The Google Container Engine Java Library allows developers to integrate the Google Container Engine API's functions into their Java applications. Developers can add the library to their Maven or Gradle projects using the code provided, or they can download the necessary jars as a zip file.
It appears that Apple may be working on adding service workers support to WebKit. The WebKit Feature Status webpage has recently been changed from "Under Consideration" to "In Development." This change may be an indication that Apple will eventually support Progressive web apps (PWAs).