<p>I recently tried containerizing my FastAPI Python server (also for replication/doubling purposes). Before, I had just a MySQL server in a Docker container and everything was fine, but when I also made my web server a service, it couldn't connect to the MySQL server, so now the application doesn't work.</p> <p>The following is a code snippet for the server database initialization connector in the application</p> <pre class="lang-py prettyprint-override"><code>from fastapi import FastAPI import mysql.connector app = FastAPI() dbconfig = { "host": "localhost", "database": "server_db", "user": "db_user", "password": "user-password" } # Check database connection try: init_cnx = mysql.connector.connect( host='localhost', user='db_user', password='user-password' ) cursor = init_cnx.cursor() cursor.execute("SHOW DATABASES LIKE 'server_db'") if cursor.fetchone() == None: # If the database does not exist, create the database cursor.execute("CREATE DATABASE server_db") cursor.execute("USE server_db") cursor.execute("CREATE TABLE Messages (" "message_id INT NOT NULL AUTO_INCREMENT," "sender_name VARCHAR(32)," "message_text VARCHAR(64)," "created_at DATE," "user_messages_count INT," "PRIMARY KEY (message_id));") print('Database has been created!') cursor.close() init_cnx.close() except mysql.connector.Error as err: print("An error occurred in init_cnx:", err) # Database I/O function async def execute_db_query(query, cursor_buffered=False): cnx = mysql.connector.connect(**dbconfig) try: cursor = cnx.cursor(buffered=cursor_buffered) cursor.execute("USE server_db") cursor.execute(query) result = cursor.fetchall() cnx.commit() print("Query executed successfully!") return result except Exception as e: print("Error while executing query:", e) finally: if cnx: cnx.close() # Get the root directory function, just used to check whether the application is connected to the database @app.get("/") async def get_root(): try: entries_count = await execute_db_query("SELECT COUNT(*) FROM Messages", cursor_buffered=True) return {"Messages entries": entries_count[0][0]} except Exception as e: return {"Error": e} </code></pre> <p>Server’s Dockerfile</p> <pre class="brush:php;toolbar:false;">FROM python:3.11.4-slim-bookworm WORKDIR/app COPY requirements.txt . RUN pip install --no-cache-dir -r requirements.txt COPY server.py . EXPOSE 8000 CMD ["uvicorn", "server:app", "--host", "0.0.0.0", "--port", "8000"]</pre> <p>init.sql script</p> <pre class="lang-sql prettyprint-override"><code>CREATE USER 'db_user'@'%' IDENTIFIED BY 'user-password'; GRANT ALL PRIVILEGES ON *.* TO 'db_user'@'%' WITH GRANT OPTION; FLUSH PRIVILEGES; </code></pre> <p>and docker-compose.yml</p> <pre class="lang-yaml prettyprint-override"><code>version: "3.8" services: db_mysql: image: mysql:8 restart: always environment: MYSQL_ROOT_PASSWORD: "root" volumes: - "./mysql/init.sql:/docker-entrypoint-initdb.d/init.sql" - "./mysql/db_mysql_data:/var/lib/mysql" - "./mysql/mysql_logs:/var/log/mysql" networks: -dummy_network server_1: image: dummy_msg_server ports: - "8081:8000" networks: -dummy_network #command: sh -c "sleep 60s" depends_on: -db_mysql server_2: image: dummy_msg_server ports: - "8082:8000" networks: -dummy_network #command: sh -c "sleep 60s" depends_on: -db_mysql volumes: db_mysql_data: #external: true networks: dummy_network: driver: bridge </code></pre> <p>Although trying to use the API before the MySQL container has been fully initialized may result in an error, this is not a problem because I wait until the MySQL server indicates it is ready to handle the request. Other than that, I'm not trying to connect to the MySQL server. </p> <p>I tried to connect using hostname/IP address. Try changing the python:3.11.4 image in the dockerfile to an earlier debian version and not using the slim image. Try to explicitly use a public network for the container. Docker keeps showing that the container is in a network, and the curl request from the server container returns something. Additionally, docker-compose.yml previously provided port 3306:3306 for the db_mysql service. Guess that's not a problem either. </p> <p><strong>Update 1. </strong>During investigation, it was discovered that if the database has already been created, the application has no problem sending requests to it and getting the correct response.The only problem with it is that the database cannot be created using the create script in the code. </p><p> (Guess, I should update the code block since the project is in another phase now.)</p>

version: "3.8"
services:
  db_mysql:
    image: mysql:8
    restart: always
    ports:
      - 3306:3306
    environment:
      MYSQL_ROOT_PASSWORD: "root"
    volumes:
      - "./mysql/init.sql:/docker-entrypoint-initdb.d/init.sql"
      - "./mysql/db_mysql_data:/var/lib/mysql"
      - "./mysql/mysql_logs:/var/log/mysql"
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-uroot", "-proot"]
      timeout: 1s
      interval: 40s
      retries: 5

  server_1:
    build:
      context: .
      dockerfile: Dockerfile
    restart: always
    ports:
      - "8081:8000"
    depends_on:
      db_mysql:
        condition: service_healthy

  server_2:
    build:
      context: .
      dockerfile: Dockerfile
    restart: always
    ports:
      - "8082:8000"
    depends_on:
      db_mysql:
        condition: service_healthy

volumes:
  db_mysql_data: #external: true