한국어 README.md

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Chat API

Chat API provides chat functionalities. It provides websocket endpoint to retrieve and send messages in real-time and provides REST endpoint to retreive conversations or message history.

Architecture

Architecture Overview Diagram

Architecture Details Diagram

Components

AWS RDS (Postgres)

• We expose AWS RDS via AWS RDS Proxy.
• The schema is defined in user-api.
• The permission for Lambda to access AWS RDS Postgres is set up in lib/chat-api-stack.ts.

AWS Elasticache (Redis)

We use a single REDIS cluster with two fields - chat_user_connection, chat_connection_user.

• chat_user_connection stores { user_id: connection_id } and chat_connection_user stores { connection_id: user_id }. They are used to manage connection ids for each user.

AWS Aurora (PostgreSQL Serverless)

We use serverless Aurora PostgreSQL for easier auto-scaling. It stores all the data related to chat functionalities. The table definition is written db_init.sql.

• conversation_table stores metadata about each conversation.

• participant_table stores the relationship between conversations and their participants. A row is defined as a [conversation, user] pair. Thus, the number of rows for each conversation equals the number of participants in each conversation.

• message_table stores message data. It has conversation_id as an attribute to indicate which conversation the message is part of.

• message_is_read_table stores data of whether a user read a message or not. Its purpose is to indicate whether a user has unread messages or not.

The SQL diagram is as follows.

AWS Lambda Function

It provides all the chat functionalities with serverless framework.

• heartbeat is invoked via websocket every several minutes by Chrome extension background.js. AWS Websocket has idle timeout of 10 minutes, so heartbeat is sent through websocket to keep the connection alive.

• connect is invoked via websocket when a user connects. It sets the user's connection id in chat_user_connection and chat_connection_user Redis fields.

• close_connection is invoked via websocket when a user closes connection. It removes connection information in chat_user_connection and chat_connection_user Redis fields.

• send_message is invoked via websocket when a user sends a message. It saves the new message in message_table and sets the message as read for the sender. Then, it posts the new message to the user's friends who are online via the websocket connection.

• read_messages is invoked via websocket when a user reads a message/conversation. It updates the rows in message_is_read_table.

• get_user_conversations is invoked via REST Api. It returns the user's conversations with additional details (e.g. content of the most recent message, whether the user read the latest message or not, and etc.) obtained via SQL query. This data is displayed in the user conversation list page.

• get_conversation_messages is invoked via REST Api. It returns the messages in a conversation.

• get_conversation_participants is invoked via REST Api. It returns the participants of a conversation.

• get_user_direct_conversation is invoked via REST Api. For a given target user, it returns the conversation id of the one-on-one conversation with the target user. It returns null if the one-on-one conversation does not exist.

• create_conversation is invoked via REST Api. It creates a new conversation.

• get_conversation is invoekd via REST Api. It returns the information of a conversation given as input parameter.

AWS API Gateway

• REST API - Provides endpoint for CRUD operations of conversations.

• Websocket API - Provides websocket connection for Chrome extension background.js to send and retrieve message data.

Setup

Environment Variables

In .env set the following environment variables.

COGNITO_REGION=<AWS region>
COGNITO_POOL_ID=<AWS Cognito User Pool Id>

VPC_ID=<VPC of the backend>
PRIVATE_ROUTE_TABLE1_ID=<Route Table1 id of subnets AWS RDS resides in>
PRIVATE_ROUTE_TABLE2_ID=<Route Table2 id of subnets AWS RDS resides in>
PRIVATE_SUBNET1_ID=<Id of subnet1 AWS RDS resides in>
PRIVATE_SUBNET2_ID=<Id of subnet2 AWS RDS resides in>

SUBNET1_AZ=<Availability zone of subnet1 (e.g. us-west-2a)>
SUBNET2_AZ=<Availability zone of subnet2>

RDS_PROXY_SG_ID=<Security Group of AWS RDS Proxy>
RDS_PROXY_HOST=<AWS RDS Proxy Host>
RDS_PORT=<AWS RDS Port Number>
RDS_DB_NAME=<AWS RDS database name>
RDS_USERNAME=<AWS RDS username>
RDS_PASSWORD=<AWS RDS password>

RDS_PROXY_ARN=<AWS RDS Proxy arn>
RDS_PROXY_NAME=<AWS RDS Proxy name>

LAMBDA_SG_ID=<AWS Lambda Security Group if it exists. 'none' otherwise>
REDIS_SG_ID=<AWS Elasticache Security Group if it exists. 'none' otherwise>
REDIS_ENDPOINT_ADDRESS=<Elasticache primary endpoint host if it exists. 'none' otherwise>
REDIS_ENDPOINT_PORT=<Elasticache primary endpoint port if it exists. 'none' otherwise>

REST_API_DEPLOY_STAGE=prod
WEBSOCKET_API_DEPLOY_DEV_STAGE=dev
WEBSOCKET_API_DEPLOY_PROD_STAGE=prod

CLIENT_URL=<Url of the chat client>

CDK Bootstrap

For initialization, bootstrap AWS CDK by runnin

cdk bootstrap aws://<AWS Account Id>/<AWS Region>

Refer to https://docs.aws.amazon.com/cdk/latest/guide/bootstrapping.html for more details.

Deployment

• Run cdk deploy --outputs-file chat-api.json.
• On AWS console, deploy ChatWebsocketApi Prod API manually since autoDeploy is set to False.

Setting Up the Database

• On the Query Editor of AWS RDS console, copy the content of db_init.sql to the editor and run it.

Tests

Note that tests are not functional right now. They are to be updated soon.