Building Real-Time Messaging System

LearnCube is an online education platform that enables anyone, anywhere to access world-class teachers. It is designed as a virtual classroom with live chat and other real-time collaborations like a whiteboard.

The platform is trusted by top language schools, tutoring companies & corporate trainers like Oxford University Press, Lingoda, and many others.

LearnCube chose AWS as their cloud platform to become more agile, innovative, and efficient. Based on a variety of AWS tools, Romexsoft helped the customer achieve high scalability, reliability, latency, cost and security optimization.

The client’s main infrastructure is running in AWS Cloud. Having positive experience in collaboration with Romexsoft before, LearnCube asked us to come up with a solution that had to meet two major goals: less expenses compared to the existing solution and high reliability. To resolve this issue our company suggested implementing a real-time messaging system based on API Gateway with WebSockets, Lambda, and ElastiCache services.

Amazon API Gateway is a fully managed service that handles APIs at any scale. Also, it supports two-way WebSocket APIs. Such events like WebSocket connect and disconnect are provided out of the box. So, the solution works in the following way:

• WebSocket connection is initiated from the client-side via Vue.js and passed through API Gateway to the written in Node.js AWS Lambda function that stores connection information like connectionId, userId, and classRoomId in the AWS ElastiCache. API Gateway securely keeps the WebSocket connection in its pool.
• The client sends a message through the opened WebSocket connection to API Gateway’s onMessage endpoint. Another AWS Lambda handler gets classRoomId from the payload, gets all stored in ElastiCache connections with this classRoomId, and performs broadcast of message body using AWS.ApiGatewayManagementApi SDK.
• When the client exits the classroom or class is finished the disconnect event is sent to API Gatewaydisconnect endpoint. AWS Lambda handler gets message info and removes it from ElastiCache. API Gateway removes the connection from its pool.

Custom AWS Lambda authorizer is used to initiate WebSocket connections from authenticated users only. AWS ElastiCache has primary and read replicas in different availability zones to support high availability and performance. Also, ElastiCache is located in the VPC in a private subnet. So Lambda handlers are also placed in the VPC and NAT Gateway is set up to provide an external communication for AWS.ApiGatewayManagementApi SDK to broadcast messages. All Lambdas and API Gateway metrics are recorded in AWS CloudWatch logs.

Real-Time Messaging System AWS Architecture Diagram

• Decreased monthly costs for the real-time messaging app almost 3x times which was a sizable monetary value.
• High reliability and guarantee of messages delivery to the end client.
• Solution transparency and observability via CloudWatch logs and dashboards.