Virtual Machines (VMs) and Docker containers are two of the most popular virtualization technologies used today. Both allow multiple virtual environments to run on a single physical server, providing greater efficiency and scalability.
However, there are some key differences between VMs and Docker that make VMs better suited than containers for many use cases:
Greater Isolation and Security
VMs provide stronger isolation and security boundaries between virtual environments than containers. Each VM runs its own full-fledged operating system, while containers share the host operating system kernel.
This means if one container is compromised, there is a higher risk it could access data from other containers or the underlying host. With VMs, breaching one virtual machine does not provide access to other VMs or the host server.
The additional isolation makes VMs preferable for multi-tenant environments, public cloud infrastructure, and any application handling sensitive data.
VMs can run a variety of mainstream operating systems like Windows, Linux, BSD etc. Containers have more limited OS support, mostly Linux based distributions and Windows (with some additional requirements).
This wider cross-platform support allows VMs to run legacy apps or apps built for non-Linux operating systems. Migrating these apps to containers would require significant effort re-architecting and re-platforming the application.
Provisioning a VM allows extensive customization and tuning – choosing VM capacity, cores, storage etc. based on the workload needs.
Containers have more standardized sizing since they share the underlying host OS kernel and resources. While some tuning is possible with containers, VMs provide finer grained control.
Mature Tooling and Ecosystem
As a more mature technology, VMs have an extensive ecosystem of management tools offering features like migration, high availability, monitoring etc.
Docker is catching up in terms of features, but still has gaps in areas like Windows support, bootstorm load testing etc. This makes VMs easier to manage at scale across on-premise and multi-cloud environments.
When are Containers Better Suited?
However, containers do have benefits in certain situations compared to VMs:
- Faster startup times: Containers have faster launch times given their lower overhead
- Efficiency: They make better use of resources when running large numbers of simple apps (like microservices)
- Dev and CI/CD: The lightweight nature works very well for continuous integration and development workflows
So in summary, while containers are catching up, VMs still provide superior security, compatibility, customization and tools support for production workloads at scale. Containers have advantages for simpler stateless applications and developer workflows.
- VMs provide stronger isolation between environments than containers, making them more secure
- They support a wider range of operating systems and allow running legacy apps
- Provisioning VMs allows for more customization of resources and tuning
- Mature VM management tools offer better support for scalability, migration etc.
- Containers have advantages for simpler apps due to faster startup times and efficiency
VMs and containers both have their merits, but in most cases, VMs are still better suited for enterprise production workloads while containers fit simpler cloud native applications.
The additional security, broad OS support, customizable resources and ecosystem tooling give VMs an edge for most real-world line-of-business applications today. As container technology evolves, this may change in the future. But currently VMs provide critical advantages that make them superior to containers in many situations.
- What is a virtual machine (VM)?
A virtual machine is an emulation of a computer system running its own operating system (OS). VMs run on top of a hypervisor, which creates and manages the virtual environment.
- What is a Docker container?
Docker containers allow applications to run in isolated user-space instances called containers. Multiple containers run on a single host sharing the OS kernel but are isolated from each other.
- Why are VMs more secure than containers?
VMs provide stronger isolation between environments and added attack surface than containers. Breaching one VM does not allow access to other VMs or host, reducing security risks.
- Can I run Windows apps on Docker?
Docker has limited Windows support only with recent Windows Server versions and Windows 10. Many legacy Windows apps need re-architecting to run on Docker containers.
- How customizable are resources for VMs vs containers?
VMs allow extensive customization of cores, memory, storage etc. for each workload. Containers have more standardized resource allocation since they share the host kernel.
- Can I live migrate VM workloads across servers?
Yes, mature VM tools like vMotion allow live migration of VM instances across physical servers with near-zero downtime. Similar capabilities for containers are still evolving.
- What VM tools support multi-cloud management?
Tools like VMware vRealize Suite, Microsoft Azure Arc and Google Anthos support managing VMs across on-premise and public cloud environments.
- Why are containers preferred for microservices?
The lightweight nature and fast launch times of containers make them well suited for deploying microservices that follow modern architectural patterns.
- How much faster is Docker container launch time?
Containers have near instant launch times while VMs can take several minutes to start due to the bootup time of a full operating system.
- Why are containers preferred for CI/CD pipelines?
Containers provide standardized environments that can be rebuilt quickly as code moves through the development delivery pipeline enabling faster iterations.
- Do I need to re-architect apps to run on Docker?
In most cases, legacy and monolithic applications designed for VMs need significant refactoring to run well in containers employed for microservices.
- Is Docker enterprise-ready?
Docker is rapidly evolving with enterprise capabilities but still lacks VM support for areas like Windows compatibility, scaling, availability etc.
- How are Docker security capabilities compared to VMs?
Docker has made significant strides, but VMs still provide superior isolation and attack surface reduction between workloads making them more secure.
- What are alternatives to Docker for containerization?
Some alternatives to Docker for containerization include Podman, Containerd, LXC/LXD, Mesos Containerizer, and other open-source projects.
- Can multiple VMs communicate quickly like containers?
Yes, VMs connected to the same hypervisor have access to high-speed communication channels for inter-VM networking enabling low-latency connectivity.
- Which is better for public cloud infrastructure – VMs or Docker?
The additional isolation and security of VMs make them generally a better choice than containers for multi-tenant public cloud environments.