Back-end (Flask_AWS)

Back-end Development
Intro to AWS and Flask

Rough Plan (please add to this, it is just some rough
ideas I had)
Me:
intro to AWS slides
○ What it is
○ why should you learn about it
○ AWS services
○ pricing
○ what is RDS
● Setting up an RDS database
● me connecting to it
● set up AWS user and permissions for Milind to connect
Milind stuff
● slides talking about what flask is, what it’s used for, flask basics, quick recap on HTTP methods (don’t really need to go into detail just
maybe say what for example a POST request is used for generally and give an example of a complete POST request (an example
payload, and response) , maybe just list out all the SQL commands we are going to use ahead of time on the slides just so they don’t
get overwhelmed when they see them in the code). They should have some exposure to SQL because of the WISC sql workshops
though), etc
● Make a REST api with endpoints GET api/articles/:id, GET api/articles/, POST api/articles, /PUT api/articles/id (let’s use ‘articles’
instead of posts to make it less confusing (HTTP post vs an actual post)
● a post consists of three things: title, body, author (let’s avoid using images to avoid unnecessary complexity)
● push your stuff to a git repository

● Basically just a bunch of servers that can be accessed through the internet
● For example.
○ Ex. you could be storing documents in the cloud if you use
OneDrive/Google Drive/etc
○ If you run your python program on Google’s servers, you can say that
you are running your python program in the ‘cloud’
What is the cloud?

What is AWS?
● Amazon Web Services (AWS) is a cloud service provider
● on-demand delivery of IT resources over the internet
● Examples of it’s services include:
○ Elastic Compute Engine (EC2) - virtual machine
○ Relational Database Service (RDS) - database
○ Amazon S3 - cloud object storage
○ Over 200 more!
● Anything your app needs, AWS probably has a service to help you!
○ youtube.com/watch?v=JIbIYCM48to

Why learn AWS?
● AWS is the leading cloud service provider in the world
● Used by companies like Netﬂix, Sony, Disney, Nasa, Epic Games, Reddit, etc .
● It’s an extremely useful skill to have on your resume!
source:https://www.statista.com/chart/18819/worldwide-market-share-of-leading-cloud-infrastructure-service-providers/:

Benefits of using the cloud
● Trade capital expense for variable expense
● Don’t need to know how much hardware you need upfront
● Increase Agility ex. only takes a couple clicks to launch a website
● Extremely easy to deploy your products globally
● Beneﬁt from massive economies of scale -> costs less to do stuﬀ in the cloud!
● Don’t need to maintain hardware anymore!
From a software engineering POV

What we’ll be doing in today’s workshop
REST API (running
on AWS EC2)
Database (running
on AWS RDS)

● “A software intermediary that allows two applications to talk to each other.”
● How can the front-end get data from the back-end?
What is an API
?

What’s an API’s purpose?
● We could let the front-end deal with all the complexity of retrieving the data
○ i.e connecting to database, querying the database, structuring/ﬁltering
the data that came from the database, etc
What is an API? continued

What is an API? continued
What’s an API’s purpose?
● Better way:
○ Front-end send requests to speciﬁc ‘endpoints’ on the back-end and
waits for data to be sent back
■ Ex. http://some-server/api/cats
■ Ex. http://some-server/api/users/2
○ Let the back-end deal with all the internal complexity!
○ Similar to how we create public interfaces with classes in languages
like Python/Java/etc (users need to know what’s going on internally in
class, we can just use its methods and attributes)

● Say I want to retrieve some data about all the users of my application
● I can just send a GET request to http://my-server/api/users and I will get
back some data like this:
●
[
{
ﬁrst_name: “Bobby”,
last_name: “Daniels”
},
{
ﬁrst_name: “Paul”,
last_name: “Smith”
}
[
For example...

HTTP Request Methods
GET: Retrieve a resource (some data) on the server
POST: Create a new resource on the server
PUT: Update a resource on the server
DELETE: Delete a resource
etc.
and when to use each

Quick Demo of what we will be making

AWS Services that we will be
using today to make it

EC2 = Elastic Compute Engine
● A virtual machine that runs on AWS’ physical servers
● You can run any OS you want on it, including Ubuntu, Amazon Linux,
MacOS, WIndows, etc.
● You can upgrade an EC2 instance to whatever specs you’d like (including
memory, cpu, storage)
● Examples of what you can do:
○ Run demanding tasks (maybe training a ML model, performing large
scale data analysis, etc)
○ Host a minecraft server
○ Do (almost) anything you could with a normal computer!
AWS EC2

RDS = Relational Database Service
● A managed PostgreSQL/MySQL/Oracle/etc database
● Some cool features of this service
○ Oﬀers automatic database backups
○ Auto-scaling (the database can scale up and down in terms of its
processing power depending on the current demand)
○ etc.
AWS RDS

A security group acts as a ﬁrewall that controls what gets in and out of your
EC2/RDS/etc instances.
Example:
AWS Security Group

AWS VPC
VPC - Virtual Private Cloud
● Your own private network within AWS
● A logically isolated section of the AWS Cloud where you can launch AWS
resources in a virtual network that you deﬁne
● Don’t worry about this for this workshop!

Let’s set up a Database on AWS!

Flask is Python based lightweight framework used to
build web applications.
We will be using Flask to make an API today.
API (Application Programming Interface) is an application
that provides an interface so that the database and the
frontend can interact. API uses HTTP request to
communicate with frontend.
Python Flask

200 OK: The response has succeeded!
201 Created: The request has succeeded, and the resource has been created (usually for POST)
400 Bad Request: The server could not understand the request due to invalid syntax
401 Unauthorized: The client is not allowed to get the requested response
404 Not Found: The server cannot find the requested resource
418 Unprocessable Entity: The server unable to process the contained instructions.
500 Internal Server Error: The server has encountered an issue while processing your request
HTTP Request

We can make diﬀerent types of requests: GET, POST, PUT, PATCH, etc
Example:
POST /articles
{
author: ‘gdsc’,
title: ‘welcome to apis’,
body: ‘blah blah blah’
}
Making a request

Allows you to use ORM (Object Relational mapping), which provides an interface
for using OOPs to interact with database.
This allows you to not write raw SQL
Flask SQLAlchemy
db.Model Ability to create and manipulate models/tables
db.session Ability to create and manipulate transactions/queries
db.session.add(person) It is used as an insert SQL Query
db.session.commit() It is used to run the transaction

Model is a description of the database table in ‘class’ form. This helps
SQLAlchemy map the database table to an object.
Serialization is converting the object in a more readable form.
For example:
<Article 1> is an object of article but you don’t want to send the object itself so
you convert this object to something like:
{
title: ‘welcome to gdsc’,
body: ‘blah blah blah’
}
Model and Serialization

Useful functions
MyModel.query Used to return the query table
MyModel.query.filter_by(<expression>)
eg : name = 'Milind'
Used to filter the query object and return
only the one/many you asked for
MyModel.query.filter(<expression>)
eg: Person.name ="Milind", Team.name = "Pod7"
More flexible to use like filter_by method
MyModel.query.first() Used to get the first result of a query/list of
responses
MyModel.query.all() Used to get all the results of a query
MyModel.query.limit(<number>).all() Used to get a limited number of response
Note that “MyModel” is just some arbitrary model that we made up for this slide

api.py (used to create the endpoints)
Basics
model.py (used to describe the database)

IF YOU START UP ANY AWS RESOURCES,
PLEASE REMEMBER TO DELETE THEM
WHEN YOU ARE DONE USING THEM. WE
ARE NOT RESPONSIBLE FOR ANY
FINANCIAL LOSSES if you forget to do
this :)))

Back-end (Flask_AWS)

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