Methods, systems, and computer storage media for providing a set of common flat files in a composite image that can be mounted as a container (i.e., composite container) to support isolation and interoperation of computing resources. Container management is provided for a container management system based on a composite image file system engine that executes composite operations to support resource isolation and operating system (OS) virtualization functionality. In particular, a container engine interface supports creating, mounting, and providing access to and from composite images or composite containers. In operation, a plurality of files for generating a composite image are accessed. The composite image for the plurality of files is generated. The composite image includes a set of common flat files. The composite image is communicated to cause mounting of the composite image, where mounting the composite image is based on a metadata file from the set of common flat files.