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Data Persistence in Docker - Day 43

Welcome back to the day 42 of #90DaysOfDevOps series! In the world of Docker, we've explored running containers, managing them, and even connecting them through networking. Today, we're going to discuss the mystery of data persistence. Data is a precious asset for any application, and Docker offers robust ways to ensure it's kept safe and sound.


Understanding Data Persistence

Why Data Persistence Matters

Docker containers, by default, are ephemeral. This means that once a container stops or is removed, any data it created inside the container is lost. For most applications, this is not ideal. Imagine a database container where you want to keep records even when the container restarts. This is where data persistence comes into play.


Docker Volumes

Docker volumes are the preferred way to handle data persistence. A volume is a specially designated directory on the host system that's managed by Docker. It's where you can store and manage persistent data that needs to be shared across containers.


To create a volume, you can use the docker volume create command:

docker volume create mydata

And then, you can mount this volume into your container:

docker run -d -v mydata:/data my-container

This command tells Docker to create a new container (my-container) and attach the mydata volume to the /data directory inside the container. Now, any data written to /data in the container will be stored persistently in the volume, even if the container is stopped or removed.


Bind Mounts

While volumes are designed for sharing data across containers, bind mounts are used to share data between the host and a container. They essentially link a directory or file on the host machine into a container.


To create a bind mount, you specify the host path and the container path when running the container:

docker run -d -v /host-data:/container-data my-container

This command maps the /host-data directory on the host to the /container-data directory inside the container. Any data in this directory is accessible from both the host and the container.


Best Practices for Data Persistence

  • Use Volumes for Application Data: When your application needs to store data that should persist across container restarts or be shared between containers, use volumes.

  • Use Bind Mounts for Development: When you're developing or debugging applications and need quick access to source code or logs, bind mounts can be handy.

  • Label and Document Your Volumes: To keep your Docker environment organized, consider labeling your volumes and documenting their purpose.

  • Backup Your Volumes: Just as you would back up any important data, don't forget to include your Docker volumes in your data backup strategy.

Data persistence is vital in the world of Docker. Volumes and bind mounts are your trusted companions for handling persistent data, whether it's for application data that should endure container restarts or for sharing data between the host and containers.


With these techniques, you can ensure your data stays safe and sound as you continue your Docker and DevOps journey. Stay tuned for more insights and practical knowledge to level up your skills!


Thank you for reading!


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