Software Architecture Design and Patterns

Introduction to Software Architecture

Software architecture and design:

Design and documentation take place during the design phase of the SDLC
Software architecture is the organization of the system
Serves as a blueprint for developers
Comprised of fundamentals structures and behaviors

Early design decisions:
How components interact
Operating environment
Design principles
Costly to change once implemented
Addresses non-functional aspects

Why software architecture is important:
Communication
Earliest design decisions
Flexibility
Increases lifespan

Software architecture and tech stacks:
Guides technology stack choice
Tech stacks must address non-functional capabilities
Tech stacks include:
- Software
- Programming languages
- Libs
- Frameworks
- Architects must weigh advantages and disadvantages of tech stack choices

Artifacts

Software design document (SDD)
Architectural diagrams
Unified modeling language (UML) diagrams

Software Design Document (SDD)

Collection of tech specs regarding design implementation
Design considerations:
- Assumptions
- Dependencies
- Constraints
- Requirements
- Objectives
- Methodologies

Architectural diagrams
It displays:

Components
Interactions
Constraints
Confines
Architectural patterns

UML diagrams

Visually communicate structures and behaviors
Not constrained by a programming language

Deployment considerations

Architecture drives production environment choices
Production environment is the infrastructure that runs and delivers the software
- Servers
- Load balancers
- Databases

Software Design and Modeling

Software Design:

Software design is a process to document:

Structural components
Behavioral attributes

Models express software design using:
Diagrams and flowcharts
Unified Modeling Language (UML)

Characteristics of structured design:
Structural elements: modules & submodules
Cohesive
Loosely coupled

Structure diagram example:

Behavioral models:

Describe what a system does but doesn’t explain how it does it
Communicate the behavior of the system
Many types of behavioral UML diagrams
- State transition
- Interaction

Unified Modeling Language (UML):

Visual representations to communicate architecture, design, and implementation
Two types: structural and behavioral
Programming language agnostic

Advantages of Unified Modeling Language (UML):

State transition diagram example:

Interaction diagram:

Object-Oriented Analysis and Design

Object-Oriented Languages:

A patient could be an object
An object contains data, and an object can perform actions

Classes and objects:

Object-Oriented analysis and design:

Used for a system that can be modeled by interacting objects
OOAD allows developers to work on different aspects of the same application at the same time
Visual UML diagrams can be made to show both static structure and dynamic behavior of a system

Class diagram:

Software Architecture Patterns and Deployment Topologies

Approaches to Application Architecture

What is component?

An individual unit of encapsulated functionality
Serves as a part of an application in conjunction with other components

Component characteristics:

Reusable: reused in different applications
Replaceable: easily replaced with another component
Independent: doesn’t have dependencies on other components
Extensible: add behavior without changing other components
Encapsulated: doesn’t expose its specific implementation
Non-context specific: operates in different environments

Components examples:

Component-based architecture:

Decomposes design into logical components
Higher level abstraction than objects
Defines, composes, and implements loosely coupled independent components, so they work together to create an application

Services

Designed to be deployed independently and reused by multiple systems
Solution to a business need
Has one unique, always running instance with whom multiple clients communicate

Examples of Services:

A service is a component that can be deployed independently
Checking a customer’s credit
Calculating a monthly loan payment
Processing a mortgage application

Service-oriented architecture:

Loosely coupled services that communicate over a network
Supports building distributed systems that deliver services to other applications through the communication protocol

Distributed systems

Multiple services located on different machines
Services coordinate interactions via a communication protocol such as HTTP
Appears to the end-user as a single coherent system

Distributed system characteristics:

Shares resources
Fault-tolerant
Multiple activities run concurrently
Scalable
Runs on a variety of computers
Programmed in a variety of languages

Nodes:

Any devices on a network that can recognize, process, and transmit data to other nodes on the network
Distributed systems have multiple interconnected nodes running services

Distributed system architectures:

Architectural Patterns in Software

Types of architectural patterns:

2-tier

3-tier

Peer-to-peer (P2P)

Event-driven

Microservices

Examples:

Combining patterns

Application Deployment Environments

Application environments:

Include:

Application code/executables
Software stack (libs, apps, middleware, OS)
Networking infrastructure
Hardware (compute, memory and storage)

Pre-production environments:

Production environment

Entire solution stack ++
Intended for all users
Take load into consideration
Other non-functional requirements
- Security
- Reliability
- Scalability
More complex than pre-production environments

On-premises deployment:
System and infrastructure reside in-house
Offers greater control of the application
Organization is responsible for everything
Usually more expensive than compared to cloud deployment

Cloud deployment types:

Production Deployment Components

Production deployment infrastructure:

Web and application servers:

Proxy server:

An intermediate server that handles requests between two tiers
Can be used for load balancing, system optimization, caching, as a firewall, obscuring the source of a request, encrypting messages, scanning for malware, and more
Can improve efficiency, privacy, and security

Databases and database servers:
Databases are a collection of related data stored on a computer that can be accessed in various ways
DBMS (Database Management System) controls a database by connecting it to users or other programs
Database servers control the flow and storage of data