resilient.js

A browser and node.js fault tolerant, dynamic servers auto discovery, balanced, configurable and full featured HTTP client for distributed and reactive system architectures

For more information about Resilient, see the project site and the request flow algorithm

Note: resilient.js is still beta

Features

• Fault tolerant, transparent server fallback
• Client-side based balancer using a simple best availability algorithm
• Smart balancer logic based on server score (network latency, errors and succesfull requests)
• Discern servers availability score calculus per read and write operations when balancing
• Configurable balancer policy by weight
• Built-in support for in/out traffic interceptors
• Built-in support for servers caching to improve reliability in fallback
• Highly configurable (timeout, retry loop, cache, wait delay fallback...)
• Parallel servers discovering for a faster availability
• Cross engine (node.js and browsers. ES5 compliant)
• Configurable alternative HTTP client to use as forward proxy (instead of using the embeded one)
• Dynamic servers discovery (based on the resilient specification protocol)
• Support mock/stub operation mode
• Full HTTP features support (it uses internally request and lil-http for the browser)
• Server-side dynamic client configuration support (experimental)
• Support round robin scheduling algorithm for traffic distribution (experimental)
• Lightweight library (7KB gzipped)

Installation

Node.js

npm install resilient

Browser

Via Bower

bower install resilient

Via Component

component install resilient-http/resilient.js

Or loading the script remotely

<script src="//cdn.rawgit.com/resilient-http/resilient.js/0.1.11/resilient.js"></script>

Environments

It runs properly in any ES5 compliant engine

• Node.js
• Chrome >= 5
• Firefox >= 3
• Safari >= 5
• Opera >= 10
• IE >= 9

How it works?

An algorithm diagram worth more than words

Basic usage

If require is available, you must use it to fetch the module. Otherwise it will be available as global exposed as resilient

var Resilient = require('resilient')

Static servers

Define your servers pool

var servers = [
  'http://api1.server.com',
  'http://api2.server.com',
  'http://api3.server.com'
]

Create a new client and set the servers to balance

var client = Resilient({ service: { basePath: '/api/1.0' }})
client.setServers(servers)

Perform the request (the best available server will be used automatically)

client.get('/users', function (err, res) {
  if (res.status === 200) {
    console.log('Success:', res.data)
  }
})

Dynamic servers discovery

Define the discovery servers pool

var servers = [
  'http://discover1.server.com',
  'http://discover2.server.com',
  'http://discover3.server.com'
]

Create a new client and set the discovering servers

var client = Resilient({ service: { basePath: '/api/1.0' }})
client.discoveryServers(servers)

Perform the request (and that's all, forget about anything else)

client.get('/users', function (err, res) {
  if (res.status === 200) {
    console.log('Success:', res.data)
  }
})

API

resilient([ options ])

Creates a new resilient client with custom config

Options

The options object has three different first-level properties of configuration

Resilient({
  service: { ... }
  discovery: { ... }
  balancer: { ... }
})

Service

There are specific config options for the servers of the client service. Resilient is a resource-oriented HTTP client, which could be ideal for RESTful Web services

• servers array - A list of valid URIs of servers to reach for the given service. Default null. It's recommended you use discovery servers instead
• retry number - Number of times to retry if all requests failed. Use Infinity for infinitive attemps. Default 0
• retryWait number - Number of milisenconds to wait before retry attempt cycle. Default to 1000
• discoverBeforeRetry boolean - Force to refresh service servers list from asking for discovery servers on each retry attempt. You must define the discovery servers in order to use this feature. Default true
• promiscuousErrors boolean - Enable promiscuous error handling mode. Client HTTP status errors (400-499) will be treated as failed requests and Resilient will treat it as unavailable error response, retrying the request until it has valid status (if retry option was configured). Default false
• refresh number - Server refresh interval time in miliseconds

Specific shared configuration options for the HTTP client for final service requests

• path string - Server request path as part of the final URL
• basePath string - Server resource base path to share between all requests
• method string - Request HTTP method. Default to GET
• data mixed - Payload data to send as body request
• headers object - Map of strings representing HTTP headers to send to the server
• params object - Map of strings representing the query params
• timeout number - Request maximum timeout in miliseconds before to abort it. Default to 10 seconds
• auth object - Authentication credentials to the server. Object must have both user and password properties

Browser specific options

• async boolean - Set to false if the request must be performed as synchronous operation (not recommended, browser only)
• withCredentials boolean - Whether to set the withCredentials flag on the XHR object. See [MDN][withcredentials] for more information
• responseType string - Define how to handle the response data. Allowed values are: text, arraybuffer, blob or document

Node.js specific options

See all HTTP options supported for node.js here

Balancer

• enable boolean - Enable/disable the smart client balancer. Default true
• roundRobin boolean - Enable RobinRobin scheudle algorithm (experimental)
• roundRobinSize number - Round robin round size. Useful to increase requests distribution across different servers. Default to 3 servers
• weight object - Balacer point percentage weight for server scoring policy:
  • success number - Percentage weight for success request. Default to 15
  • error number - Percentage weight for failed request. Default to 50
  • latency number - Percentage weight for request average latency. Default to 35

Discovery

Specific configuration for discovery servers requests, behavior and logic

• servers array - A list of valid URIs of endpoints to use as discovery servers
• cache boolean - Enable/disable discovery servers cache in case of global fallback. Default true
• cacheExpiration number - Maximum cache time to live. Default to 10 minutes
• retry number - Number of times to retry if all requests failed. Use Infinity for infinitive attemps. Default 3
• retryWait number - Number of milisenconds to wait before retry attempt cycle. Default to 1000
• parallel boolean - Discover servers in parallel. Improve service availability and decrement delay times. Recommended. Default true
• refresh number - Servers list refresh interval in miliseconds. Default to 60000
• promiscuousErrors boolean - Enable promiscuous error handling mode. Client HTTP status errors (400-499) will be treated as failed requests and Resilient will treat it as unavailable error response, retrying the request until it has valid status (if retry option was configured). Default false

Specific shared configuration options for the HTTP client for discovering processes

• path string - Server request path as part of the final URL
• basePath string - Server resource base path to share between all requests
• timeout number - Server discovery network timeout in miliseconds. Default 2 seconds
• auth object - Authentication credentials required for the discovery server. Object must have both user and password properties
• params object - Map of strings representing the query params
• headers object - Map of strings representing HTTP headers to send to the discovery server
• method string - Request HTTP method. Default to GET
• data mixed - Optional data to send as payload to discovery servers. Default null

For node.js, see all HTTP options supported here

Request callback arguments

• error Error|ResilientError - Response error, if happends. Otherwise null
• response Object|http.IncomingMessage - Response object

Response

Browser

• data mixed - Body response. If the MIME type is JSON-compatible, it will be transparently parsed
• status number - HTTP response status code
• headers object - Response headers
• xhr object - Original XHR instance
• error mixed - Error info, usually an Error instance (in case that an error happens)

Node.js

See http.IncomingMessage

Error

It will be an Error instance with the following members

• message string - Human readable error message
• status number - Internal error code or HTTP status
• code number - Optional error code (node.js only)
• stack string - Optional stack error trace
• request object - Original response object (node.js only). Optional
• error Error - Original throwed error object (node.js only). Optional
• xhr XMLHttpRequest - XHR native instance (browser only)

Built-in error codes

• 1000 - All requests failed. No servers available
• 1001 - Cannot update discovery servers. Empty or invalid response body
• 1002 - Missing discovery servers. Cannot resolve the server
• 1003 - Cannot resolve servers. Missing data
• 1004 - Discovery server response is invalid or empty
• 1005 - Missing servers during retry process
• 1006 - Internal state error (usually caused by an unexpected exception)

Events

Resilient client has a built-in support for internal states event dispacher and notifier to the public interface

This could be useful really useful while using an interceptor pattern in order to detect states and data changes. You can intercept and change any request configuration and response subscribing to the pre/post hooks. Note that mutation is required, you should modify it by reference and do not lose it

discovery.refresh

Arguments: servers<Array>, resilient<Resilient>

Fired every time that servers are updated from discovery servers

discovery.cache

Arguments: servers<Array>, resilient<Resilient>

Fired every time that servers cache is updated

request.start

Arguments: options<Object>, resilient<Resilient>

Fired as before a request is created

You can intercept and modify the request options on the fly, but you must mutate the options object and do not lose its reference

request.finish

Arguments: error<Error>, response<Object|http.IncomingMessage>, resilient<Resilient>

Fired as after a request was completed

You can intercept and modify the error/response on the fly, but you must mutate the options object and do not lose its reference

resilient#send(path, options, callback)

Performs a custom request with the given options. It's recommended using as generic interface to make multi verb requests

resilient#get(path, options, callback)

Creates a GET request with optional custom options

resilient#post(path, options, callback)

Creates a POST request with optional custom options

resilient#put(path, options, callback)

Creates a PUT request with optional custom options

resilient#del(path, options, callback)

Creates a DELETE request with optional custom options

resilient#patch(path, options, callback)

Creates a PATCH request with optional custom options

resilient#head(path, options, callback)

Creates a HEAD request with optional custom options

resilient#setOptions(options)

Define custom options. See supported options

resilient#getOptions()

Return: Options

Retrieve the current options

resilient#setServiceOptions(options)

Define custom service-level options

resilient#setDiscoveryOptions(options)

Define custom service-level options

resilient#getHttpOptions(type)

Return: object

Get a map of HTTP specific options

resilient#servers([ type = 'service' ])

Return: Servers

Return a the current servers list. Allowed types are: service and discovery

resilient#discoveryServers([ servers ])

Return: Servers

Setter/Getter for discovery servers list

resilient#discoverServers([ options, ] cb)

Return: Resilient

Pass to the callback an up-to-date list of servers asking to discovery servers

resilient#getUpdatedServers([ options, ] cb)

Return: Resilient Alias: getLatestServers

Pass to the callback an up-to-date list of servers, with or without discovery servers configured

resilient#updateServers([ options, callback ])

Force to update the servers list from discovery servers, if they are defined, optionally passing a callback to handle the result

resilient#setHttpClient(fn)

Use a custom HTTP client as proxy instead of the embedded resilient native HTTP client.

Useful to define use proxy for custom frameworks or libraries in your existent project when you need to deal with some complex HTTP pre/post hooks logic and exploit custom HTTP client features

If defined, all the outgoing requests through Resilient client will be proxied to it.

Arguments passed to the client function:

• options object - Resilient HTTP service options
• callback function - Request status handler. Expected arguments are: error, response

Note: error and response objects must be compatible with the current interface

resilient#restoreHttpClient()

Restore the native resilient HTTP client

resilient#mock(mockFn)

Define a mock/fake HTTP client error/response object for all outgoing requests

resilient.mock(function (options, cb) {
  if (options.url === 'http://discovery.server.me') {
    // fake response
    cb(null, { status: 200, data: ['http://server.net'] })
  } else {
    // fake unavailable status
    cb(null, { status: 503 })
  }
})

See also the setHttpClient() method for custom request proxy forward, also useful for testing with stubs/fakes

resilient#unmock()

Disable the mock/fake mode

resilient#on(event, handler)

Subscribe to an event. See supported events

resilient#off(event, handler)

Unsubscribe a given event and its handler. See supported events

resilient#once(event, handler)

Subscribe to an event with a given handler just once time. After fired, the handler will be removed

See supported events

resilient#flushCache()

Force to flush servers cache

resilient#client()

Return: Client

Returns an HTTP client-only interface. Useful to provide encapsulation from public usage and avoid resilient-specific configuration methods to be called from the public API. This is a restricted API useful to provide for high-level developers

resilient#areServersUpdated()

Return: boolean

Returns true if servers are up-to-date. Otherwise false

resilient#balancer([ options ])

Return: object

Returns the current balancer config options

resilient.VERSION

Type: string

Current semver library version

resilient.CLIENT_VERSION

Type: string

Current semver HTTP client library version

resilient.defaults

Type: object

Default config options

resilient.Servers(list)

Create a new servers store

resilient.Options(options)

Create a new options store

resilient.Client(resilient)

Creates a new resilient HTTP client with public API

Useful to provide encapsulation to the resilient API and expose only the HTTP client (the common interface the developers want to consum)

resilient.request(options [, cb])

Use the plain HTTP client

Contributing

Wanna help? Cool! It will be appreciated :)

You must add new test cases for any new feature or refactor you do, always following the same design/code patterns that already exist

Development

Only node.js is required for development

Clone the repository

$ git clone https://github.com/resilient-http/resilient.js.git && cd resilient.js

Install development dependencies

$ npm install

Install browser dependencies

$ bower install

Generate browser bundle source

$ make browser

Run tests (in a headless browser)

$ make test

License

MIT © Tomas Aparicio and contributors