Hack the Container: Understanding Docker's Inner Workings
Docker Runtimes: An Overview
The container ecosystem includes multiple runtimes at each level. While all of them serve the purpose of running containers, they do so in different ways. Some of these runtimes are OCI-compliant, while others predate or extend beyond OCI. Some focus strictly on execution, while others incorporate additional capabilities such as:
- Image transfer and storage
- Container execution and supervision
- Low-level storage management
- Network attachment and configuration
Opinions vary on which runtime is best suited for specific use cases, but the default Docker runtimes (runC and containerd) are widely adopted and supported. The following table summarizes commonly used container runtimes and the layer at which they operate:
| Technology | Level | Specificity / Typical Usage |
|---|---|---|
| LXC | Low-level | Full system containers providing OS-level virtualization, often used to run multiple services per container or emulate lightweight virtual machines. |
| runC | Low-level | OCI reference runtime focused solely on creating and executing containers using Linux namespaces and cgroups. Used by most modern container platforms. |
| runhcs | Low-level | Windows-specific OCI runtime for running Windows containers, leveraging Windows kernel features for isolation. |
| crun | Low-level |
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