Approaches to application architecture 

What is a 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

Component examples

• API
• Data Access Object
• Controller

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

A service is a component that can be deployed independently

• 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

• 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 device 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

• Client-server
• Peer-to-peer
• Three-tier or n-tier
• Microservices

Recap

• Components are reusable, independent, replaceable, extensible;
• encapsulated, and non-context specific
• Component-based architecture is the decomposition of the system into logical independent components
• Services are made of components and components consist of objects.
• Services are deployed independently and can be reused by multiple systems
• SOA is a loosely coupled services that interface with each other via a communication protocol over a network
• Distributed systems:
  • multiple services on different machines
  • appear to the end-user as a single coherent system

Architectural Patterns in Software

Types of architectural patterns

• 2-tier,
• 3-tier,
• Peer-to-peer,
• Event-driven,
• Microservices,
• Model-view-controller,
• Message-broker,
• Blackboard,
• Pipe-filter, Controller-responder

Examples

• 2-tier: Messaging apps
• 3-tier: Web apps
• Event-driven: Ride sharing
• Peer-to-peer: Cryptocurrency
• Microservices: Social media

Combining patterns

Some patterns can be combined in a single system

Example:

• 3-tier with microservices
• Peer-to-peer with event-driven

Some patterns cannot be combined

Example: Peer-to-peer with two-tier

Application Deployment Environments 

Application environments

Include:

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

Pre-production environments

• Development: Project is being actively coded
• QA: QA team tests the application’s components
• Staging: Replicates production environment but not meant for general users

Production environment

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

On-premises deployment

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

Cloud deployment types

• Public: Shared infrastructure over internet and hardware is owned by the provider
• Private: Infrastructure is provisioned for a single organisation
• Hybrid: Some infrastructure provided over the internet and some provisioned by a single organisation

Recap

• Application environments include developmen test/QA, staging, and production
• Production environments must also take into account non-functional requirements like load, security, reliability, and scalability
• Deployment platforms: on-premises, public, private cloud, & hybrid cloud

Production Deployment Components

Firewall

• Monitors traffic between an interior and an exterior network
• Permits or blocks data based on a set of security rules
• Acts as a barrier between networks to block viruses and hackers from accessing the internal network

Load balancers

Purpose:

• distributes traffic
• efficiently amongst multiple servers

Functions:

• Prevents server traffic overload
• Maximises server capabilities and responsiveness
• Ensures no one server is overworked
• Manages concurrent requests fast and reliably

Web and Application Servers

• Servers: Provide services, resources, data, or applications to a client
• Store, process, and manage network data, devices, and systems

Web Servers:

Delivers web pages, files, images, and videos to the client. Responds to HTTP requests from a browser

App Servers:

• Runs the apps and provides the app to the client or the web server
• Stores code that determines how data can be created, stored, or changed

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 controls a database by connecting it to users or other programs
• Database servers control the flow and storage of data

Recap

• Common production environment components include a firewall, a load balancer, web and application servers, proxy servers, and database servers
• A firewall is a security device that monitors traffic between networks
• Load balancers distribute network traffic among servers
• A web server delivers web content
• An app server provides business logic
• A database server stores and controls the flow of data through a DBMS

Complete Recap

• Software architecture functions as a blueprint and represents the importance of a good architectural design. 
• Structured design breaks down a software problem into well-organized smaller solution elements whereas behavioral models describe the behavior of the system without explaining how the system implements the behavior. 
• Developing UML diagrams saves time and money by helping developers quickly get up to speed on a project, plan features in advance of coding, and navigate source code easily. Types of UML diagrams include state transition, interaction, and class diagrams.  
• Objects contain data, and they also have behaviors that prescribe the actions the object can take, whereas classes are blueprints for objects.  
• A service-oriented architecture (SOA) consists of loosely coupled services that interface with each other via a communication protocol over a network. Distributed systems run on multiple services on different machines, but they appear to the end-user as a single coherent system. 
• An architectural pattern is a repeatable solution to an architectural problem. Types of architectural patterns include 2-tier, 3-tier, event-driven, peer-to-peer, and microservices. Two or more patterns can be combined in a single system, but some are mutually exclusive.  
• Application environments include development, testing or QA, staging, and production. Production environments tend to be more complex than pre-production because they must take into account non-functional requirements like load, security, reliability, and scalability.  
• Application environments can be deployed either on-premises on traditional hardware, or on public, private, or hybrid cloud platforms. 
• Common components needed for a production environment include a firewall, a load balancer, web and application servers, proxy servers, and database servers.