COMP3207 - Cloud Application Development

Cloud Computing Overview

Cloud Computing: the delivery of on-demand system resources, particularly data storage and computing power, without direct management by the user

• large clouds often provide functions distributed over several servers
• clouds can belong to an organisation or be public
• cloud computing relies on the sharing of resources to achieve coherence and scale
• cloud computing reduces infrastructure costs
• cloud computing improves speed, performance, and management
  

A Cloud Service Provider is a third-party company offering a cloud-based platform, infrastructure, application, or storage service. Examples of CSPs are Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform.

• Cloud Providers need to:

• enable self-service access
• manage the infrastructure the cloud runs on

• The Cloud needs to meet requirements such as:

• virtualisation
• automation
• standardisation
• service management
  

Serverless Architectures

Serverless: cloud computing execution model where the cloud provider runs the server and dynamically manages resource allocation

• abstraction of servers
• event-driven applications
• instant and automatic scalability
  

Serverless means that code runs only on-demand and on a per-request basis.

• API requests are sent by consumers
• Objects are retrieved, created, or moved in storage
• Events are scheduled

Frontend: frontend infrastructure includes everything the end user interacts with, and makes up the user interface. This includes components such as local networks, web browsers, and web applications

• User Interface - refers to all components the end user can access, to send requests or perform actions
• Software - runs on the end user's machine and is comprised of client-side applications and browsers
• Network - the end user's machine. This can be mobile or PC and should work regardless of computing power

Backend: backend architecture is comprised of hardware and storage located on servers, and powers the frontend architecture

• Application - manages requests and requirements made by the user and provides functionality to the user interface
• Service - manages resources on servers such as tasks, storage, and computing
• Runtime - the virtual environment where services such as apps, servers, storage, and networks are run
• Storage - location where data is stored. This can be a HDD, SSD, flash drive, RAID storage, etc. Data is partitioned in storage for accessibility and redundancy
• Infrastructure - engine managing all the services, which has a CPU, GPU, motherboard, network cards, input and output
• Management - middleware which allocates resources to specific tasks and communicates between frontend and backend
• Security - safety of data via redundancy and backups, as well as safety of networks via firewalls and protocols

Amazon Web Services

AWS Lambda: event-driven, serverless platform provided by Amazon as part of Amazon Web Services

• FaaS platform which provides fully managed infrastructure
• Automatic management of resources and servers
• Automatic scaling
• Smart billing based on executions, not server instances
• Rapid development and deployment
• Services that are event-driven and instantaneously scalable
• Monolith vs microservices approach
• Cost, usage, and scale are reduced while complexity is increased
• DevOps methodology is used which shortens the development lifecycle while also delivering features, fixes, and updates frequently in alignment with business requirements

 

 

 

 

 

 

 Microsoft Azure

Microsoft Azure: cloud computing service for developing, testing, deploying, and managing web applications through Microsoft servers

• SaaS, PaaS, and IaaS
• Provides IaaS virtual machines which allow users to launch Windows, Linux, and other popular disk images
• Provides PaaS app services letting developers publish and manage web applications easily
• Azure Websites allows developers to build sites using ASP.NET, PHP, JavaScript, or Python and can easily be deployed or uploaded through the user portal  
• WebJobs applications can be deployed to an App Service environment to implement background processing which can be performed on schedule, on demand, or continuously
• Links to SaaS services such as Office 365

 

 

 

 

 

 
 Google App Engine

Google App Engine (GAE): cloud computing platform for developing and hosting web applications in Google data centers

• Provides PaaS app services letting developers publish and manage web applications easily
• Language support for Go, PHP, Java, Python, Node.js, .NET, and Ruby
• Framework support including Django, Pyramid, Flask etc.
• Integration with Google Cloud Platform, a suite of cloud computing services including computing, storage, analytics, and machine learning
• Support for Flask, a Python micro-framework providing tools, libraries, and technologies for building web applications
• Support for Django, a Python framework handling authentication, content, site maps, RSS, templates, REST etc.
• Support for Firebase, a BaaS app development framework providing data storage, functions, machine learning, authentication, hosting, analytics, testing, messaging etc.

 Development Life Cycle:

• Application development
• Application testing
• Administration
• Deployment
  
   
  

JavaScript

Node.js: open-source, cross-platform, backend JavaScript runtime environment built on Chrome's JavaScript engine which executes JavaScript code locally.

• uses event-driven I/O to remain lightweight and efficient
• uses traditional web-serving techniques to create new threads for connections
• operates on single-thread I/O calls, allowing it to support tens of thousands of concurrent connections
  

Variables

JS has three kinds of variable declarations:

• var declares a global or local variable
• let declares a local variable
• const declares a read-only constant

 Data Types

 JS uses the following eight data types:

JS is dynamically typed - values are typed but variables are not

 Conditional Statements

• If/else statements
  
   if (condition1) {
  
   statement1;
  
   } else if (condition2) {
  
   statement2;
  
  } else {
  
   statement3;
  
   }
  
• Switch statements
  
   switch (expression) {
  
   case value1:
  
   statement1;
  
   break;
  
  
   case value2:
  
   statement2;
  
   break;
  
  
   default:
  
   statement;
  
   break;
  
   }
  
    

Loops & Iteration

• For loops (previously covered)
• Do-While loops (previously covered)
• While loops (previously covered)

• For-Of Iterators
  
   var array = [1,2,3];
  
   for (let i of array) {
  
   statement;
  
   }
  
• For-In Iterators
  
   var object = {age:20,height:1.63};
  
   for (let k in object) {
  
   statement;
  
   }
  
  
  

• For-Each Iterators
  
   array.forEach(x => x + 1)
  
  
   Exceptions
  
• Try/Catch blocks
  
   try {
  
   var input = "hello";
  
   var value = parseInt(input);
  
   } catch (e) {
  
  alert("Error")
  
   }
  
  
• Throw statements
  
   throw("exception thrown");
  
  
   Operators
  
• JS supports the following basic operators:

• Conditional operators
  
   condition ? true value : false value
  

Collections

• Arrays
  
   myarray = [1,2,3];
  
   myarray[0] = 10;

Functions

• Simple Functions

 
 function square(number) {

 return number*number;

 }

• Anonymous Functions
  
   const square = function (number) {
  
   return number*number
  
   }
  
• Lambda Functions
  
   number => number*number;
  
   array.sort((a,b) => ((a > b) ? 1 : 0))
  
  
• Rest parameter syntax allows an indefinite number of arguments in a function
  
   function multiply(multiplier, ...args) {
  
   return args.map(x => multiplier * x);
  
   }
  
  

Higher Order Functions

 

 Object Functions
 

 JavaScript in Web Pages

Document Object Model (DOM): formal API which abstracts the elements of HTML into a hierarchical structure consisting of nodes accessed by standard methods

• Finding all text paragraphs

document.querySelectorAll("p")

• Finding all the HTTP URLs
  

allA = document.querySelectorAll("a")

allURLs = Array.from(allA).map(a => a.getAttribute("href"))

allHTTPURLs = allURLs.filter(u => u.startsWith("http"))
 

 

Asynchronous Programming

Asynchronous Programming: method of parallel programming where tasks can run separately to the main application thread and communicate their completion, failure, or progress

• JS can be used to update a date in a web page

• given the date code

<p class="credits"> <date>2013</date>…

• select the date text content

document.querySelector("date").textContent

• check it against the current date

new Date().getFullYear()

• put it all together

function checkdate() {

 if (document.querySelector("date").textContent == new Date().getFullYear())

 alert("correct");

else alert("incorrect");

 }

• call it only after the page has loaded

window.onload = checkdate
  
 Callbacks & Promises
  
 Callback: function which executes after another function is complete

• a function passed into another function is called a callback
• callbacks are executed after other functions are complete
• functions which accept callbacks as parameters are called higher-order functions
• callbacks ensure code executes in the correct order

Callback declaration:

 function addOne(number, callback) {

 alert(number +1);

 callback();

 }

 addOne(1, callback);


 Promise: alternative to a callback which represents the result of an asynchronous operation

 A promise can be pending, fulfilled, or rejected:

• Pending: state showing the initial state of a promise
• Fulfilled: state showing a successful operation
• Rejected: state showing a failed operation
  

Promise declaration:

• the function passed to the new promise is the executor
• the executor contains producing code which outputs a result
• the executor starts automatically on creation
  
   promise = new Promise(function(resolve, reject) {
  
   statement;
  
   });
  
    
• resolve(value) indicates the job has completed successfully

• sets the state to "fulfilled"
• sets the result to value

• reject(error) indicates an error has occurred

• sets the state to "rejected"
• sets the result to error

Promises can be connected to consuming functions such as then and catch:

• Then function

• function(result) runs when the promise is resolved
• and receives the result
• function(error) runs when the promise is rejected
• and receives the error
  
   promise.then(function(result) { statement; }, function(error) { statement; });
  

• Catch function

• catch is used if you're only interested in errors
• is a shorthand method of omitting the result function
  
   promise.catch(alert);
  
   OR
  
   promise.then(null,alert);
  
• to omit the error function, promise.then can be shortened
  
   promise.then(alert);
  
   OR
  
   promise.then(alert,null);
   
  

Software Development Practices and Tips
 
 Practices for Software Development

 What are the barriers to writing good code?

• functional goals often take precedence
• a lot of software development is self-taught
• progress can be slow when developing applications
• wide variety of frameworks and practices

Technical Debt: implied cost of additional work caused by choosing an limited solution rather than a more complex approach

• like financial debt, code gathers interest over time
• debt is paid off in maintenance
• if not maintained, software is unable to evolve
  

Maintainability: ease with which a software system or component can be modified to correct faults, improve performance, or adapt to a changed environment

• adding new features, without introducing bugs
• fixing bugs, without introducing new bugs
• improvement in performance and usability
• improvement in productivity
• support for multiple environments
• easier collaboration
  

Top Tips for Software Development

• Get the requirements right

• Decide what you are building and who it is for
• Most errors are introduced during requirements analysis and design
• Leaving errors in code reduces maintainability and increases technical debt

• Write code assuming others will see it

• Use comments in code
• Use consistent-looking code
• Use code analysis tools e.g. pycodestyle, pylint, flake8

• Write code assuming others will run it

• Provide an automated build process
• Provide a test suite
• Automate install, build, and test together
• Provide infrastructure support

• run and install overnight
• email reporting
• continuous integration

• Get others to check code

• Collaborate with other team members
• Focus on critical sections of code

• Use version control

• Use GitHub for version control

• allows easy backups and commits
• store code, documentation, unit tests, test data, custom scripts
• improves collaborative development