=  NodeJS -> services readmongo_service, dummy_service

== asynchronous event-driven

TIP: As an asynchronous event-driven JavaScript runtime, Node.js is designed to build scalable network applications.

Almost no function in Node.js directly performs I/O, so the process never blocks. Thanks to this, scalable systems is very reasonable to be developed in Node.js.

https://nodejs.org/en/docs/guides/blocking-vs-non-blocking/[Overview of Blocking vs Non-Blocking^]

TIP: *Node.js* is similar in design to, and influenced by, systems like *Ruby's Event Machine* and *Python's Twisted.*

Node.js takes the event model a bit further. It presents an *event loop as a runtime construct* instead of a library.

*In other systems, there is always a blocking call to start the event-loop.*

Typically,

- behavior is defined through callbacks at the beginning of a script,

- and at the end a server is started through a blocking call like *EventMachine::run().*

[NOTE]
====
In Node.js, there is no such start-the-event-loop call.

- *Node.js* simply *enters the event loop after executing the input script.*

- *Node.js exits the event loop* when there are *no more callbacks to perform.*
====

== threads

Node.js being *designed without threads* doesn't mean you can't take advantage of multiple cores in your environment.

Child processes can be spawned by using our *child_process.fork() API,* and are designed to be easy to communicate with.

TIP: Built upon that same interface is the cluster module, which *allows you to share sockets between processes* to enable load balancing over your cores.


== Video = intro


****
TIP: NodeJS in 10 Minutes and Netflix

video::2gQG4cFjahw[youtube]

video::CZ3wIuvmHeM[youtube]
****

netflix

* 6:50 monolithic
* 8:24 minroservices
* 19:00 microservice
* 37:00

https://netflix.github.io[Netflix on Github]