Docker vs. virtual machines: What’s the difference?

Here’s a short examination of Docker’s advantages:

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  Portability. Docker’s container technology enables applications to run in different environments: a developer’s personal computer, testing platforms, or cloud providers. Portability ensures that the application is unaffected by system differences without requiring additional configuration.
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  Scalability. Developers can scale applications up or down by dynamically arranging containers. Scalability allows a seamless response to different variations and enables efficient processes.
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  Consistency. Docker containers ensure that the application behaves consistently in different environments and across stages of development, testing, and production. It eliminates the risk of variations leading to unexpected system behavior.
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  Efficiency. Docker containers are lightweight and require fewer system resources, allowing for rapid startup and shutdown, which ensures progressive development and deployment processes.

As convenient as the Docker container mechanism is, it has its drawbacks:

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  Complexity. Docker may be complex to comprehend and configure for those unfamiliar with containerization. It takes some technical knowledge to create Docker files, manage container images, handle networking, and arrange containers.
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  Security. Any misconfiguration of the containers may potentially expose the system to security risks. Although there are ways to enhance Docker’s safety, it requires expertise and careful attention to detail.
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  Performance. While Docker containers are usually more efficient than regular virtual machines, they may not be optimal for resource-intensive applications requiring high performance and low latency, as resources are shared with the host system.
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  Compatibility. Containerization may not be suitable for legacy applications or those relying on specific kernel features. What’s more, Docker primarily runs on Linux, and even though there are Docker adaptations for Windows and macOS, some features might differ depending on the operating system (OS).

A virtual machine (VM) is software that emulates the functionality of a physical server. It performs on your host machine and lets you use a different operating system without affecting your computer’s central system. It is used for tasks like software testing and keeps the processes independent. Numerous virtual machines can coexist on the same hardware, each isolated and secured from one another.

Let’s skim through the advantages of virtual machines:

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  Versatility. VMs can run multiple operating systems on a single physical machine. This allows organizations to use various software requiring different OS environments without a separate physical machine. Versatile VM features allow more flexible use of applications.
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  Cost reduction. VMs can host multiple virtual systems on a single physical machine, reducing the need for additional hardware and helping save equipment, energy, and maintenance costs.
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  Security. Using segregated systems increases their cybersecurity and minimizes the risk of unauthorized access or interference. If one of the virtual machines gets hacked or infected with malware, others hosted on the same hardware will not get affected.
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  Scalability and flexibility. This flexible mechanism allows you to add and remove virtual machines easily. It helps organizations to adapt their infrastructure to changing workloads, business requirements, and demands without substantial manual intervention.

Now that you’re aware of the virtual machine advantages, let’s discuss the drawbacks that this mechanism carries:

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  Limited processing power. Virtual machines rely on the underlying hardware for processing power, meaning there might be efficiency constraints, especially when running resource-demanding applications.
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  Stability issues. Running multiple virtual machines on a single computer might raise stability issues because the guest operating system doesn’t have its own storage, memory, or processing power. If one VM encounters a problem, other machines may experience slowdowns or failures.
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  Limited speed. Application performance on a virtual machine will usually be slower than the same processes run on a host operating system.
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  Host hardware dependency. Because VMs are entirely dependent on the underlying hardware, any failure in the host computer directly impacts the performance of the VMs. Virtual machine and host machine dependency need careful hardware selection and maintenance to prevent such issues.

The table below provides key differences between Docker engine and virtual machine technologies. Remember — your choice between the two depends on your specific needs and intended use cases.

Virtualization

Docker engine uses a containerization technology, where the application and its operational components are packed into a container in the host operating system kernel, virtualizing only the application layer. However, Docker may not be as safe as full virtualization.

Each virtual machine on a computer works entirely independently and fully virtualizes the operating system kernel and the application. VMs provide strong isolation and security but consume more system resources and may not be compatible with resource-demanding applications. This includes scenarios such as desktop virtualization, where VMs can run entire desktop environments.

Compatibility

Virtual machines are more flexible than Docker because they can host almost any application or operating system, providing an environment of physical hardware.

Docker, on the other hand, is oriented towards more modern applications and is fully compatible with Linux applications. You may face compatibility issues if you run Docker on Windows or an older version of Mac.

Replicability

Docker containers are easily duplicated and adapted to various environments. Cloning VMs, however, may be a little more complex and time-consuming due to their larger size and sophisticated configuration.

Size

Docker containers are lightweight and require minimal storage space because they only contain the application and its parameters, not the entire operating system. They’re perfect for environments where space is limited.

Virtual machines containing an entire operating system require larger disk space. They may not be an option for limited storage scenarios.

Security

Because Docker containers depend on the host operating system, they demand careful security practices. If the host OS gets infected with malware, Docker containers may also be exposed to cyber threats. Docker requires regular updates and more advanced monitoring to keep the system safe.

Virtual machines, on the flip side, run their own operating systems, which enhances system security significantly. The isolated virtual environment minimizes the risk of unauthorized access and provides more control over sensitive applications.

Portability

Docker containers ensure the seamless operation of multiple applications across different environments, whether a developer’s laptop, a testing server, or a cloud. VMs, however, deploy applications depending on the host system. This may cause inconsistencies across different environments, which requires advanced management to ensure smooth and continuous behavior.

Performance

The lightweight nature of Docker offers efficient performance because it does not require a separate operating system. However, you might sometimes need to tune and optimize Docker to run resource-intensive tasks or applications.

Virtual machines mimic a standalone computer with an operating system, so they may require more resources to run applications, resulting in lower operational speeds. Optimizing a virtual machine may require careful resource allocation, configurations, and monitoring.

Speed

One of Docker’s main advantages is its fast startup and shutdown times, speeding up deployment processes. While Docker offers lightning speeds, virtual machines usually take longer to load and run an entire operating system. VMs’ slower speeds may impact agility in dynamic environments that need scaling and reconfiguration.

Isolation

Docker creates isolation by packing applications in multiple containers sharing a single OS kernel. Containers must be configured correctly to avoid cross-container interactions or vulnerabilities.

Meanwhile, virtual machines offer complete isolation by segregating each VM on a host computer. Such isolation prevents interference between different virtual machines and provides more system security.

Architecture

Docker’s lightweight and modular design suits microservices and cloud-native applications perfectly. VMs, on the flip side, are more compatible with monolithic or legacy applications, which need a specific structure.

Docker and virtual machines are usually compared by their differences, but they have similarities that define these technologies’ role in seamless organizational system development:

• Resource isolation. Both Docker and virtual machines segregate applications from each other to prevent unauthorized access and interference between different virtual entities.
• Automation and management tools. Both Docker and VMs offer various tools to automate, arrange, and manage applications, which makes it easier to maintain complex environments.
• Cross-platform support. Major operating systems and various other platforms support virtual machines and Docker, showing these technologies’ flexibility and integration with existing infrastructure.
• Deployment consistency. Both Docker and virtual machines allow developers to build and test in environments that are as close to real-life production as possible. Such consistency may ensure an application works similarly in the development and production stages.

These similarities show that the core of these technologies is to provide a framework for organizations to deploy and run applications.

The choice between Docker and virtual machine depends on the specific needs of your project. The most common use cases of these technologies include:

• Docker. Choose Docker for modern, cloud-native applications or microservices. Organizations usually choose Docker for software and application testing and tasks that require enterprise-grade security. Its lightweight design makes it a good choice for scalable environments that rely on CI/DC practices.
• Virtual machines. Choose virtual machines to run legacy or specialized applications that require an environment as close to physical hardware as possible. Use them for tasks that require strong isolation and enhanced security. They are an ideal production environment running on a separate operating system.

In conclusion, virtual machines are usually used for applications that are more or less static, while Docker is used for more dynamic tasks and promotes flexibility. Even though Docker is an emerging technology, we cannot say that organizations stick to it solely. Docker and virtual machines are commonly used in parallel – one is the better choice in some cases than the other.