profuse

Profuse is an implementation of the "circuit breaker" pattern, using promises instead of callbacks. It's written in typescript so you can use type-safe checks if you want to (but you don't have to).

A "circuit breaker" wraps a remote call (for example, to a database or a REST service), watching for exceptions. If too many exceptions happen, the breaker trips.

Once tripped, all calls will fail immediately. After a while, the breaker will move into probation mode, where a single success will reset it back to normal mode, or a single failure will cause it to trip again. This allows failing remote services to "fail fast" and stops your client from pummeling them while they're down.

Usage

const breaker = new CircuitBreaker("database", { tripRate: 0.95 });
breaker.do(() => {
  return db.getUser(userId);
}).then(user => ... );

The options are documented in profuse.ts.

There is also a callback version, if you aren't comfortable with promises yet, or are targeting older platforms. The syntax is a bit more confusing because of the inside-out nature of callbacks: It accepts a function that takes a callback, and your callback.

const breaker = new CircuitBreaker("database", { tripRate: 0.95 });
breaker.doCallback(cb => fs.open(path, flags, cb), (error, file) => {
  // do things with file
});

If you prefer, you can use the lower-level API:

const breaker = new CircuitBreaker("database", { tripRate: 0.95 });
breaker.tryStart();  // throws an exception if the circuit breaker has tripped
fs.open(path, flags, (error, file) => {
  breaker.registerResult(error == null);
  // do things with file
});

Logic

In normal mode, trip if:

• less than X percent (tripRate) of the last N requests (window) succeeded
• too many (maxConcurrent) concurrent requests (may indicate a too-long or missing timeout)

In tripped mode, go into probation if:

• time has passed (checkInterval)

In probation mode:

• any successful request: go back to normal mode
• any failed request: go back to tripped mode

Build

$ npm i
$ npm test

License

Apache 2 (open-source) license, included in LICENSE.txt.

Authors

@robey - Robey Pointer [e-mail]