A Docker container is a lightweight, standalone, and executable package that includes everything needed to run a piece of software, including the code, a runtime, system tools, libraries, and settings. Containers are isolated from each other and from the host system, but they share the host system’s kernel.
A virtual machine, on the other hand, is a software implementation of a physical computer that provides a separate operating system and resources. Each virtual machine has its own kernel and runs its own operating system, which means that multiple virtual machines can run on the same host system and be isolated from each other. Virtual machines require more system resources than containers.
There are several reasons why you might choose to use a Docker container instead of a virtual machine.
- Lightweight and efficient: Because containers share the host system’s kernel and do not require a separate operating system, they are more lightweight and efficient than virtual machines.
- Portability: Containers can be easily moved between different environments, such as between a developer’s local machine and a test or production environment.
- Consistency: Containers provide a consistent environment for running software, which can help reduce issues caused by differences in the underlying system.
- Scalability: Containers are easy to scale up or down, making them well-suited for use in microservices architectures and other distributed systems.
- Cost-effective: Because containers use fewer system resources than virtual machines, they can be a more cost-effective solution for running multiple applications on a single host.
Conversely, there are also several good reasons to use a virtual machine instead of a Docker container.
- Isolation: Virtual machines provide a higher level of isolation between the guest operating system and the host system, as each virtual machine has its own kernel and runs its own operating system.
- Security: Virtual machines can provide an additional layer of security by isolating applications and data from the host system and other virtual machines.
- Hardware access: Some applications require direct access to the host system’s hardware, such as GPU or specialized network card, which may not be possible or may have limitations with containers.
- Compliance: Some regulatory compliance or industry standards require the use of virtual machines for certain types of applications or data.
- Legacy support: Some older software may not be compatible with the containerization technology and therefore may require a virtual machine to run.
Note that, the choice between using a container or a virtual machine depends on the use case and the requirements of the specific application. In some cases, a combination of both technologies might be the best solution.
In summary, a container is lightweight and shares the host system’s kernel, while a virtual machine is heavier and has its own kernel.