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rkt and App Container 0.2.0 Release

This week both rkt and the App Container (appc) spec have reached 0.2.0. Since our launch of the projects in December, both have been moving very quickly with a healthy community emerging. rkt now has cryptographic signing by default and a community is emerging around independent implementations of the appc spec. Read on for details on the updates.

rkt 0.2.0

Development on rkt has continued rapidly over the past few weeks, and today we are releasing v0.2.0. This important milestone release brings a lot of new features and improvements that enable securely verified image retrieval and tools for container introspection and lifecycle management.

Notably, this release introduces several important new subcommands:

  • rkt enter, to enter the namespace of an app within a container
  • rkt status, to check the status of a container and applications within it
  • rkt gc, to garbage collect old containers no longer in use

In keeping with rkt's goals of being simple and composable, we've taken care to implement these lifecycle-related subcommands without introducing additional daemons or databases. rkt achieves this by taking advantage of existing file-system and kernel semantics like advisory file-locking, atomic renames, and implicit closing (and unlocking) of open files at process exit.

v0.2.0 also marks the arrival of automatic signature validation: when retrieving an image during rkt fetch or rkt run, Rocket will verify its signature by default. Kelsey Hightower has written up an overview guide explaining this functionality. This signature verification is backed by a flexible system for storing public keys, which will soon be even easier to use with a new rkt trust subcommand. This is a small but important step towards our goal of rkt being as secure as possible by default.

Here's an example of the key validation in action when retrieving the latest etcd release (in this case the CoreOS ACI signing key has previously been trusted using the process above):

$ rkt fetch
rkt: searching for app image
rkt: fetching image from
Downloading aci: [=============================                ] 2.31 MB/3.58 MB
Downloading signature from
rkt: signature verified:
  CoreOS ACI Builder <>

App Container 0.2.0

The appc spec continues to evolve but is now stabilizing. Some of the major changes are highlighted in the announcement email that went out earlier this week.

This last week has also seen the emergence of two different implementations of the spec: jetpack (a FreeBSD/Jails-based executor) and libappc (a C++ library for working with app containers). The authors of both projects have provided extremely helpful feedback and pull requests to the spec, and it is great to see these early implementations develop!

Jetpack, App Container for FreeBSD

Jetpack is an implementation of the App Container Specification for FreeBSD. It uses jails as an isolation mechanism, and ZFS for layered storage. Jetpack is a great test of the cross platform portability of appc.

libappc, C++ library for App Container

libappc is a C++ library for doing things with app containers. The goal of the library is to be a flexible toolkit: manifest parsing and creation, pluggable discovery, image creation/extraction/caching, thin-provisioned file systems, etc.

Get involved

If you are interested in contributing to any of these projects, please get involved! A great place to start is issues in the Help Wanted label on GitHub. You can also reach out with questions and feedback on the Rocket and appc mailing lists:


App Container

In the SF Bay Area or NYC next week? Come to the meetups in each area to hear more about these changes and the future of rocket and appc. RSVP to the CoreOS NYC meetup and SF meetup to learn more.

Lastly, thank you to the community of contributors emerging around Rocket and App Container:

Alan LaMielle, Alban Crequy, Alex Polvi, Ankush Agarwal, Antoine Roy-Gobeil, azu, beadon, Brandon Philips, Brian Ketelsen, Brian Waldon, Burcu Dogan, Caleb Spare, Charles Aylward, Daniel Farrell, Dan Lipsitt, deepak1556, Derek, Emil Hessman, Eugene Yakubovich, Filippo Giunchedi, Ghislain Guiot, gprggr, Hector Fernandez, Iago López Galeiras, James Bayer, Jimmy Zelinskie, Johan Bergström, Jonathan Boulle, Josh Braegger, Kelsey Hightower, Keunwoo Lee, Krzesimir Nowak, Levi Gross, Maciej Pasternacki, Mark Kropf, Mark Lamourine, Matt Blair, Matt Boersma, Máximo Cuadros Ortiz, Meaglith Ma, PatrickJS, Pekka Enberg, Peter Bourgon, Rahul, Robo, Rob Szumski, Rohit Jnagal, sbevington, Shaun Jackman, Simone Gotti, Simon Thulbourn, virtualswede, Vito Caputo, Vivek Sekhar, Xiang Li