  This paper describes how we have sustained the Montage image mosaic engine
(http://montage.ipac.caltech.edu) first released in 2002, to support the
ever-growing scale and complexity of modern data sets. The key to its longevity
has been its design as a toolkit written in ANSI-C, with each tool performing
one distinct task, for easy integration into scripts, pipelines and workflows.
The same code base now supports Windows, JavaScript and Python by taking
advantage of recent advances in compilers. The design has led to applicability
of Montage far beyond what was anticipated when Montage was first built, such
as supporting observation planning for the JWST. Moreover, Montage is highly
scalable and is in wide use within the IT community to develop advanced,
fault-tolerant cyber-infrastructure, such as job schedulers for grids, workflow
orchestration, and restructuring techniques for processing complex workflows
and pipelines.
