A container is a light package that contains an application's code and all the libraries and other dependencies the code needs to run. The purpose of containers is to enable developers and systems administrators to deploy applications quickly. Containers help avoid conflicts and other dependency issues that can be troublesome to debug.
You may hear a lot about containerization, especially in the world of app development and microservices. Containerization refers to developers bundling applications into containers, making it easier for users to deploy them. Containers are easy to use and are particularly useful for deploying applications to the cloud because the container doesn't need to care about the configuration of the underlying machine.
What's the Difference Between Containers and Virtual Machines (VMs)?
Simply put, a container is a package that consists of everything you need to run an application in a given environment. The primary difference between a container and a VM is what's included in each package.
A container holds an application and any libraries the application depends upon. It runs on top of an operating system. In contrast, a virtual machine holds an entire operating system and runs on top of a hypervisor. Containers are very lightweight, but they can't communicate with the underlying hardware and are only able to run applications supported by the underlying OS. Virtual machines have greater access to the host machine's hardware, and it's possible to run any operating system supported by that hardware as a VM.
The downside of virtual machines is that they require more resources. Instead of simply loading the binaries that are required for the desired application, they load the entire operating system.
Benefits of Containers
Using containers offers several potential benefits over VMs and deploying applications directly onto the host operating system.
Agility: Rather than having to share instructions for how to install any dependencies and troubleshoot conflicts with other applications on the system, developers can simply share a container that's set up to just work. Anyone running a compatible operating system with adequate hardware can download and run that container and have a working version of the application.
Portability: Because containers don't care about the configuration of the underlying operating system, they can run anywhere. A developer can test an application that requires a specific server configuration without having to worry about whether differences in their development environment might cause problems.
Scalability: Containers are particularly useful for applications being developed with a microservices architecture. Developers can configure individual services to be run as containers, and these containers can be deployed and managed using tools such as Kubernetes. Spinning up extra containers for services that are in high demand and shutting them down when they're no longer needed is an efficient way of scaling web applications, especially compared to simply over-provisioning hardware for a monolithic application.
Resiliency: When applications are running in containers, they're isolated from the remainder of the operating system. Containers may be able to communicate with each other via networking and APIs, but they're running in their own separate environments. If an application running in a container crashes, it shouldn't have an impact on other containers. In addition, container management systems can be used to shut down and restart containers as required, keeping applications running smoothly.
Types of Containers
There are many types of virtualization. When most people talk about containers, they're referring to application virtualization. With this type of virtualization, the application inside the container is tricked into thinking it's interacting directly with the operating system when it's really communicating with a container engine or virtualization layer.
Application virtualization offers a layer of abstraction that allows applications to run on an operating system they weren't designed for. It can also run applications with incompatible dependencies, since each application can be given access to the libraries they need without conflicting with the other application.
In addition to application virtualization, containers can use operating system-level virtualization. Examples of operating system-level virtualization include OpenVZ, Solaris Containers, chroot jails and LXC. Docker containers can also be thought of as an example of OS-level virtualization. With this type of virtualization, the kernel allows the existence of multiple user space instances, which are isolated from each other. Chroot jails are often used in this way as a security measure. OpenVZ is often used to deploy virtual private servers, essentially allowing a Linux server to be divided into several smaller servers without the need to run virtual machines that carry additional resource and performance overhead.
Hardware virtualization is more commonly used by virtual machines. With hardware virtualization, it's possible to mirror an entire physical machine. Each guest OS thinks it's talking directly to the underlying hardware when it's actually speaking to a hypervisor, which can be running on the hardware itself or in a host OS. Hypervisors are responsible for resource management and can set limits on how much memory/processor time each VM has access to at any moment.
Use Cases of Containers
Containers are useful for both development and production environments. Their portable nature makes them useful for DevOps and CI/CD use, while their agility and scalability mean they're equally useful in microservices and cloud deployments. Some examples of real-world container use cases include the following.
Using a microservices architecture makes it possible to develop complex applications quickly and scale them effectively. Many large web applications now use a microservices architecture, including some of the most popular services offered by Google. Containers form a key part of microservices. Each service runs as a separate container, managed by a tool such as Kubernetes. Those containers communicate with each other via REST APIs, with an API gateway serving as the middleman to facilitate communication.
DevOps and CI/CD
Containers are a valuable part of any CI/CD workflow. When developers make changes to an application's code and commit those changes, the CI/CD tools can be triggered to update any container images and run tests. This can offer quicker feedback on the changes to the code and ensures the results are more reliable than if the tests were done on a reviewer's own machine, which may have a different environment configuration to the setup used by the developer.
Hybrid/Multi Cloud Environments
Many organizations now have a multicloud environment, using several different cloud services providers. Others use a hybrid cloud setup, with some on-premises and cloud solutions. Managing applications in these environments isn't always easy. Containers offer a practical solution because they contain everything the application needs to run. Instead of spending time setting up servers, installing libraries and managing complex configurations for each cloud server, the work only needs to be done once, and then the container can be deployed to whatever environment is needed.
Application Development and Deployment
Containers are useful for developing and deploying applications. Many developers provide their applications as containers to make it easy for people to test and deploy them. They also offer containers for developers to use for their work. For example, the popular open-source project Nextcloud suggests developers use Docker containers to manage their development environment.
Containerization is not a new type of technology, but it has become more popular in recent years. Software, such as LXC, has been available for Linux for a very long time. However, it was complex to set up, and this barrier to entry meant it was used only by relatively experienced system administrators and developers.
Docker revolutionized containers by making them easy for almost anyone to run and offering tools, such as the Docker Hub, where people could share containers for anyone to download and run.
Docker itself is quite flexible and powerful, but managing large numbers of containers via the command line isn't easy, and managing containers across multiple cloud hosts is even more challenging. Container management solutions, such as Kubernetes, can assist with container management and health monitoring.
Docker is based on the Open Container Initiative, and many other container and container management solutions are available. For example, Podman offers container management features for docker and other OCI-compatible container solutions.
Challenges and Limitations of Containers
While containers are powerful and flexible, there are some challenges and potential issues to consider before deploying container-based solutions.
Resource limitations: While containers are more lightweight than virtual machines, they may still carry some overhead compared to running an application directly on the host. Let's imagine you'd like to run a web app that relies on the LAMP stack on your machine. If you already have a working web server and database engine on your machine, you could deploy it as a virtual host, and it would run on your existing server. If you deploy it as a docker container, you're running an extra copy of Apache, PHP and MySQL/MariaDB. On a small scale, this overhead may not matter, but as you deploy more and more containers, it may become more noticeable.
Hardware access: Docker containers can't access the underlying hardware in the way that virtual machines can. This may not matter if you're running a simple microservice, but it does negate the use of containers for applications where lower-level access is required.
Lack of standardization: There are multiple container engines, and not all comply with OCI standards. This lack of standardization can be problematic for many organizations. While it's easy enough for an IT team to pick one container standard and use that for all their internal containers, if they're working with third-party vendors that have adopted a different standard, it can make it difficult to set up container management solutions.
Security concerns: Containers are not quite as isolated as virtual machines. They offer some isolation compared to running an application on the underlying operating system directly, but there are still some privilege escalation risks. It's important to take the time to secure your docker/other container repositories, take care when giving docker access to the underlying filesystem and ensure you never run containers as root. Following these precautions should mitigate many of the potential issues with containers.
How to Get Started With Veeam
If you use containers in your development/DevOps or application deployments, securing your data is essential. At Veeam, we offer a variety of data backup, restoration and security options for cloud, on-premises and hybrid environments.
Our tools work with a variety of container solutions and are designed to integrate seamlessly with your existing workflow. If you'd like to try them before you buy, take advantage of our free trials. We even offer a community edition of our Kasten K10 solution for Kubernetes, so if you're a smaller organization with five or fewer instances, you can take advantage of this to protect your data.
If you're not sure which solution would best suit your needs or you'd like some assistance setting up our backup and restoration tools, give us a call. Our team would be happy to offer a consultation and help you get started.