support service worker / pwa's

Start with the config/deploy.js example and trace how the ember-lightning server handles requests for sw.js versus index.html. The work is complete when service-worker content can be deployed and served alongside the application index, with the ref-based preview behavior explicitly resolved or documented.

follow up to conversation with @lukemelia on slack...

so to get the service worker working with the lightning approach here’s what we had to do:

• alias ember-cli-deploy-redis to upload both index and sw.js to parallel nodes: app-name:{index|sw}:current-content

// config/deploy.js
  var moduleName = require('../package.json').name;
  var ENV = {
    pipeline: {
      alias: {
        redis: { as: ['redis-index', 'redis-sw']}
      }
    },
    "redis-index": {
      allowOverwrite: true,
      keyPrefix: `${moduleName}:index`,
      filePattern: 'index.html'
    },
    "redis-sw": {
      allowOverwrite: true,
      keyPrefix: `${moduleName}:sw`,
      filePattern: 'sw.js'
    },
    gzip: {
      // not required but makes troubleshooting a lot easier
      // be sure to add 'content-encoding: gzip' to response if gzip is enabled 
      ignorePattern: 'sw.js'
    },
    // … 
  };

• We then had to update our ember-lightning server to detect requests for sw.js and to respond with the appropriate content where it was always responding with the index.html content previously for any request of a given domain.

• One thing to note is that supporting the ref based preview url isn’t practical here for the service worker itself as we’d need to modify the path embedded in the index file to request this specific version of the service worker. This is certainly possible but isn’t anything that we tackled for now.