How to Run a Command Once in Docker Compose for Data-Dependent Processes?

Susan Sarandon
Release: 2024-11-10 01:19:02
Original
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How to Run a Command Once in Docker Compose for Data-Dependent Processes?

Running a Command Once in Docker Compose

Introduction

Docker compose allows you to manage multiple containers as a single unit. However, it can be challenging to execute commands only once, especially when dealing with data-dependent processes like setting up databases.

Understanding Data Volume Containers

In your compose file, you've created a "mongodata" data volume container to store the MongoDB data. This container is essentially a paused container that simply mounts the assigned volume.

Avoiding Repeated Command Execution

Entrypoint Script for One-Time Initialization:

To prevent the "-setup" command from executing multiple times, you can employ an entrypoint script within the "my_project" container. This script will check if the database has been initialized and perform the setup only if necessary.

Example:

#!/bin/sh

# Check if database is initialized
if test -f /app/initialized; then
  # Database already initialized, skip setup
  echo "Database already initialized"
else
  # Initialize database
  ./my-project -setup
  touch /app/initialized
fi

# Start the application
exec /go/bin/my_project
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Utilizing Volume Management

Docker 1.9 and later provide native volume management capabilities, eliminating the need for "data-only" containers. You can simplify your compose file as follows:

services:
  mongo:
    image: mongo:latest
    volumes:
      - mongodata:/data/db
    ports:
      - "28001:27017"
    command: --smallfiles --rest --auth
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Note on Entrypoint Script

In the entrypoint script, it's essential to handle potential delays in database availability. The script should retry connection attempts if the database is not yet accessible.

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