How to Keep a Docker Container Running with Docker Compose

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When working with Docker Compose, it’s common to encounter situations where you need a container to stay running indefinitely, especially in development environments or when containers are used for tasks that don’t keep them active, such as hosting databases or running applications that wait for user input. This article explores strategies and solutions for keeping containers running using Docker Compose, ensuring your services remain available as needed.

Table of Contents

Understanding Why Containers Exit

Before diving into solutions, it’s important to understand why containers might exit prematurely. A Docker container runs as long as its main process does. If this process completes or encounters an error, the container will stop. For applications that exit after execution or lightweight services that don’t have a daemon mode, keeping the container running requires a workaround.

Strategy 1: Overriding the Default Command

The simplest approach to keeping a container running is to override its default command with one that does not exit. Using a command that hangs indefinitely can achieve this.

Docker Compose Example: tail -f /dev/null

One common method is to use tail -f /dev/null as the command. This command effectively does nothing but wait indefinitely without consuming significant resources.

version: '3'
services:
  myservice:
    image: myimage
    command: tail -f /dev/null

This method is straightforward and works well for containers where you don’t need to run a specific command at startup but want to keep the container alive for interactive exploration or debugging.

Strategy 2: Using a Dummy Process

For situations where you need the container’s main application to run and the container to stay active when the main process is idle, you can start a dummy process alongside your application.

Docker Compose Example: Using docker-compose.yml with sleep infinity

In the following example, sleep infinity is used to keep the container running indefinitely. This approach is useful when you have an entrypoint script that starts your main process and you also need to prevent the container from exiting.

version: '3'
services:
  myservice:
    image: myimage
    entrypoint: /my-entrypoint.sh
    command: ["sh", "-c", "sleep infinity"]

In this case, /my-entrypoint.sh should start your application in the background before executing sleep infinity.

Strategy 3: Implementing a Healthcheck

Another approach to keep a container running, particularly useful for services that might crash or need to be in a healthy state to be considered “running,” is to implement a healthcheck.

Docker Compose Example: Healthcheck

version: '3'
services:
  myservice:
    image: myimage
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost"]
      interval: 30s
      timeout: 10s
      retries: 3

While the healthcheck itself does not keep the container running, it allows Docker to restart the container if it becomes unhealthy, ensuring the service remains available.

Strategy 4: Using an Init System

For more complex scenarios where you need to manage multiple processes within a single container, using a minimal init system like tini or supervisord can help keep your container running by managing your processes for you.

Docker Compose Example: Using tini

version: '3'
services:
  myservice:
    image: myimage
    entrypoint: ["/usr/bin/tini", "--"]
    command: /start-my-service.sh

Tini acts as a lightweight init system that reaps zombie processes and forwards signals, ensuring your container’s main process is always running.

Conclusion

Keeping Docker containers running requires understanding your application’s behavior and the tools Docker provides. Whether by overriding the default command, using a dummy process, implementing a health check, or managing processes with an init system, Docker Compose offers flexible solutions to meet your needs. By selecting the strategy that best fits your scenario, you can ensure your containers stay up and running as intended.

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Anastasios Antoniadis

Anastasios Antoniadis is the founder and editor-in-chief of BORDERPOLAR... He is a software engineer, blogger, and avid gamer covering tech, gaming, and coding guides for over 4 years. He is a 2014 graduate of the Department of Informatics and Telecommunications of the University of Athens, an M.Sc. holder in Computer Science, and a Ph.D. student in Program Analysis.