cluster.md

express-sharp-server

Cluster

It is possible to use the middleware in a clustered enviroment, where a number of express servers are started. express-sharp-server middleware can be used in a clustered enviroment. However, the caching mechanism needs to be prepared for this purpose, because a asynchronous cache creation can leed into race conditions. To deal with this, the caching funtionality must be started in the master as well as in the worker scope.

Server

const cluster = require('cluster');
const express = require('express');
const ImgSrv = require('express-sharp-server');
const CacheMgr = require('express-sharp-server/lib/CacheMgr');

const numCPUs = 4;

if (cluster.isMaster) {
  
  // start the Cache Manager so that clustering is 
  // initialized for caching
  new CacheMgr(cluster);

  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`);
  });
} 
else {
  const server = express();

  server.use(ImgSrv({
    data_dir: '/data/'
  }));

  server.listen(8080);
}