turdus

Turdus

Turdus is a client side HTTP Round-robin and Weighted round-robin load balancing library.

It provides following features:

• Client side Load balancing
• Fault tolerance
• Normalized Response on request failure.
• Mutiple apps supported.

Principle

For simple Round-robin, it is basically array loop.

For weighted round robin algorithm, on each peer selection we increase current_weight of each eligible peer by its weight, select peer with greatest current_weight and reduce its current_weight by total number of weight points distributed among peers.

see also: nginx implementation

[Deprecated] For weighted round robin algorithm (gcd version):

• calculate GCD of all endpoints' weight
• choose the max weighted endpoint then minus GCD
• if largest weight belongs to more than one endpoint, choose the small index one.
• set to original weight until no weight bigger than zero.
• repeat the procedures above.

Usage

install turdus by npm.

npm install turdus

Provide or fetch your callee apps' IP/domain from written configs

or subscribe event by eureka client and fetchRegistry from Eureka

• simple polling each server.

const Turdus = require('turdus');
// initialize multiple app
const trudus = Turdus({ 
  bird: ['127.0.0.1', '127.0.0.2', '127.0.0.3'],
  kitten: ['192.168.0.1', '192.168.0.2', '192.168.0.3'],
});

async function touchServer() {
  await turdus.request('bird', {
    method: 'GET',
    uri: '/cat-books',
  });
}

touchServer();
touchServer();
touchServer();
// ...

// will touch known resources one by one.
//
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.3/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.3/cat-books
// ...

• weighted polling each servers;

const Turdus = require('turdus');
const turdus = Turdus({ bird: [
  { server: '127.0.0.1', weight: 5 },
  { server: '127.0.0.2', weight: 10 },
  { server: '127.0.0.3', weight: 4 },
]});

async function touchServer() {
  await turdus.request('bird', {
    method: 'GET',
    uri: '/cat-books',
  });
}

touchServer();
touchServer();
touchServer();
// ...

// will touch known resources by their weight.
//
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.3/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.3/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.3/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.2/cat-books
// curl http://127.0.0.3/cat-books
// curl http://127.0.0.1/cat-books
// curl http://127.0.0.2/cat-books
// ...

• fault tolerance and nomalize error response.

const turdus = Turdus({ bird: [ '127.0.0.1', '127.0.0.2' ] });
turdus.fakePositiveRes('bird', {
  '/cat-birds': 'though some error appeared',
  '/cat-books': [ 'The Fountainhead', 'Poor Charlie's Almanack:The Wit and Wisdom of Charles T. Munger', 'The Little Prince' ],
});

turdus.request('bird', {
  uri: '/cat-birds',
  method: 'POST',
  body: { yy: 6 },
  json: true,
})
.then((result) => {
  // though enpoints is not touchable
  // we can get positive response due to preset method.
  // result.statusCode: 200
  // result.body: 'though some error appeared',
});

• update exist applications' endpoints or add new applications.

const endpoints = {
  kitten: [
    { server: '127.0.0.1', weight: 0 },
    { server: '127.0.0.2', weight: 0 },
  ],
  doggy: [
    { server: '192.168.0.1', weight: 0 },
    { server: '192.168.0.2', weight: 0 },
  ],
};
const turdus = Turdus(endpoints);
turdus.upsertEndpoints({
  doggy: [
    { server: '192.168.0.1', weight: 3 },
    { server: '192.168.0.2', weight: 3 },
    { server: '192.168.0.3', weight: 1 },
    { server: '192.168.0.4', weight: 1 },
  ],
});

// the doggy application's endpoints will be changed.
// also it's balance type got changed from raw to weighted.

NOTE: this function may reset related applications' current polling order to original status.

License

MIT