Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
Have Your Node.js Cake
and Eat It Too
Rob Tweed
M/Gateway Developments Ltd
Twitter: @rtweed
http://www.mgateway.com

Copyright © 2014 M/Gateway Developments Ltd

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• Just another Node.js framework?
• What's wrong with the ones already
available and used by thousands of
developers?
– Express.js
– Koa
– Meteor
– Hapi
– Sails, etc etc

Copyright © 2014 M/Gateway Developments Ltd
Two reasons
• Achieving the best interface to Cache &
GT.M from JavaScript
– JavaScript as a first-class language and direct
alternative to Cache ObjectScript / Mumps
– Integrating with legacy Cache ObjectScript /
Mumps code that was inherently synchronous

Copyright © 2014 M/Gateway Developments Ltd
Two reasons
• Achieving the best interface to Cache &
GT.M from JavaScript
– JavaScript as a first-class language and direct
alternative to Cache ObjectScript / Mumps
– Integrating with legacy Cache ObjectScript /
Mumps code that was inherently synchronous
– I've been working with Node.js &
Cache/Mumps since 2011 and have tried
everything you can imagine to figure this out!

Copyright © 2014 M/Gateway Developments Ltd
Two reasons
• Achieving the best interface to Cache &
GT.M from JavaScript
– JavaScript as a first-class language and direct
alternative to Cache ObjectScript / Mumps
– Integrating with legacy Cache ObjectScript /
Mumps code that was inherently synchronous
• Addressing some of the deficiencies in
Node.js that are a direct consequence of
its architecture

Copyright © 2014 M/Gateway Developments Ltd
Node.js Architecture
• Everything executes in a single process
– You might have 1000's of users doing stuff
concurrently
• They're all sharing the same process!

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By Design
• Ryan Dahl, the inventor of Node.js,
wanted to create a highly-scalable, high-
performance architecture for network
programs
– Web servers
– Chat servers
• Showed that the threaded architecture of
Apache had performance limits and heavy
memory usage

Copyright © 2014 M/Gateway Developments Ltd
Node.js Architecture
• Everything executes in a single process
• Non-blocking I/O
– No user activity must block the process, or everyone
grinds to a halt
• Event-driven, asynchronous logic
– Fire off the request, but don't wait for the results
• Carry on with the next task
– When results come back, handle them at the next
opportunity

Copyright © 2014 M/Gateway Developments Ltd
Node.js = server-side JavaScript
• Ryan Dahl wasn't actually a big JavaScript fan
• However, he realised that it was a convenient
language for such an environment, as it's
designed for exactly the same kind of way of
working in the browser
• Google's V8 JavaScript engine was Open
Sourced, so he used it to provide the language
for Node.js
– (which is actually mostly written in C++)

Copyright © 2014 M/Gateway Developments Ltd
Asynchronous Syntax in Other Languages?
• Node.js isn't unique in supporting
asynchronous logic and non-blocking I/O
• Available also in most other modern
languages
– Java
– Python, etc
• Allows efficient use of resources when
making parallel requests for resources
– Files, external web services etc

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Asynchronous Syntax in Node.js
• Node.js is unique in that you have no
option but to use Asynchronous logic

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Node.js Popularity
• Launched in 2009
• Now hugely popular and continuing to
grow in popularity
– Server-side of web / mobile applications
• One reason is that just one language –
JavaScript – is needed for all parts of an
application
– Single skill-set

Copyright © 2014 M/Gateway Developments Ltd
Drawbacks of Node.js
• Even its greatest exponents will tell you
not to use Node.js for certain things
• In every other language, zealots will
encourage you to use it for everything!

Copyright © 2014 M/Gateway Developments Ltd
Drawbacks of Node.js
• Even its greatest exponents will tell you
not to use Node.js for certain things
– CPU-intensive logic
– Complex database manipulation
• Particularly relational database handling

Copyright © 2014 M/Gateway Developments Ltd
Drawbacks of Node.js
• Even its greatest exponents will tell you
not to use Node.js for certain things
– CPU-intensive logic
• Tie up the CPU and everyone else using the
process will be blocked
– Complex database manipulation
• Particularly relational database handling

Copyright © 2014 M/Gateway Developments Ltd
Drawbacks of Node.js
• Even its greatest exponents will tell you
not to use Node.js for certain things
– CPU-intensive logic
– Complex database manipulation
• Particularly relational database handling
– Due to the limitations of asynchronous logic, eg you can't
chain functions

Copyright © 2014 M/Gateway Developments Ltd
Usual Solutions
• Use a third-party queue to offload CPU-
intensive work to some other environment
– RabbitMQ
– ZeroMQ
• Use another language such as Rails for
database-intensive work

Copyright © 2014 M/Gateway Developments Ltd
The down-sides
• Heterogeneous environment
• Multiple skill-sets
• Multiple moving parts
Node.js
RabbitMQ
Rails
Java
Database

Copyright © 2014 M/Gateway Developments Ltd
The down-sides
• Heterogeneous environment
• Multiple skill-sets
• Multiple moving parts
Node.js
RabbitMQ
Rails
Java
DatabaseReminds you of EHMP?

Copyright © 2014 M/Gateway Developments Ltd
Cache/Mumps integration
• Ideally using synchronous logic
– Especially if you have to elegantly and easily
handle locking in legacy code
• Ideally abstract Cache/Mumps databases
in a way that makes intuitive sense to a
JavaScript developer
• Asynchronous logic for complex database
manipulation is painful, time-consuming
and difficult to understand/maintain

Copyright © 2014 M/Gateway Developments Ltd
Async is the New Sync?
• The Node.js community are well aware of
the need to avoid "callback hell" caused
by asychronous logic
• Next version of Node.js will support
Async/Await which greatly improves the
syntax
– Very like synchronous logic

Copyright © 2014 M/Gateway Developments Ltd
Async/Await Doesn't solve:
• Node.js concurrency
– Still need to avoid CPU-intensive code
• High-level database abstractions
– Proper chaining of functions requires
synchronous logic

Copyright © 2014 M/Gateway Developments Ltd
I want my Node.js Cake & Eat it
• I like JavaScript
• I want just one language for everything
– 1 skill set
– 1 set of moving parts
• No extra technologies, thank you
– Keep it simple

Copyright © 2014 M/Gateway Developments Ltd
The Problem is Concurrency
• All concurrent users in Node.js share the
same process

Copyright © 2014 M/Gateway Developments Ltd
The Problem is Concurrency
• All concurrent users in Node.js share the
same process
• As it happens, Amazon Web Services
accidentally created a solution
– And nobody (including AWS) seems to have
realised the consequences of what they've
done

Copyright © 2014 M/Gateway Developments Ltd
AWS Lambda
• "Function As A Service"
• AKA "Serverless"

Copyright © 2014 M/Gateway Developments Ltd
AWS Lambda
• "Function As A Service"
• AKA "Serverless"
• You upload functions
• AWS will execute them
– You don't worry about how or on what physical
machine(s)
• You pay per invocation of your function(s)

Copyright © 2014 M/Gateway Developments Ltd
AWS Lambda
• The first technology they supported was
Node.js

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AWS Concurrency?
• Your function will be invoked in a private
computation container of some sort
• Your function has that container all to itself
for the duration of its execution
• No competition with other concurrent
users

Copyright © 2014 M/Gateway Developments Ltd
Lambda Node.js Examples
• Examples show use of asynchronous APIs
• Node.js users of Lambda use
asynchronous APIs
• They're even excited about the possibility
of using Async/Await in Lambda

Copyright © 2014 M/Gateway Developments Ltd
Lambda Node.js Examples
• Examples show use of asynchronous APIs
• Node.js users of Lambda use
asynchronous APIs
• They're even excited about the possibility
of using Async/Await in Lambda
• But unless your Lambda function really
needs to be asynchronous, why use
asynchronous logic?

Copyright © 2014 M/Gateway Developments Ltd
Asynchronous Syntax in Other Languages?
• Available also in most other modern languages
– Java
– Python, etc
• Allows efficient use of resources when making
parallel requests for resources
– Files, external web services etc
• But no programmer in those languages
would use async logic if they didn't have to

Copyright © 2014 M/Gateway Developments Ltd
Async is the New Sync?
• Why would Node.js developers use
asynchronous logic in Lambda functions if
they don't have to?
– Partly dogma

Copyright © 2014 M/Gateway Developments Ltd
Async is the New Sync?
• Why would Node.js developers use
asynchronous logic in Lambda functions if
they don't have to?
– Partly dogma
– Partly because almost no synchronous APIs
exist, particularly for:
• Database integration
• Web/REST service access

Copyright © 2014 M/Gateway Developments Ltd
Such APIs are possible

Copyright © 2014 M/Gateway Developments Ltd
Such APIs are possible

Copyright © 2014 M/Gateway Developments Ltd
Any other way…
• To have your Node.js cake and eat it?
– Not everyone will want to use Lambda
• Would it be possible to create a locally-
available environment where my Node.js
code runs in an isolated container where
concurrency isn't an issue?

Copyright © 2014 M/Gateway Developments Ltd

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
qewd
ewd-qoper8-gtm
Cache/GT.M
ewd-document-store
Global
Storage
ewd-session
Express
HTTP(S)
Interface
Browser/RESTClient
Custom Worker
Module
ewd-qoper8
Constructed from a number of EWD 3 modules
Legacy
Code
WebSocket
Interface

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
qewd
ewd-qoper8-gtm
Cache/GT.M
ewd-document-store
Global
Storage
ewd-session
Koa.js
HTTP(S)
Interface
Browser/RESTClient
Custom Worker
Module
ewd-qoper8
Can also use Koa.js – next generation Web Server
Legacy
Code
WebSocket
Interface

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
qewd
ewd-qoper8-redis
Redis
ewd-document-store
Global
Storage
ewd-session
Koa.js
HTTP(S)
Interface
Browser/RESTClient
Custom Worker
Module
ewd-qoper8
Can even use Redis as if it was a Global Storage DB
WebSocket
Interface

Copyright © 2014 M/Gateway Developments Ltd
QEWD's Architecture
• Master Process
– Handles all incoming REST requests
• Via Express
• Queues and dispatches requests to worker
processes
• Worker Processes
– You define how large a pool of workers you
require
– Each worker handles just one request at a
time (unlike Node.js Cluster)

Copyright © 2014 M/Gateway Developments Ltd
Master Node.js Process
Queue
Queue
processor/
dispatcher
Incoming
Request
REST
HTTP
WebSocket
QEWD Architecture
Every incoming request
is passed from Express
and placed in a queue
No further processing
of requests occurs in
the master process

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Queue dispatcher is
invoked whenever a
request is added to
the queue

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
Worker process
started if none
available

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
qewd-ripple
Handler module
Redis/Cache/GT.M
QEWD &
application-specific
Modules loaded
and connected to
database:
Redis,
Cache, GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Request passed
to worker
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
Custom
Worker
Module
Worker flagged as Unavailable
Node.js Worker Process
Custom
Worker
Module
Begin processing message
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Unavailable / processing
Another incoming
request Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Node.js Worker Process
Master Node.js Process
Queue
Queue
processor/
dispatcher
Custom
Worker
Module
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
If worker pool size not exceeded,
another worker is started
and request passed to it
Redis/Cache/GT.M
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
If entire Worker Pool is busy:
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
If entire Worker Pool is busy:
New
requests
remain
in queue
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
As soon as a worker is available again,
a queued message can be passed to it
Unavailable / processing
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
Available
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Finished
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
A user's handler function signals
completion using the function:
finished(responseObject);
This returns the response
object to the master
process

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Finished
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
Node.js Worker Process
Custom
Worker
Module
And the response is
passed to Express which
returns it to the client
that sent the original request
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Available
Node.js Worker Process
Custom
Worker
Module
The finished() function
also automatically returns
the worker process back
to the available pool
So it can now handle
the next queued request
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Available
Node.js Worker Process
Custom
Worker
Module
Worker processes, once started,
are persistent
No start-up / tear-down cost
Workers will automatically close
themselves down if they are
inactive for more than a pre-set
threshold time period
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Available
Node.js Worker Process
Custom
Worker
Module
Worker processes only handle
a single request at a time
Completely isolated run-time
environment for handler functions
No need for concerns about
Node.js concurrency, so
synchronous APIs can be used
Redis/Cache/GT.M

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Available
Node.js Worker Process
Custom
Worker
Module
Redis/Cache/GT.M
Long-running or CPU-intensive
logic has no direct impact on
other worker processes

Copyright © 2014 M/Gateway Developments Ltd
QEWD Architecture
Master Node.js Process
Queue
Queue
processor/
dispatcher
Node.js concurrency is handled
by the master process.
100% asynchronous logic
The master process does
almost nothing
No CPU-intensive or long-
running tasks, so very
high-performance
All the work happens in the
isolated worker processes
Multiple
Concurrent
Incoming
requests

Copyright © 2014 M/Gateway Developments Ltd
Performance?
• ewd-qoper8 module in isolation:
– Handles the queue/master/worker architecture
• Raspberry Pi 3 Model B
– 4 core CPU
– Readily-available commodity item
– Low-cost
• Easily-replicable benchmark

Copyright © 2014 M/Gateway Developments Ltd
Performance
• ewd-qoper8 benchmark script provided:
– How many workers? 3
– How many messages? 500,000
– Create a steady state of messages added to
the queue as they're being processed:
• Add a batch of 622 messages at a time
• Wait 100ms between each batch
– Messages are sent to workers which echo
them straight back

Copyright © 2014 M/Gateway Developments Ltd
Performance
• 5,800 messages/second sustained
throughput
• Limiting factor is master process hitting
100% CPU
• Workers only 30% CPU, so plenty of
capacity to do real work at this rate

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• For the Java, Python or .Net developer
moving to Node.js, QEWD makes it a
much simpler, much less weird and scary
environment
– Asynchronous code only needed when
necessary for parallel execution:
• eg accessing multiple remote web services
• Quick and simple to install, configure and
deploy

Copyright © 2014 M/Gateway Developments Ltd
Unique features of QEWD.js
• Somewhat comparable to Apache
Tomcat:
– Application container
• Can host multiple applications from one
single instance of QEWD.js
– Can be a mixture of websocket, HTTP and
REST applications

Copyright © 2014 M/Gateway Developments Ltd
Unique features of QEWD.js
• High-level abstraction of
Redis/Cache/GT.M:
– Flexible Document Database
– Persistent JavaScript Objects
• Built-in very high-performance Session
database
– Using the above databases

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• Front-to-back JSON
• Browser communicates via JSON
messages
– Ajax or Web-Sockets
• Even the integrated database is
abstracted as persistent JSON
– Cache, GT.M or Redis
– Identical APIs, so apps can be effortlessly
migrated between databases

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• Looks after all the critically important parts
of a Web Application's back-end for you,
eg:
– Sessions
– Database cacheing
– Security
• Using tried and tested solutions
– Based on the previous-generation EWD
technology

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• Resilient / Audit mode
– When enabled, permanent record kept in the
database of:
• Queued requests
• Processing status
• Response(s)
– If QEWD restarted, database is examined for queued,
unprocessed requests
• Automatically re-queued
– Can specify retention period of database records

Copyright © 2014 M/Gateway Developments Ltd
QEWD.js
• Supports all browser-side JavaScript
frameworks
• Some cool tooling and support available
for React

Copyright © 2014 M/Gateway Developments Ltd
Ripple-OSI
• Open Source project in UK & Ireland
– Open Source stack for healthcare
• Based on OpenEHR back-end systems
– Browser-based, REST-ful UI
• Orientated around the needs of clinicians
• Initiative led by Dr Tony Shannon
• Middle tier was originally Java-based
– Now entirely replaced using QEWD
• Choice of GT.M or Redis as embedded database
– Used for cacheing OpenEHR data

Copyright © 2014 M/Gateway Developments Ltd
Federated Access to OpenEHR
Browser QEWD
GT.M or
Redis
ewd-qoper8
queue
qewd-ripple
Module
Express
OpenEHR
Server
AQL over
HTTP(S)
Worker
PulseTile
UI
OpenEHR
Server

Copyright © 2014 M/Gateway Developments Ltd
Few Moving Parts
• Unlike EHMP, RippleOSI has almost no
other moving parts apart from Node.js and
QEWD.js
• Simple installer script
• Can even install and run on a Raspberry
Pi!

Copyright © 2014 M/Gateway Developments Ltd
Ripple Foundation
• http://ripple.foundation/

Copyright © 2014 M/Gateway Developments Ltd