Docker and virtual machines (VMs) are both technologies used for deploying applications in isolated environments. There is an ongoing debate around whether Docker offers better performance than VMs. This article explores the key differences between Docker and VMs and analyzes the performance of each solution.
What is Docker?
Docker is an open platform for developing, shipping, and running applications in containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it as one package.
Unlike VMs, containers do not bundle a full operating system – they only contain the application and its dependencies. This makes them more lightweight than VMs.
What is a virtual machine?
A virtual machine (VM) is an emulation of a computer system. VMs provide a complete system platform with full-fledged operating systems, virtual hardware, storage, and network resources.
VMs offer isolated environments for running applications. The hypervisor allows multiple VMs to run on a single machine. Each VM includes the application, libraries, binaries, and an entire guest operating system needed to run the application.
Docker containers vs virtual machines
Both Docker and VMs provide isolated environments for running applications securely. VMs provide hardware-level isolation by assigning dedicated resources from the host machine. Docker guarantees CPU, memory, block I/O, and network resources via namespaces and cgroups.
VMs incur substantial overhead as they emulate an entire system environment including virtualized hardware, guest OS, storage, drivers, and more. Docker containers directly leverage the host kernel and only contain the application and its dependencies, making them extremely lightweight.
Docker containers only package the application and dependencies compared to the full operating system that needs to boot for a VM. Hence, Docker containers can start almost instantly, while VMs take minutes to start.
The containerized application can only access the contents of its container. Persistent data can be enabled by attaching Docker volumes. VMs regularly occupy tens of GBs per VM even if the actual usage is small.
Multiple studies have shown that Docker containers demonstrate better performance than VMs in several areas:
- Density: Docker allows 3-5x more container instances than VMs on the same infrastructure.
- Boot time: Docker containers start almost instantly while VMs take several minutes to start.
- Memory utilization: Docker containers consumed 50-75% less memory since they don’t need the entire guest OS.
- Storage: The disk footprint of containers is minimized by not needing full OS images.
In summary, Docker containers are optimized to offer faster boot times, greater density, lower overhead, and minimized disk usage compared to VMs.
When are VMs a better choice over Docker?
While containers offer better resource utilization and performance, there are a few cases where VMs might be more suitable:
- Running apps that need different OS environments not shared with host
- Legacy apps designed for a specific OS that can’t be containerized
- Apps that require complete isolation at hardware level
- When regulatory compliance prohibits sharing kernel with host
- Need flexibility of diverse VM environments like multiple VMs with different distros
So while Docker offers faster deployment cycles and efficient use of resources, VMs provide greater isolation and flexibility to emulate heterogeneous environments.
- Docker containers provide faster boot times, greater density, lower overhead than VMs.
- Containers directly use the host kernel instead of emulating virtual hardware.
- VMs offer complete hardware isolation which may be required by some apps.
- VMs can provide the flexibility to run multiple operating systems.
- For most modern applications, Docker would offer better performance over VMs.
Docker containers demonstrate clear performance advantages over virtual machines for running modern applications by minimizing boot times and resource overhead. The fact that containers leverage the host kernel allows them faster start times and lower memory utilization compared to VMs.
However, VMs provide hardware-assisted isolation along with the ability to emulate different operating systems, hardware, and platforms. This flexibility makes them suitable for certain use cases where Docker cannot be used.
For cloud-native applications built using microservices architectures, Docker would generally deliver faster performance and more efficient resource management over VMs. But legacy monoliths may benefit from the hardware isolation guarantees provided by VMs. The choice between Docker and VMs ultimately depends on the specific needs of the application and environment.
Frequently Asked Questions
- Is Docker safer than a virtual machine?
While Docker containers offer application-level isolation, VMs provide complete hardware isolation. So VMs offer slightly greater security, at the expense of speed and performance. Docker also has a few security vulnerabilities when misconfigured.
- Is Docker free?
The Docker platform and products are free to download, install and use. You only pay for enterprise-grade support subscriptions from Docker, Inc. There are also managed Docker services available from cloud providers which incur costs.
- Can Docker completely replace VMs?
For most modern applications using microservice architectures, Docker provides faster deployment cycles and optimizes resource usage. However legacy monolithic apps or those needing different guest OS environments may still require VMs.
- Does Docker require a VM?
No, Docker can run natively on Linux hosts and has a tiny VM to allow it to run on Mac and Windows machines. But it does not require a full-fledged VM to host containers.
- How does networking differ between Docker and VMs?
Docker containers share same host kernel network stack while VMs emulate virtual NICs and switches. Containers can communicate over any ports whereas VMs route via virtual networks and subnets.
- Can multiple Docker containers share a volume?
Yes, Docker containers can share data using volumes which allow attaching shared filesystem directories or files from the host machine into containers.
- Is Docker an hypervisor?
No. Docker is not a hypervisor. It relies on OS-level virtualization capabilities like namespaces and control groups to isolate containers. Hypervisors like KVM and VMware Workstation are used for hardware virtualization.
- Do Docker containers have individual IPs?
Docker containers share the host IP and port namespace. So they can be exposed to outside world on any available port. Technologies like Docker swarm mode have in-built ingress load balancing.
- How do Docker containers compare to serverless platforms?
While containers offer faster boot times and density than VMs, serverless platforms have nano-second scale boot times with no resource overhead. Containers are still preferred for predictable workloads.
- Why is Docker preferred for microservices?
The lightweight and fast nature of Docker containers make them perfect for deploying individual microservices. Automation friendly Docker images also make CI/CD easier.
- What types of applications benefit from Docker?
Any cloud-native applications like web apps, APIs, and microservices built on modern stacks benefit from using Docker containers and orchestrators like Kubernetes.
- Does Docker work with any language?
Yes. Docker can deploy applications written in any language or framework as it only cares about dependencies and libraries rather than application code.
- Is Docker the best containerization platform?
Docker pioneered containers and remains the most popular container platform. But Kubernetes has become the de facto orchestration layer with support from all vendors.
- How do you monitor Docker in production?
Docker provides native monitoring capabilities. There are also managed solutions that gather Docker metrics, aggregate logs, monitor app health, and provide visual dashboards.
- What are the disadvantages of using Docker?
Added complexity, vulnerabilities if not properly secured, maintaining many images, networking limitations, storage management are some downsides of Docker.
- How does Kubernetes relate to Docker?
Docker provides containers to package applications. Kubernetes manages containerized applications across clusters and handles scaling, failovers, scheduling via its orchestration capabilities.
- Do I need to rebuild images to update Docker containers?
If the app code changes, the Docker image needs to be rebuilt for the changes to reflect. For config changes, containers can be redeployed from existing images without rebuild.
- Is Docker Hub more popular than private registries?
Public registries like Docker Hub host millions of public images. But most enterprises maintain internal registries to store proprietary images with controls around security, compliance and governance.
- How do I control storage with Docker containers?
Docker storage can be managed by adding disk space limits, setting usage quotas, mounting external volumes, configuring thin provisioning in storage drivers, and using specialized Docker storage solutions.
- What are the security risks with Docker containers?
Risks like vulnerable images, insider threats, elevating privileges, poisoning caches, insecure registries, secrets exposure can happen if proper security measures are not implemented while using containers.