Server-side Technology

Architecture

• Webserver
  • Static (only serving content)
  • Static and configurable
  • Dynamic (static + application server)
• Storage System
  • SQL database
  • NoSQL database
  • Key-value store
  • Blob storage
  • File system

Web Server

Functionality

• Task:
  • Communicate with browser
  • Implement HTTP
• Possible architectures:
  • Process-based
  • Thread-based
  • State machine
  • Mixings/hybrid
• Main loop:
  • Open a connection
  • Read the request
  • Process the request (and create the response)
  • Send the response
  • Close the connection

Common Gateway Interface

• Server uses fork() for the executable
  • Pass the connection to the subprocess
  • Programm fills a template by using database information

2nd Generation Framework (MVC)

• Web server executes the controller per request
• Workflow:
  • Pass the request to the controller
  • Parse the URL and the HTTP request to get them as parameters
  • Use these parameters to retrieve the model from the database
  • View component renders the template by using the model
  • Result: HTML
• e.g., Ruby on Rails, Django
• Note: JavaScript is just a resource on server-side

3rd Generation Framework (JS)

• Usually, simple Web servers can be used to serve HTML, CSS and JS files
• Requirements:
  • HTTP GET ist most dominant request type
  • Database operation
• Further communication:
  • Model data (CRUD operations)
  • Access/modification of session data
• Result: Node.js

Node.js

• Concept:
  • Basis: JavaScript Runtime environment (v8)
  • Add events and management structures (handle all requests using the event loop)
  • Add interfaces to the OS (sockets, files, event handling)
  • Provide a useful module system (visibility of code)
• Goal:
  • Single language used on client and server side
• Supports two paradigms:
  • ==Really?==
  • Threads:
    • Requires scheduler
    • Operations are blocking (transparent to waiting)
  • Events:
    • Non-blocking
    • Fine-granular processing of events
• Main loop:
  • Goal: Never wait or block in an event handling routine
  • Non-blocking

Express.js

• Minimal framework for Node.js
• Features:
  • HTTP (also provided by Node.js)
  • Routing
    • Map URLs to functions
    • Routing table
  • Middleware
    • Manage sessions, cookies
    • Security
    • etc.
• Express app:
  • Routing of HTTP requests
  • Rendering of templates (create HTML)
  • Interface to configure the middleware of the pre-processor

Routing

• expressApp.get(urlPath, requestProcessfunction)
• urlPath may contain parameters
• Other methods:
  • get, post, put, delete, all

Request Handling

• e.g., expressApp.get('/users', (request, response) => {...});
• Request object:
  • params: Parameters of the request
  • query: GET-Parameter
  • body: Content
  • get(field): HTTP Header Parameter

Response Handling

• res.write(content): Write content
• res.status(code): Set status code
• res.set(prop, value): Set headers
• res.end(): Finish and send response
• res.send(content): Equivalent to write(content) and end()
• Supports chaining:
  • res.status(code).write(c1).write(c2).end()

Middleware

• Important for flexibility (pre-process the request)
  • e.g., app.all()
• Examples:
  • Check for user authentication
  • Parse/convert request
  • Session management
  • Cookie management
  • Compression
  • Encryption

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Storage Systems

• Requirements
  • High availability (read and write)
  • High scalability
  • Concurrent access (e.g., transaction model)
  • Fault-tolerant (data loss would be critical)
  • Application data should be well-structured
    • e.g., fast access for model data
  • Easy usage
• Systems:
  • Relational databases
  • NoSQL databases

Relational Databases

• Concepts:
  • Relations (tables)
  • Attributes (column)
  • Tuples (rows)
• Database schema: Describe the structure of the database
• Using SQL (descriptive query language)
• Object Relational Mapper
  • Motivation: Relational model and web application do not always fit
  • Idea: Map OO model to relational model
  • Map objects to tuples
  • Map classes to relations
  • ORMs support the creation and evolution
  • e.g., Rails Active Records, SQLAlchemy

NoSQL Database

• Not-only SQL
• Motivation:
  • NoSQL database fits better to the object-/document-based model of current Web applications
• e.g., MongoDB
  • Data model: JSON
  • Expressive query language
  • Supports indexing
  • Scalable + reliable
• Schema-free or not?
  • JSON-objects are flexible (no constraints)
  • Problem:
    • <h1>{{ person.name }}</h1>
    • person.name should be a character string and not too long
  • Ensure schema using validators (integrity constraints)
    • Push consistency-check into the application
    • e.g., Mongoose, Object Definition Language (ODL)