

@lholmquist do you think we can identify an actual issue to work on here? If not, maybe this issue can be closed?

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity.

[iamelevich]

@dayvsonsales It's not connected to the library. This is how JS works. So if you want to call it without anonymous function - you should say to function what it should use as this using bind. In your example this should work:

const playlistRecommendationService = container.resolve(PlaylistRecommendationService);

const circuitRecommendByCity = new CircuitBreaker(
      playlistRecommendationService.recommendByCity.bind(playlistRecommendationService),
      circuitBreakerOptions,
);

const tracks = await circuitRecommendByCity.fire(cityName);

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity.