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Version: 1.5.0

What is Apptainer?

Apptainer is an open-source containerization software designed specifically for high-performance computing (HPC), scientific research, and environments requiring strong security. It enables users to create, manage, and run containers that package applications with their dependencies in a portable, reproducible, and isolated manner. It was originally known as Singularity and is popular in academic and research institutions due to its focus on HPC environments.

Relation to Singularity​

Apptainer is the continuation of Singularity under a new governance model. In 2021, the Singularity project moved under the Linux Foundation, where it was rebranded as Apptainer to ensure the long-term sustainability and broader collaboration around the project. Functionally, Apptainer continues Singularity’s legacy, maintaining compatibility with its containers and focusing on the same core goals.

Why Use Apptainer Over Docker?

Apptainer and Docker are both containerization tools, but they cater to different needs and environments. Here are some key points comparing Apptainer to Docker:

  1. Designed for HPC and Research
  • Apptainer: Focuses on HPC environments, allowing non-privileged users to run containers on shared clusters. It integrates seamlessly with HPC job schedulers like SLURM and is compatible with shared filesystems.
  • Docker: Requires root privileges to run and is not ideal for HPC due to security concerns in multi-tenant systems.
  1. Security Features
  • Apptainer: Operates with a security model where containers are run as the user who invokes them, minimizing privilege escalation risks. It avoids running a daemon that requires elevated privileges.
  • Docker: Relies on a root-privileged daemon (dockerd), which can pose security risks in multi-user environments.
  1. Mobility of Compute
  • Apptainer: Containers are single, immutable files (SIF - Singularity Image Format) that can easily be copied, shared, and run on different systems without requiring special setup. This is particularly useful in environments where portability and reproducibility are critical.
  • Docker: Uses layered images stored in a local registry, which requires additional steps to share or move across systems.
  1. Simplicity for End Users
  • Apptainer: Users can directly execute containers without needing complex setups or root permissions.
  • Docker: Typically requires more infrastructure and configuration, especially in shared environments.
  1. Integration with Existing Tools
  • Apptainer: Better suited for integrating with HPC workflows and environments where Docker might not be permitted.
  • Docker: More suitable for general-purpose containerization, especially for web applications and services.

When to Use Apptainer​

If you are working in HPC, academic research, or other multi-user, secure environments. When you need portability and reproducibility without requiring elevated privileges. If you want easy integration with HPC tools like job schedulers or shared filesystems.

Docker remains a better choice for web development, CI/CD pipelines, and general-purpose applications in environments that permit its use. However, for scientific computing and HPC, Apptainer is the preferred solution.