In the growing world of container technology for application virtualization, Docker isn't the only game in town. CoreOS today announced an expansion of its application container specification (appc) effort to include the support of Apcera, Google, Red Hat and VMware.

The appc effort first began back in December 2014, when CoreOS announced its Rocket container technology as an alternative to Docker. CoreOS builds its own container-optimized operating system that uses Docker, though CoreOS developers have not been entirely happy with the way Docker has been progressing. With appc, the basic idea is to build an open-source specification for containers that isn't tied to any one vendor or technology.

Apcera, Google, Red Hat and VMware are supporting appc in different ways, said Alex Polvi, CoreOS CEO. "Google has furthered its support of appc by implementing rkt [Rocket] into Kubernetes and joining as a maintainer of appc," Polvi told eWEEK. " VMware recently announced how they will contribute to appc and shipped rkt in Project Photon."

While Apcera has announced an additional appc implementation called Kurma, Red Hat has assigned an engineer to participate as a maintainer of appc.

As an open effort, there are now five maintainers for the appc initiative:

Vincent Batts, Red Hat senior software engineer; Tim Hockins, Google senior staff software engineer; Charles Aylward, Twitter software engineer; Brandon Philips, CoreOS CTO; and Jonathan Boulle, CoreOS senior engineer.

The governance model for appc has also been publicly posted in Github to provide full transparency into how appc is being developed.

While Docker is perhaps the best-known example of application container virtualization, there is no overlap between the appc effort and Docker today, Polvi said. "Also, Docker, at any version, does not support appc," he said.

The key promise of appc, according to Polvi, is to define an interchangeable image that can be run on multiple container implementations.

"So, the compatibility that we are aiming for is someone who packages up an image to run on top, or rkt should run another compatible runtime such as Kurma," Polvi explained. "This promise of having portability was something that the industry didn't quite achieve with virtual machines and cloud.

Both rkt and Kurma will support Application Container Images (ACIs); that's where the compatibility will reside, Polvi said. Both Kurma and rkt support the ACI discovery methods as defined by the appc spec.

"Anyone who invests in creating ACIs will benefit from the fact that rkt and Kurma can discover and run them," Polvi said.

The next major step is to continue to work together on a standard on which all supporting companies can agree, Polvi said. He noted that the next major milestone is creating a 1.0 version of appc that remains stable for implementations to use.

Quay

In addition to the expanded support for appc, CoreOS today announced new features for its Quay container repository platform. Among the features is a simplified user interface and support for the Bitbucket and Gitlab code repositories.

Quay, which CoreOS acquired in August 2014, is now an important part of the cmpany, according to Polvi.

Docker also has its own container repository effort known as Docker Registry.

"Quay is a full-service solution to building, storing and managing container images while the open-source Docker registry project provides only the most basic ability to push and pull images," Polvi said. "We see Quay as an integral part of the continuous deployment of containerized applications now and in the future."

Sean Michael Kerner is a senior editor at eWEEK and InternetNews.com. Follow him on Twitter @TechJournalist.