EWD 3 Training Course Part 42: The QEWD Docker Appliance

Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 42
The QEWD Docker Appliance
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

Docker?
• A technology that allows software to be
encapsulated inside an isolated container
• According to Docker themselves:
– "Docker containers wrap a piece of software in a
complete filesystem that contains everything needed
to run: code, runtime, system tools, system libraries –
anything that can be installed on a server. This
guarantees that the software will always run the
same, regardless of its environment."
– See https://www.docker.com/what-docker

QEWD Docker Container
• QEWD is available from the main docker.io
repository as a pre-built Docker container
– rtweed/qewd
• You can also build your own version using the
Dockerfile that is included in the QEWD
repository
– eg, if you wanted to apply your own customisations
– See https://github.com/robtweed/qewd/blob/master/docker/Dockerfile

Benefits of the QEWD Container
• Provided you've installed Docker, you
don't need to do any further installation
– Just run the container
• First time you do this, it will automatically download
it from docker.io

Benefits of the QEWD Container
• QEWD functionality without any "moving
parts" on your system
– eg no Node.js dependency clashes
• You don't even need Node.js installed on your
system
– You just define your handler modules
• Write JavaScript files and let the QEWD container
handle them
– Without Node.js having to even be present on your
system

QEWD Appliance
• Just the core QEWD engine
– Master process
– Worker processes
• Doesn't include the embedded database
– Currently designed to work with Redis only
• Using mapped volumes
– You can use Redis locally, in another
container or remotely

QEWD Appliance
• Normal QEWD Session management will
take place provided a Redis database is
available

QEWD Appliance
• Nothing you can do in a standard local
QEWD installation that can't also be
achieved by using the Dockerised version
– There's even a version for the Raspberry Pi!
• rtweed/rpi-qewd

QEWD Appliance
• "Out of the box" defaults
– Management password: 'keepThisSecret!'
– Worker pool size: 1
– Database: Redis listening on port 6379
• qewd-monitor application is included and
ready to run
– No other applications or APIs pre-defined

QEWD Appliance
• You can customise the configuration:
– Management password
– Server name (what appears in qewd-monitor's
banner)
– Worker pool size

QEWD Appliance
• By using Docker volume mapping, you can
make specific directories in your host
system available to the QEWD Docker
container
• In your host system you can therefore
define interactive QEWD applications:
– Static browser-side resources (HTML, JS,
CSS files)
– Back-end handler modules

QEWD Appliance
• You can also define routes within your host
system, to be used by the QEWD
Appliance
– For Web / REST service APIs

So let's try it out
• I'm going to use a Ubuntu Linux system
• However, Docker can be installed on most
platforms
– Windows
– Linux (all versions/flavours)
– Unix
– MacOS
– Even the Raspberry Pi!

Installing Docker on Ubuntu 16.04
• sudo apt-get update
• sudo apt-get install docker.io
• You can now use Docker
– By default, you'll need to run Docker
commands as sudo
– This can be modified. See:
– https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-16-04

Installing Docker on Raspberry Pi
• Just invoke the command:
curl -sSL https://get.docker.com | sh
• You can now use Docker on your
Raspberry Pi
– By default, you'll need to run Docker
commands as sudo

Some Quick Docker Tests
• Try running these to confirm that Docker is
properly installed and working on your
system:
– sudo docker version
– sudo docker info

Let's start a Redis Container
On Linux:
• sudo docker run -d --name redis -p 6379:6379 redis
• Runs as a daemon (-d)
• Exposes internal port 6379 (the default Redis port)
externally to the host as port 6379 (-p)
• First time you invoke this command, it will download and
install the Redis Docker container

Let's start a Redis Container
On Raspberry Pi:
• sudo docker run -d --name redis -p 6379:6379 hypriot/rpi-redis
• Runs as a daemon (-d)
• Exposes internal port 6379 (the default Redis port)
externally to the host as port 6379 (-p)
• First time you invoke this command, it will download and
install the Redis Docker container

Test Redis
• First install the Redis command line tool:
– sudo apt-get install redis-tools
• Now start the Redis command line:
redis-cli
• It should respond with
127.0.0.1:6379>
– it's working and you're connected to the Redis container!
• Try the command:
info
• Exit redis-cli by typing CTRL&C

Prepare for the QEWD Appliance
• First important step:
– Create a directory for mapping the QEWD working
directory
– It can be any directory you like. I'll use:
cd ~
mkdir qewd
– Now make a sub-directory named modules
cd qewd
mkdir modules
• You don't need to put anything into this directory
yet, but it should exist

Start the QEWD Appliance
sudo docker run -d -p 8080:8080 --link redis:redis -v /home/ubuntu/qewd/modules:/opt/qewd/mapped rtweed/qewd
First time you invoke this, it will download the QEWD Container from
Docker.io
-p 8080:8080 maps port 8080 in the QEWD container to your host's port 8080
-d run as a daemon. You can also try -it for interactive display
-link redis:redis links to the Redis container
-v maps the QEWD working directory to the one we created
QEWD will now be running!
On Linux:

sudo docker run -d -p 8080:8080 --link redis:redis -v /home/pi/qewd/modules:/opt/qewd/mapped rtweed/rpi-qewd
First time you invoke this, it will download the QEWD Container from
Docker.io
-p 8080:8080 maps port 8080 in the QEWD container to your host's port 8080
-d run as a daemon. You can also try -it for interactive display
-link redis:redis links to the Redis container
-v maps the QEWD working directory to the one we created
QEWD will now be running!
On Raspberry Pi:

Try QEWD
http://192.168.1.123:8080/qewd-monitor/index.html
Change the IP address / host name as appropriate for your host machine
You should see the qewd-monitor application!
Log in using the default password: keepThisSecret!

Let's check Redis again
• Start redis-cli again
• This time enter the command:
– keys *
• You should see a load of Redis key/value
pairs, representing the QEWD Session
global storage used by your qewd-monitor
session

Let's build a quick application
• We'll create the files in the ~/qewd
directory that we previously made

First, stop the QEWD Container
• Use the qewd-monitor; or
• Use the docker stop command
– To do that we need to first find out the QEWD
container's unique Id
– sudo docker ps -a
CONTAINER ID IMAGE
d810c520894e rtweed/qewd
7d0c18b8cec5 redis

First, stop the QEWD Container
• Use the qewd-monitor; or
• Use the docker stop command
– To do that we need to first find out the QEWD
container's unique Id
– sudo docker ps -a
CONTAINER ID IMAGE
d810c520894e rtweed/qewd
7d0c18b8cec5 redis Usually the first
3 characters are
sufficient

Stop the QEWD Container
• sudo docker stop d81

Create a test application
• We'll name it testapp
– It will have a button which, when clicked,
sends a message to the QEWD back-end
which returns an acknowledgement response
• First create a directory for the browser-
side static files:
cd ~/qewd
mkdir www
cd www

Create the index.html
<html>
<head>
<title>Demo QEWD application</title>
</head>
<body>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.2.0/jquery.min.js"></script>
<script src="/socket.io/socket.io.js"></script>
<script src="/ewd-client.js"></script>
<script src="app.js"></script>
<button id="testBtn">Click Me</button>
<div id="content">
Content goes here
</div>
</body>
</html> Save as ~/qewd/www/testapp/index.html

Create the app.js
Save as ~/qewd/www/testapp/app.js
$(document).ready(function() {
EWD.log = true;
EWD.on('ewd-registered', function() {
$('#testBtn').on('click', function(e) {
var message = {type: 'testButton'};
EWD.send(message, function(messageObj) {
$('#content').text(messageObj.message.ok);
});
});
});
EWD.start('testapp', $, io);
});

Create the back-end module
• This needs to go into the directory we
created earlier:
~/qewd/modules
• We'll name the module testapp.js

Create testapp.js
module.exports = {
handlers: {
testButton: function(messageObj, session, send, finished) {
console.log('*** handling the button click message!');
session.data.$('foo').value = 'bar';
finished({
ok: 'testButton message was processed successfully!'
});
}
}
};
Save as ~/qewd/modules/testapp.js

How will QEWD find the module?
• The QEWD Docker Appliance will expect
to find it in its node_modules directory
• We don't have access to that from the host
• But we've mapped ~/qewd/modules to a
mapped volume in the Docker container:
~/opt/qewd/mapped

How will QEWD find the module?
• We can use a QEWD module map to tell
QEWD where to find the back-end module
for our testapp application
• The QEWD Docker appliance allows us to
define this in the mapped volume directory
using the reserved file name:
– moduleMap.js

Create moduleMap.js
module.exports = {
testapp: '/opt/qewd/mapped/testapp'
}
Save as ~/qewd/modules/moduleMap.js

Create moduleMap.js
module.exports = {
}
The module map exports as many mappings as you want

Create moduleMap.js
module.exports = {
}
The module map exports as many mappings as you want
We just need this one.

Create moduleMap.js
module.exports = {
}
Note: the mapped module path is to the internal path
within the container

Create moduleMap.js
module.exports = {
}
Note: the mapped module path is to the internal path
within the container, not the path we created on the host
~/qewd/modules/testapp.js

That should be all we need
• When we start the QEWD Appliance
again, we must also map the directory
containing the browser-side files, ie
– ~/qewd/www/testapp

• On Linux:
sudo docker run -d -p 8080:8080 --link redis:redis ↩
-v /home/ubuntu/qewd/modules:/opt/qewd/mapped ↩
-v /home/ubuntu/qewd/www/testapp:/opt/qewd/www/testapp ↩
rtweed/qewd

• On Raspberry Pi:
-v /home/pi/qewd/modules:/opt/qewd/mapped ↩
-v /home/pi/qewd/www/testapp:/opt/qewd/www/testapp ↩
rtweed/rpi-qewd

Try running testapp
It works
The console show that
testapp correctly registered
itself on QEWD
Try clicking the button..

Try running testapp
It works too!
A message was sent
to the QEWD back-end
which returned the expected
response

Check the Session
Start the qewd-monitor application and click the Session tab:

Check the Session
Start the qewd-monitor application and click the Session tab:
Where did this come from?

It came from testapp.js
module.exports = {
handlers: {
testButton: function(messageObj, session, send, finished) {
console.log('*** handling the button click message!');
session.data.$('foo').value = 'bar';
finished({
ok: 'testButton message was processed successfully!'
});
}
}
};
Save as ~/qewd/modules/testapp.js

QEWD Apps with no moving parts!
• We just created a QEWD app without
having anything installed other than
Docker
• We just defined:
– the HTML and JavaScript files for the
browser
– The back-end JavaScript handler module
• And mapped their directories as Docker
volumes

Adding more apps
• Each app you create will need its own
subdirectory under the ~/qewd/www directory
– For its browser-side HTML, JavaScript, etc files
– Each of these will have to be mapped to the
corresponding volume in the QEWD container
• Their back-end modules, however, just go into
your mapped ~/qewd/modules folder
– And then define their module mapping in
moduleMap.js

Mapping Multiple Apps
module.exports = {
testapp: '/opt/qewd/mapped/testapp',
mySecondApp: '/opt/qewd/mapped/mySecondApp',
myThirdApp: '/opt/qewd/mapped/myThirdApp'
}
~/qewd/modules/moduleMap.js

Mapping Multiple Apps
• eg, On Linux:
-v /home/ubuntu/qewd/modules:/opt/qewd/mapped ↩
-v /home/ubuntu/qewd/www/testapp:/opt/qewd/www/testapp ↩
-v /home/ubuntu/qewd/www/mySecondApp:/opt/qewd/www/mySecondApp ↩
-v /home/ubuntu/qewd/www/myThirdApp:/opt/qewd/www/myThirdApp ↩
rtweed/qewd

What about REST APIs?
• We can use the QEWD Docker Appliance
to very quickly create REST APIs, again
without any moving parts other than
Docker itself
• Even simpler to create than applications

Let's create an API
• We'll define a URL path prefix:
– /api
• And handle any lower-level URLs, eg:
– /api/test
• To do this we just need to create a handler
module for the /api path. We'll call it api.js. It
must be saved into the ~/qewd/modules
directory

Create api.js
module.exports = {
restModule: true,
handlers: {
test: function(messageObj, finished) {
finished({foo: 'bar'});
}
}
};
Save as ~/qewd/modules/api.js

Create api.js
module.exports = {
restModule: true,
handlers: {
}
}
};
Save as ~/qewd/modules/api.js
It's just a standard QEWD REST/Web Service Module

Create api.js
module.exports = {
restModule: true,
handlers: {
}
}
};
This function, test, will handle
any incoming /api/test requests

QEWD needs to know how to find it
• As we're defining the handler module in a
mapped directory, we need to tell QEWD
where to find it and how to define it as a
route.
• For this we define a reserved named file in
our ~/qewd/modules directory:
– routes.js

Create routes.js
module.exports = [
{
path: '/api',
module: '/opt/qewd/mapped/api'
}
];
Save as ~/qewd/modules/routes.js

Create routes.js
module.exports = [
{
path: '/api',
}
];
Save as ~/qewd/modules/routes.js
You export an array of route objects
We'll just define one for /api in this example,
but you can define as many routes as you wish

Create routes.js
module.exports = [
{
path: '/api',
}
];
Note that the route must map to the container's
internal mapped volume path
So any incoming requests with a URL starting
/api will be handled by the api.js file we've created
in the host's mapped directory

Let's try it
• Our handler function isn't making any
distinctions about the HTTP method used,
so we can test it just using a browser.

Let's try it
It worked!

REST/Web Service APIs
• Of course this was a very simple example
• But you can write as complex APIs as you
wish.
• All the functionality described in parts 31
and 36 of this course are available in the
QEWD Docker Appliance

REST APIs without moving parts
• You can now define Web/REST APIs by
writing JavaScript handler module files
• No need to install Node.js

Customising QEWD Appliance
• QEWD Docker Appliance defaults:
– Management password: keepThisSecret!
• Always a good idea to change this!
– Server name: QEWD Docker Server
• Used by the qewd-monitor application
– Worker pool size: 1
• You can change these

Customising QEWD Appliance
• Create a file named custom.js in your
mapped directory (eg ~/qewd/mapped)
– custom.js is a reserved name that the QEWD
Docker Appliance will look for and use for
customising its configuration

Create custom.js
module.exports = {
config: {
managementPassword: 'mySecret!',
serverName: 'Robs QEWD Docker Appliance',
poolSize: 2
}
};
Save as ~/qewd/modules/custom.js

Restart the Appliance
• eg:
– sudo docker restart d81
• Try running qewd-monitor
– You'll need to use your new custom login
password
– It will display the new name for your server
– It will show 2 worker processes

Further Customisation
• You can get access to the master process
objects:
– Create user defined data / objects that are
passed to worker processes
– Access the ewd-qoper8 object
– Access the Express object
• Define a run function. This is invoked
when QEWD starts.

Create custom.js
function customise(config, q, intercept) {
console.log('*** This is the custom function calling!');
}
module.exports = {
config: {
run: customise,
poolSize: 2
}
};
Save as ~/qewd/modules/custom.js

Create custom.js
function customise(config, q, intercept) {
console.log('*** This is the custom function calling!');
}
module.exports = {
config: {
run: customise,
poolSize: 2
}
}; q is the main ewd-qoper8 object
intercept.app is the Express object
allowing you to add custom middleware

That's the QEWD Docker Appliance
• A handy and simple, low-impact way of
using QEWD without worrying about
interactions with your existing set-up
– And without having to install Node.js or a
database
• All the functionality of a standard local
implementation of QEWD is still available
to you

EWD 3 Training Course Part 42: The QEWD Docker Appliance

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EWD 3 Training Course Part 42: The QEWD Docker Appliance