How to connect to a MySQL Docker container from another Docker container on the same host

Other Questions MySQL
1

Issues with MySQL Connection Between Docker Instances

I’ve set up a MySQL database using Docker with the following commands:

docker network create -d bridge mynetwork
docker run -p 3306:3306 --network mynetwork --name mysql -e MYSQL_ROOT_PASSWORD=5895 -d mysql:latest

I am attempting to connect to this MySQL instance using a Python script. The connection code is as follows:

host='127.0.0.1'
port=3306
user='root'
password='5895'

mysql.connector.connect(
    host=host,
    port=port,
    user=user,
    password=password,
    database=your_database_name
)

This connection works when I execute the Python script locally; however, I want to run this script inside another Docker container.

Dockerfile for the Python Application

FROM python:3.8

WORKDIR /twitter-alpha

COPY requirements.txt .
RUN pip install -r requirements.txt

COPY /constants ./constants
COPY /connectors ./connectors
COPY backfillFollowed.py .
COPY backfillUsers.py .
COPY .env .

RUN apt-get update
RUN apt-get -y install vim

When I build my Docker image using:

docker build -t twitter-alpha . --no-cache

And then run it with:

docker run -itd -p 3000:3000 --name test --network mynetwork twitter-alpha

I encounter the following error:

mysql.connector.errors.DatabaseError: 2003 (HY000): Can't connect to MySQL server on 'localhost:3306' (99)

I discovered that replacing 127.0.0.1 with the container’s IP address obtained from:

docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container_id

fixes the issue, but I’m concerned about relying on the changing IP address each time the container is restarted. What’s the best practice for maintaining a reliable connection?

2

Docker Compose is way better than creating containers manually. It handles all the networking automatically - no more headaches with IPs or manual network setup. Just define both services in your compose file and they can talk to each other using service names directly. I switched to this after hitting the same connection problems you’re having. It’s so much cleaner - your MySQL service is just available at whatever name you give it in the compose file. Plus you can spin up everything with one command and don’t have to worry about container management.

3

Use the container name as your hostname instead of IP addresses or localhost. Since both containers are on the same custom network (mynetwork), Docker’s DNS will automatically resolve the container name to the right IP.

Change your Python connection to:

host='mysql'  # Use container name instead of 127.0.0.1
port=3306
user='root'
password='5895'

This fixes your IP dependency problem. Docker networks handle service discovery automatically - ‘mysql’ will always find your MySQL container even when IPs change. I’ve used this setup in tons of multi-container apps and it works reliably through restarts and deployments. Just keep both containers on the same network and you’re good.

4

Quick fix - don’t use localhost or 127.0.0.1 in your Python container since that just points to the container itself. Use the MySQL container name instead, but also make sure MySQL is actually ready before your app tries to connect. Python often starts faster than MySQL finishes initializing, which causes random connection errors.