A containerized environment is a virtual environment that enables applications to run and operate within isolated spaces known as containers. The core idea behind the container approach is that an application is bundled into a specialized package along with all its dependencies — such as libraries and configuration files — and isolated as much as possible from the host operating system and other processes. This makes it both easy and safe to run the application across different infrastructures. The package that contains everything needed to launch a container is called a container image.
Because the contents of a container are isolated and independent of the system or device configuration, the container can run in any environment and under any operating system. This principle is known as “write once, run anywhere” (WORA). The container approach reduces both software development and testing time and costs, while also increasing system resilience and security — since a failure or vulnerability in one container does not affect the others.
The main difference between containerized environments and virtual machines (VMs) lies in their isolation mechanism. A VM emulates hardware and runs a full guest OS to execute applications. A container, on the other hand, shares the kernel of the operating system it is running on (the host OS), but is logically isolated with the help of kernel mechanisms, such as namespaces and control groups (cgroups) in Linux. This makes containers much lighter in weight: they start up faster and consume fewer resources.
Managing containerized environments
Specialized tools are used to manage containerized environments.
- Container runtimes are software components responsible for launching containers and managing their lifecycle. They can be divided into two types:
- Low-level runtimes: software responsible exclusively for launching containers. Examples include runc and lxc.
- High-level runtimes: software environments for container management, such as Docker and containerd.
- Orchestrators are tools that manage clusters of containers. They automatically deploy and scale containers, while also monitoring and controlling the resources allocated to them on physical devices or in the cloud. A prime example of an orchestrator is Kubernetes.
Security of containerized environments
Several key threats associated with containers can be identified:
- Container escape. Exploiting vulnerabilities in the OS, the runtime, or misconfigured access permissions, can allow an attacker to break out of the isolated environment and gain control over the host machine or other containers.
- Supply chain These involve the compromise of pre-built images in public registries, such as Docker Hub. Running these compromised images can lead to the infection of the entire infrastructure.
- Orchestrator exploitation. Vulnerabilities and configuration errors in management systems, such as exposed APIs or excessive container privileges, can serve as an entry point for attackers.
To protect containerized environments, organizations apply a DevSecOps approach. This includes using minimized (containing nothing superfluous) and trusted images, updating them regularly, and automatically scanning them during the build phase. It also involves limiting process privileges, and segmenting network traffic within the cluster.