Sharding and Load Balancing in Scala - Twitter's Finagle
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The document discusses sharding and load balancing in Scala using Twitter's Finagle, an extensible and protocol-agnostic RPC system built on Netty. It includes code examples demonstrating the setup of workers and sharding service, along with thoughts on the documentation and API exposure. The author shares reflections on the technology's expressiveness and challenges faced in its implementation.
![object Worker extends App {
try {
// Collect args
val port = Integer.parseInt(args(0))
val value = args(1)
// Define our service - just return the value provided!
val service = new Service[HttpRequest, HttpResponse] {
def apply(req: HttpRequest) = {
val buffer = ChannelBuffers.copiedBuffer(value, Charset.forName("UTF-8"))
val response = new DefaultHttpResponse(req.getProtocolVersion, HttpResponseStatus.OK)
response.setHeader(HttpHeaders.Names.CONTENT_TYPE, "text/plain")
response.setHeader(HttpHeaders.Names.CONTENT_LENGTH, buffer.readableBytes())
response.setContent(buffer)
Future.value(response)
}
}
>>> Worker (1)](https://image.slidesharecdn.com/finagle-130823021324-phpapp01/85/Sharding-and-Load-Balancing-in-Scala-Twitter-s-Finagle-5-320.jpg)
![// Define our service - scatter to the shards and gather the results
val service = new Service[HttpRequest, HttpResponse] {
def apply(req: HttpRequest) = {
Future.collect(shards.map(shard => { // Scatter
shard(req).map(resp => resp.getContent().toString(CHARSET))
}))
.map(resps => { // Gather
val bf = ChannelBuffers.copiedBuffer(resps.reduceLeft(_+":"+_), CHARSET)
val resp = new DefaultHttpResponse(req.getProtocolVersion, HttpResponseStatus.OK)
resp.setHeader(HttpHeaders.Names.CONTENT_TYPE, "text/plain")
resp.setHeader(HttpHeaders.Names.CONTENT_LENGTH, bf.readableBytes())
resp.setContent(bf)
resp
})
}
}
>>> Sharder (service)](https://image.slidesharecdn.com/finagle-130823021324-phpapp01/85/Sharding-and-Load-Balancing-in-Scala-Twitter-s-Finagle-8-320.jpg)
Sharding and Load Balancing in Scala - Twitter's Finagle
- 1. Sharding and Load Balancing in Scala Twitter's Finagle Geoff Ballinger Technical Advisor at Mobile Acuity Ltd.
- 2. • some ML and Lisp in the early 90s • C, C++ and Java since – embedded and server • apps on BB, Android and iOS • Mobile • Startups • Scaling • Integration • Deployment & Ops >>> Background
- 3. >>> Finagle https://blog.twitter.com/2011/finagl e-protocol-agnostic-rpc-system • Finagle is an extensible RPC system for Scala • Protocol-agnostic and asynchronous • Created, used and published by Twitter • Built on netty and thus NIO • Heavy use of Futures etc • http://twitter.github.io/finagle/
- 4. • Multiple HTTP workers – part of the result • Each shard is one or more identical workers • Sharder scatters requests to the shards and gathers the results • Load balance between workers • Fault tolerant • Chance to play w/ Scala in anger! • (Simple rational reconstruction) >>> A simple sharder?
- 5. object Worker extends App { try { // Collect args val port = Integer.parseInt(args(0)) val value = args(1) // Define our service - just return the value provided! val service = new Service[HttpRequest, HttpResponse] { def apply(req: HttpRequest) = { val buffer = ChannelBuffers.copiedBuffer(value, Charset.forName("UTF-8")) val response = new DefaultHttpResponse(req.getProtocolVersion, HttpResponseStatus.OK) response.setHeader(HttpHeaders.Names.CONTENT_TYPE, "text/plain") response.setHeader(HttpHeaders.Names.CONTENT_LENGTH, buffer.readableBytes()) response.setContent(buffer) Future.value(response) } } >>> Worker (1)
- 6. // Run this worker over the required port val server = ServerBuilder() .codec(Http()) .bindTo(new InetSocketAddress(port)) .name("Shard") .build(service) } catch { case t: Throwable => { System.err.println(t.getMessage()) System.err.println("Usage: Worker <port> <value>") } } } >>> Worker (2)
- 7. // Collect port arg val port = Integer.parseInt(args(0)) // Build up shards from host specs on remaining command line val shards = args.tail.map(spec => { ClientBuilder() .codec(Http()) .hosts(spec) .hostConnectionLimit(10) .retryPolicy(policy) .build() }) >>> Sharder (setup)
- 8. // Define our service - scatter to the shards and gather the results val service = new Service[HttpRequest, HttpResponse] { def apply(req: HttpRequest) = { Future.collect(shards.map(shard => { // Scatter shard(req).map(resp => resp.getContent().toString(CHARSET)) })) .map(resps => { // Gather val bf = ChannelBuffers.copiedBuffer(resps.reduceLeft(_+":"+_), CHARSET) val resp = new DefaultHttpResponse(req.getProtocolVersion, HttpResponseStatus.OK) resp.setHeader(HttpHeaders.Names.CONTENT_TYPE, "text/plain") resp.setHeader(HttpHeaders.Names.CONTENT_LENGTH, bf.readableBytes()) resp.setContent(bf) resp }) } } >>> Sharder (service)
- 10. >>> Reflections and Opinions • Concise and expressive • Shoulders of giants • Poorly documented • Exposes too many lower APIs • Twitter vs Scala vs Akka Futures!