Google App Engine for Beginners

Google App Engine
for beginners
...and a peek on experimental features
Alessandro Bahgat
@abahgat
Appsterdam Guru Session, June 25th 2013

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What is Google App Engine?
Google App Engine is a complete development
stack that uses familiar technologies to build and
host applications on the same infrastructure used at
Google.
@abahgat, #appsterdam
“
”
2/46

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Four runtime environments
Python Java
Go PHP
@abahgat, #appsterdam 3/46

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Your code runs in a sandbox
http://www.flickr.com/photos/damongman/5623130732/

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The Sandbox
Secure environment that provides limited access to the underlying operating
system.
The sandbox allows App Engine to
distribute web requests across multiple servers
start and stop servers to meet traffic demands
isolate apps in a secure, reliable environment
abstract hardware, operating system and physical location of the web server
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5/46

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Sandbox limitations
outbound connections: only through the provided URL fetch and email
services or the experimental Socket API.
inbound connections: only HTTP(s) on ports 80/443.
filesystem access: writing files is not allowed. An application can read only
files uploaded with the application code.
no native code: libraries that depend on native code are generally not
available.
time limits: app code must terminate within given time limits. (60s for web
requests, 10m for tasks but unlimited time for backend jobs)
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Storing data
Three options for data storage
App Engine Datastore a NoSQL
schemaless data storage built in
GAE
Google Cloud SQL: a relational SQL
database service similar to MySQL
Google Cloud Storage: file based
storage

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No fixed costs: pay only for what you use...
http://www.flickr.com/photos/jasonalley/5039425430

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...with generous free quotas
http://www.flickr.com/photos/toddle_email_newsletters/7002322316

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Getting app & running
See it in action

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Download the SDK
Go to https://developers.google.com/appengine/downloads and grab the
Python installer.
You should also have Python by now, but in case you do not, grab it from here.
(Your platform might offer smarter ways to install it.)

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Start up the launcher

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Create a sample application

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Run!
http://www.flickr.com/photos/nihonbunka/46324600

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Let's dive into code
Basics of the Python Runtime

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Application Configuration
All configuration settings are stored in a file called a
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16/46

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A self sufficient web application
App Engine supports webapp2 by default:
In addition to webapp2, the environment includes WebOb and Django.
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17/46

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Datastore(s)
There are two implementations of datastore
The original one is implemented in g
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The new one is called NDB and it is implemented in
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They are very similar but not identical
We will cover NDB
·
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·
·
·
18/46

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Datastore
Creating an entity type is as easy as creating a Python class.
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19/46

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Querying the Datastore
The Datastore API is Object Oriented.
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Queries are objects
Filters and projections are specified by calling methods
Make sure you know the limits! (Read the docs)
·
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20/46

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Querying the Datastore with GQL
You can write queries with GQL, a SQL-like language.
GQL is translated to NDB's native query API. (This is the opposite of what
traditional ORM libraries do!)
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21/46

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View templates
If you use webapp2, Django templates are supported by default.
Alternatively, App Engine ships with jinja2, too.
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22/46

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Dispatch to view templates
Here is how to render a template in with webapp2:
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23/46

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Memcache
Memcache is a high-performance, distributed memory object caching system.
Can be used to minimize hits to the Datastore or to save transient state
information.
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24/46

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Hands-on exercises
You will have to do some work now ;)

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Preparation
Download the boilerplate code from here
Uncompress it
Open it up in a text editor/IDE you are familiar with
Take some time to familiarize with it
·
·
·
·
26/46

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Exercise 1
(Quasi) Real Time Communication

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Implement a backend for the page below

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Your mission
Use the Channel API to show the cursor position of every visitor's mouse.
Update the cursor position whenever users move their mouse.
Remove cursor icons when visitors leave the page.
Complete the code in the c
h
a
n
n
e
l directory of the package you downloaded
earlier and implement the missing methods.
Point your browser to h
t
t
p
:
/
/
l
o
c
a
l
h
o
s
t
:
$
A
P
P
_
P
O
R
T
/
c
h
a
n
n
e
l to test your
server.
·
·
·
·
·
29/46

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Channel API
A channel connects two ends:
A client, which
A server, which
·
connects to a channel,
listen for updates,
sends messages to the server.
-
-
-
·
maintains a registry of open channels,
notifies clients of state changes.
-
-
30/46

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The role of the Server
There is a service for that! Enable presence in your a
p
p
.
y
a
m
l
and implement two handlers that can respond to P
O
S
T at
The server needs to keep track of the connected clients,
you can keep that information in memcache but
for this example, it is necessary to be notified of connections and
disconnections.
·
·
·
i
n
b
o
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d
_
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v
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:
- c
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/
d
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c
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d
/
·
·
31/46

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Creating a Channel
Requires action on both ends. The server sends a token to the client:
The client uses the token to create a channel
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t = "
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;
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)
;
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(
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.
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p
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n
(
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;
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t
.
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s
s
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e = o
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;
}
J
A
V
A
S
C
R
I
P
T
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Using the Channel
The client can only read messages from the client.
It can send data to the server via HTTP requests:
f
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c
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n o
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)
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* d
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}
J
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;
}
J
A
V
A
S
C
R
I
P
T
33/46

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Exercise 2
Building an API Backend

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Implement a backend for the page below

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Your mission
Complete the code in the e
n
d
p
o
i
n
t
s directory of the package you
downloaded earlier and implement the missing methods.
Point your browser to h
t
t
p
:
/
/
l
o
c
a
l
h
o
s
t
:
$
A
P
P
_
P
O
R
T
/
e
n
d
p
o
i
n
t
s to test
your server.
·
·
36/46

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Google Cloud Endpoints (experimental)
Google Cloud Endpoints consists of tools, libraries and capabilities that allow
you to generate APIs and client libraries from an App Engine application.

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Create a service
Annotate the API implementation class with the endpoints decorators,
create an API server instance,
and map the instance to the API URL
@
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38/46

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Define the API methods
Annotate methods with
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·
·
·
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Some closing notes on Endpoints
Apps that use Cloud Endpoints expose discovery services at
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You can use the SDK to generate JavaScript, Android and iOS clients for your
service,
Endpoints can authenticate clients using OAuth 2.0,
If you want to build a REST API, check out Endpoints Proto Datastore,
and if you work with Android applications, check out the Mobile Backend
Starter.
·
·
·
·
·
·
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There's more

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A few more advanced APIs
XMPP – Integrate your app with Google Talk and Instant Message Clients.
Search (experimental) – Build indexes for fast search over sets of document
(which can be any object your app manipulates. Supports full text search and
distance-based geographical search out of the box.
Prospective Search (experimental) – Analyze a real-time feed of documents
and be notified when anything matches one of your searches.
·
·
·
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Take your app to the next level
http://www.flickr.com/photos/msimdottv/4339697089

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Time for a Challenge
Using the Search API to build a map-based application

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Advanced Search
Using the Search API, build a location aware system.
Search for all the points that are closer than 10km from my position.
Run a full text search on the items descriptions.
·
·
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g+ plus.google.com/107973517098181615920
twitter @abahgat
www www.abahgat.com
github github.com/abahgat

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Google App Engine for Beginners

Google App Engine for Beginners

Alessandro Bahgat

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