Tebako packager revisited

Tebako is an executable packager. It packages a Ruby solution with the key idea: one Ruby application => one Tebako image.

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Every image contains all the files the application needs to run and has no dependencies other than what is included in the targeted operating system. In fact, the Tebako algorithm is very simple. To create an executable package, Tebako executes five tasks:

• Create an access layer for DwarFS file system with minimal dependencies on external libraries.
• Build target version of Ruby with minimal dependencies on external libraries.
• Deploy a Ruby solution with all dependencies on the filesystem image.
• Patch Ruby so that it transparently uses the in-memory DwarFS image.
• Combine all together in a single executable.

The main complexity is related to the fulfillment of the «with minimal dependencies» condition for different operating systems.

Although GNU Linux (systems that use the GNU C Library glibc, musl Linux (systems that use musl libc, and macOS (which is BSD based) provide very similar sets of libraries, their names, dependencies, and packaging differ, and not always in a predictable and stable way.

Moreover, «with minimal dependencies» implies the use of static libraries, which is contrary to the current trend of preferring shared, dynamic libraries. For some packages, distributions only provide shared libraries, which means that the static version of the libraries need to be installed separately or from source.

These functions are split across five Tebako components and sub-components:

The description above shows that two copies of Ruby are used when creating the Tebako image:

• The host Ruby that must be pre-installed to run the Tebako gem.
• The target Ruby that Tebako loads sources for, patches, builds and transforms
  to Tebako image.

Version requirements for host Ruby are minimal. Tebako shall run on all 2.7 and 3.x versions.

In contrast, requirements for target Ruby are strict. Tebako 0.5.4 supports packaging of 2.7.7; 3.0.6; 3.1.4 and 3.2.2.

As mentioned above, the most complex Tebako tasks (tasks 1,2) are implemented by the setup subcomponent. As a prerequisite, they require the installation of distribution packages, which may be different for GNU Linux, musl Linux, and MacOS. Setup is a lengthy task that can take significant time, up to 2 hours.

The good news is that setup task only needs to be done once and it does not depend on solution being packaged.

Tebako offers an explicit tebako setup command or executes setup implicitly on the first attempt to create Tebako image.

Once setup has been completed, packaging of any bundle, gem, or simple Ruby script requires no additional configuration or preparation and can be done with a single tebako press command, which takes several minutes even for large packages.

In conclusion, I would like to emphasize once again that the most difficult task solved by Tebako is building a Ruby interpreter and an access layer for an in-memory file system with minimal dependencies on external libraries. This task is performed once, after which Tebako provides a one-line command to package any arbitrary complex Ruby application.