How to create a bot that publishes the daily top post of a subreddit to a Discord channel (Docker).

1 - Create a new Dockerfile in your project directory:

FROM python:3.9-slim-buster

WORKDIR /app

COPY requirements.txt .

RUN pip install --no-cache-dir -r requirements.txt

COPY . .

CMD [ "python", "bot.py" ]

This Dockerfile uses the official Python 3.9 image as a base, sets the working directory to /app, copies the requirements.txt file, installs the required packages, copies the rest of the files in the directory, and runs the bot.py script when the container starts.

2 - Create a docker-compose.yml file in your project directory:

version: '3'

services:
  bot:
    build: .
    environment:
      - DISCORD_TOKEN=<your-bot-token>
      - REDDIT_CLIENT_ID=<your-reddit-client-id>
      - REDDIT_CLIENT_SECRET=<your-reddit-client-secret>
      - REDDIT_USER_AGENT=<your-reddit-user-agent>
      - DISCORD_SERVER_ID=<your-discord-server-id>
      - DISCORD_CHANNEL_ID=<your-discord-channel-id>
      - SUBREDDIT=<your-subreddit-name>
    restart: always

3 - Create a requirements.txt file in your project directory with the following contents:

discord.py
praw

This file specifies the required Python packages for the bot to run.

4 - Modify your bot.py script to use environment variables for the bot token, Reddit API credentials, Discord server and channel IDs, and subreddit name, like this:

import os
import discord
import praw
import datetime

# Discord bot token
TOKEN = os.environ["DISCORD_TOKEN"]

# Reddit API credentials
REDDIT_CLIENT_ID = os.environ["REDDIT_CLIENT_ID"]
REDDIT_CLIENT_SECRET = os.environ["REDDIT_CLIENT_SECRET"]
REDDIT_USER_AGENT = os.environ["REDDIT_USER_AGENT"]

reddit = praw.Reddit(
    client_id=REDDIT_CLIENT_ID,
    client_secret=REDDIT_CLIENT_SECRET,
    user_agent=REDDIT_USER_AGENT
)

# Subreddit to retrieve top post from
SUBREDDIT = os.environ["SUBREDDIT"]

# Discord server and channel to post to
SERVER_ID = int(os.environ["DISCORD_SERVER_ID"])
CHANNEL_ID = int(os.environ["DISCORD_CHANNEL_ID"])

# Get today's date in the format "MM/DD/YYYY"
today = datetime.datetime.now().strftime("%m/%d/%Y")

# Get the top post of the day from the subreddit
top_post = reddit.subreddit(SUBREDDIT).top(time_filter="day", limit=1).__next__()

# Build the message to post to Discord
message = f"**Top post on r/{SUBREDDIT} for {today}:**\n\n{top_post.title}\n\n{top_post.url}"

# Authenticate the Discord bot using its token
client = discord.Client()

@client.event
async def on_ready():
    # Get the Discord server and channel to post to
    server = client.get_guild(SERVER_ID)
    channel = server.get_channel(CHANNEL_ID)

    # Post the message to the Discord channel
    await channel.send(message)

# Run the Discord bot
client.run(TOKEN)

5 - Start the Docker

You can then use the docker build . command to build a Docker image from the Dockerfile in your work directory.

You would be able to see your docker images by the below command:

docker images

Without a name, just using the ID:

docker run -i -t 8dbd9e392a96 /bin/bash

Creating a discord bot and getting a token.
How to get client_id and client_secret.
Discord Channel ID