discord-bot-cdk-construct

A CDK Construct for creating a serverless Discord bot. All you need to do is supply your code to handle the commands!

Architecture Overview

This is the architecture for how this project is laid out server-side. The tools used to create these diagrams are:

Architecture Diagrams

The bot has a fairly straightforward setup:

The biggest confusion likely stems from the use of two Lambda functions instead of one. This is to ensure that the initial request can respond within Discord's 3 second time limit and return a proper response to the user.

Sample Usage

The usage is split into two parts: The AWS CDK stack that will be used, and a "commands" script that actually handles responding. It's recommended that you are familiar with CDK first before diving into using this.

Handling Commands

For handling commands, you just need to provide a Lambda function for sending response to Discord's Web APIs. As an example of how this can be done:

import axios from 'axios';
import {Context, Callback} from 'aws-lambda';
import { DiscordEventRequest, DiscordResponseData, getDiscordSecrets} from 'discord-bot-cdk-construct';

export async function handler(event: DiscordEventRequest, context: Context,
  callback: Callback): Promise<string> {
  const response = {
    tts: false,
    content: 'Hello world!',
    embeds: [],
    allowed_mentions: [],
  };
  if (event.jsonBody.token && await sendResponse(response, event.jsonBody.token)) {
    console.log('Responded successfully!');
  } else {
    console.log('Failed to send response!');
  }
  return '200';
}

async function sendResponse(response: DiscordResponseData,
  interactionToken: string): Promise<boolean> {
  const discordSecret = await getDiscordSecrets();
  const authConfig = {
    headers: {
      'Authorization': `Bot ${discordSecret?.authToken}`
    }
  };

  try {
    let url = `https://discord.com/api/v8/webhooks/${discordSecret?.clientId}/${interactionToken}`;
    return (await axios.post(url, response, authConfig)).status == 200;
  } catch (exception) {
    console.log(`There was an error posting a response: ${exception}`);
    return false;
  }
}

Using the Construct

To create a stack to make use of the above script, you can create a stack like so:

import {Runtime} from '@aws-cdk/aws-lambda';
import {NodejsFunction} from '@aws-cdk/aws-lambda-nodejs';
import {Construct, Duration, Stack} from '@aws-cdk/core';
import * as path from 'path';
import {DiscordBotConstruct} from 'discord-bot-cdk-construct';

/**
 * Creates a sample Discord bot endpoint that can be used.
 */
export class SampleDiscordBotStack extends Stack {
  /**
   * The constructor for building the stack.
   * @param {Construct} scope The Construct scope to create the stack in.
   * @param {string} id The ID of the stack to use.
   */
  constructor(scope: Construct, id: string) {
    super(scope, id);

    // Create the Commands Lambda.
    const discordCommandsLambda = new NodejsFunction(this, 'discord-commands-lambda', {
      runtime: Runtime.NODEJS_14_X,
      entry: path.join(__dirname, '../functions/DiscordCommands.ts'),
      handler: 'handler',
      timeout: Duration.seconds(60),
    });

    const discordBot = new DiscordBotConstruct(this, 'discord-bot-endpoint', {
      commandsLambdaFunction: discordCommandsLambda,
    });
  }
}

This can of course then be used in your CDK application like so:

import { App } from '@aws-cdk/core';
import { SampleDiscordBotStack } from './stacks/sample-discord-bot-stack';

const app = new App();
const startAPIStack = new SampleDiscordBotStack(app, 'SampleDiscordBotStack');

Full Demo Project

A full example project utilzing this construct can be found here. Specifically, the start-api-stack.ts file uses the construct, with DiscordCommands.ts being the commands file (like shown above).

Useful commands

npm run build compile typescript to js
npm run watch watch for changes and compile
npm run test perform the jest unit tests
npm run lint perform a lint check across the code
npm run fix-lint fix any lint issues automatically where possible
cdk deploy deploy this stack to your default AWS account/region
cdk diff compare deployed stack with current state
cdk synth emits the synthesized CloudFormation template

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