SaaS-25

askmeanything is a project developed by two undergraduate students, Nefeli Myropoulou and Iliana Xigkou for the course SaaS 2021 NTUA ECE.

Purpose

askmeanything gives its users the opportunity to:

• View posted questions
• View the answers to the above questions
• View statistical diagrams regarding the amount of questions/answers posted per day in the last week and the most used keywords in the questions.

After registration, which is free, users obtain even more capabilities. They can:

• View all questions and filter them based on the name of the author, the attached keywords, or date that they were created
• Post their own questions
• Answer posted questions
• View statistical diagrams stated as above based on their activity
• Update the account information

Technology Stack

During the development of this app these technologies are used:

• PostgreSQL as the DBMS.
• Sequelize as the ORM for the communication with the DBMS.
• NodeJS as the JavaScript runtime.
• ExpressJS as the web application framework for the implementation of the services in SOA and Microservices architecture.
• ReactJS as the JavaScript library for the front-end.
• Bootstrap as the tool for the design and customization of the website's front-end.
• Redis as the in-memory key–value database and message broker for the implementation of the Choreographer in the MicroServices architecture.
• PassportJS as an authentication middleware for NodeJS.
• Heroku for the SOA and the Microservices apps' deployment.
• EmailJS as the third-party service for sending emails to users after they have contacted us via the corresponding 'contact us' form.

Architectures

Service-Oriented Architecture (SOA)

The implementation of the app based on SOA is located in the back-end and front-end directories. It was broken down into 3 services containing the following business logic:

• Authenticator service:
  • Register a new user
  • Sign in an existing user
  • Sign out a signed-in user
  • Get the account information of an existing user
  • Update the account information of an existing user
  • Validate the token of a signed-in user
• QnAOperations service:
  • View all questions (*)
  • View the 10 most recent questions (available to not signed-in users instead of the 'view all questions' functionality)
  • Filter questions based on the author, the attached keywords and the posting date (*)
  • View all the questions the signed-in user has posted or contributed to (*)
  • Create a new question (*)
  • View all the answers to an existing question
  • Answer an existing question (*)
• Analytics service:
  • View statistic data regarding the amount of questions posted per day, during the last week
  • View statistic data regarding the amount of answers posted per day, during the last week
  • View statistic data regarding the most used keywords
  • View statistic data regarding the amount of questions posted by the signed-in user per day, during the last week (*)
  • View statistic data regarding the amount of answers posted by the signed-in per day, during the last week (*)
  • View statistic data regarding the most used keywords by the signed-in user (*)

The functionalities noted with an asterisk are only available to signed-in users.

Data access layer

The above services communicate with the Data access layer via its provided interfaces (API) in order to obtain the corresponding data from the database. Thus, this layer is implemented as a different app, the only one with the ability to communicate directly with the database.

Enterprise Service Bus (ESB)

The ESB is implemented as a different app for the inter-service communication and specifically for the user's token validation everytime he wants to access protected resources via a request.

Analytics service ⟷ ESB ⟷ Authenticator service

QnAOperations service ⟷ ESB ⟷ Authenticator service

Microservices architecture

The implementation of the app based on Microservices architecture is located in the back-end-micro and front-end-micro directories. It was broken down into 5 microservices:

• Authenticator service:
  • Register a new user
  • Sign in an existing user
  • Sign out a signed-in user
  • Get the account information of an existing user
  • Update the account information of an existing user
  • Validate the token of a signed-in user
• Question service:
  • Create a new question (*)
• Answer service:
  • View an existing question and all of its answers
  • Answer an existing question (*)
• QnADisplay service:
  • View all questions (*)
  • View the 10 most recent questions (available to not signed-in users instead of the 'view all questions' functionality)
  • Filter questions based on the author, the attached keywords and the posting date (*)
  • View questions which the signed-in user has posted or contributed to (*)
• Statistics service:
  • View statistic data regarding the amount of questions posted per day for the last week
  • View statistic data regarding the amount of answers posted per day for the last week
  • View statistic data regarding the most used keywords
  • View statistic data regarding the amount of questions posted by the signed-in user per day for the last week (*)
  • View statistic data regarding the amount of answers posted by the signed-in per day for the last week (*)
  • View statistic data regarding the most used keywords by the signed-in user (*)

The functionalities noted with an asterisk are only available to signed-in users.

Choreographer

The Choreographer is implemented as a different app responsible for the notification of the appropriate services upon an occurring event (new user creation, new question, or new answer submission). For this purpose, Redis is used with the below configuration:

• 4 keys:
  • bus
    • Field messages, with all the messages that the Choreographer has received
  • publishers:
    • Field channel_users, with the publisher to that channel, i.e. the Authenticator service
    • Field channel_questions, with the publisher to that channel, i.e. the Question service
    • Field channel_answers, with the publisher to that channel, i.e. the Answer service
  • subscribers:
    • Field channel_users, with the subscribers to that channel, i.e. the Question service, Answer service, QnADisplay service and Statistics service
    • Field channel_questions, with the subscribers to that channel, i.e. the Answer service, QnADisplay service and Statistics service
    • Field channel_answers, with the subscribers to that channel, i.e. the QnADisplay service and Statistics service
  • services:
    • Field AuthenticatorService
    • Field QuestionService
    • Field AnswerService
    • Field QnADisplayService
    • Field StatisticsService
      with all the provided capabilities by each service

Moreover, in case a service is down and an amount of messages is created and ignored by this service, it is ensured that once it is functional again, it can obtain the missing messages from the bus messages field.

Deployment

For the deployment of the app askmeanything the cloud application platform Heroku was used.

For the deployment of the app the instructions as stated below are executed given that one has installed the Heroku CLI:

heroku login

heroku create <app-name>

heroku git:remote --app <app-name>

git subtree push --prefix path/to/project heroku main

For the connection of the Heroku Postgres and Heroku Redis these instructions are executed:

• Heroku Postgres:

heroku addons:create heroku-postgresql:hobby-dev

• Heroku Redis:

heroku addons:create heroku-redis:hobby-dev 
heroku addons:attach <app-name-with-redis>::REDIS --app <app-name-to-share-redis>

Documentation

During the development of this app diagrams are created with Visual Paradigm and used as a guide. These diagrams can be found in the VPP project askmeanything-25.vpp in the directory documentation following this structure:

1. Entity Relationship diagram: ER diagram
2. Class diagram: Class Diagram
3. Component diagrams:
   • SOA1
   • SOA2 (more detailed)
   • SOA Front-End
   • Microservices1
   • Microservices2 (more detailed)
   • Microservices Front-End
4. Deployment diagrams:
   • SOA
   • Microservices