glibc and musl support in Docker Hardened Images

Docker Hardened Images (DHI) are built to prioritize security without sacrificing compatibility with the broader open source and enterprise software ecosystem. A key aspect of this compatibility is support for common Linux standard libraries: glibc and musl.

What are glibc and musl?#

When you run Linux-based containers, the image's C library plays a key role in how applications interact with the operating system. Most modern Linux distributions rely on one of the following standard C libraries:

• glibc (GNU C Library): The standard C library on mainstream distributions like Debian, Ubuntu, and Red Hat Enterprise Linux. It is widely supported and typically considered the most compatible option across languages, frameworks, and enterprise software.

• musl: A lightweight alternative to glibc, commonly used in minimal distributions like Alpine Linux. While it offers smaller image sizes and performance benefits, musl is not always fully compatible with software that expects glibc.

DHI compatibility#

DHI images are available in both glibc-based (e.g., Debian) and musl-based (e.g., Alpine) variants. For enterprise applications and language runtimes where compatibility is critical, we recommend using DHI images based on glibc.

What to choose, glibc or musl?#

Docker Hardened Images are available in both glibc-based (Debian) and musl-based (Alpine) variants, allowing you to choose the best fit for your workload.

Choose Debian-based (glibc) images if:

• You need broad compatibility with enterprise workloads, language runtimes, or proprietary software.
• You're using ecosystems like .NET, Java, or Python with native extensions that depend on glibc.
• You want to minimize the risk of runtime errors due to library incompatibilities.

Choose Alpine-based (musl) images if:

• You want a minimal footprint with smaller image sizes and reduced surface area.
• You're building a custom or tightly controlled application stack where dependencies are known and tested.
• You prioritize startup speed and lean deployments over maximum compatibility.

If you're unsure, start with a Debian-based image to ensure compatibility, and evaluate Alpine once you're confident in your application's dependencies.