Using Docker Volumes for persistent storage in C++ projects

01 Oct 2023

When working with C++ projects, it is crucial to have a mechanism for persistent storage, especially when running your application in a Docker container. Docker volumes provide a practical solution for managing persistent data while keeping your containers stateless and portable.

What are Docker Volumes?

Docker volumes are a way to persistently store data generated by containers. They provide a means to share and manage data between a container and the host or other containers. Volumes can be easily mounted and unmounted, allowing for flexibility and convenience when dealing with data storage in Docker.

Why Use Docker Volumes in C++ Projects?

In C++ projects, there are often requirements to store and access data files, databases, logs, and other artifacts generated during runtime. By utilizing Docker volumes, you can ensure that your data remains intact even if containers are stopped, restarted, or migrated to different environments.

Implementing Docker Volumes in C++ Projects

To use Docker volumes in your C++ projects, follow these steps:

Create a Volume: Start by creating a volume on your Docker host. You can do this by running the following command:
```
$ docker volume create my_data_volume
```
This will create a new volume named my_data_volume.
Mount the Volume: In your Dockerfile or Docker Compose file, add a VOLUME instruction to specify which directory inside the container should be mounted with the volume. For example:
```
# Dockerfile
...
VOLUME /app/data
...
```
This will mount the /app/data directory inside the container with the volume.

Access the Volume: In your C++ code, you can access the mounted volume like any other directory. For example:

// main.cpp
#include <iostream>
#include <fstream>
   
int main() {
    std::ofstream file("/app/data/my_file.txt");
    if (file.is_open()) {
        file << "Hello, Docker volumes!";
        file.close();
        std::cout << "Data written to file." << std::endl;
    } else {
        std::cerr << "Failed to open file." << std::endl;
        return 1;
    }
   
    return 0;
}

In this example, we create a file named my_file.txt inside the mounted volume directory /app/data and write some data to it.

Build and Run the Container: Build and run your container, ensuring that you mount the volume with the appropriate flag:
```
$ docker build -t my_cpp_app .
   
$ docker run -v my_data_volume:/app/data my_cpp_app
```
The -v flag instructs Docker to mount the my_data_volume volume to the /app/data directory inside the container.

Conclusion

By utilizing Docker volumes in your C++ projects, you can ensure persistent storage of your application’s data. This technique allows your containers to be portable and stateless while maintaining access to important files and artifacts. With the ability to easily mount and unmount volumes, Docker provides a flexible solution for managing persistent storage in your C++ applications.

#docker #cpp #devops