This article talks about shared volumes and the preferred mechanism for data persistence using the Docker containers.
- This article covers the following topics:
- Introduction of the Docker volumes.
- Managing volume using Docker CLI commands or Docker API.
- Sharing data between containers and between containers and hosts
- Sharing database files across containers
- And more…
Introduction
Containers are independent of the storage engine and volumes. Let’s discuss briefly on how Docker accomplishes the idea of images and containers. How does the layer organized in storage and keeping them isolated, letting them be stacked on top of each other as layers?
We are in the era of rapid development and faster deployment; we also know how to do a release faster. Now, we will see how to build the application and port it as a micro-services using containers with data persistence.
Before jumping to the demo, let’s understand the available Docker solutions. Let’s talk about sharing data between containers and between containers and hosts.
Docker offers the solution of data externalization and this feature is called volumes. The volumes are like a shared folder or the directory structures of the file system. They’re virtual discs that you can store data in and share them between the containers, and between containers and the host or both. So they have two main varieties of volumes available within Docker.
We’ve got the persistent ones, where we can place the data there, and it will be available to the host. And when the container goes away, the data will be still available. And, another one is ephemeral volumes. They exist as long as the container is using them. But when no container is using them, they evaporate. So they’re ephemeral. They’ll stick around as long as they’re being used but they’re not permanent. These are not part of images. No part of volumes will be included when you download an image and no part of volumes is going to be involved if you upload an image. They’re for your local data, local to this host. So first let’s talk about sharing data between the host and a container.
The underlying file systems manage and determine which bits on the drive are part of which file and it’s up to the kernel with the file-systems to keep track of every file. Now on top of all that, you can take programs, and programs can pretend to be file systems. We call this FUSE file system. For a detailed example, you can refer here.
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data sharing in SQL Server docker containers
