rkt - App Container runtime
rkt (pronounced "rock-it") is a CLI for running app containers on Linux. rkt is designed to be composable, secure, and fast.
Some of rkt's key features and goals include:
- First-class integration with init systems (systemd, upstart) and cluster orchestration tools (fleet, Kubernetes)
- Compatibility with other container software (e.g. rkt can run Docker images)
- Modular and extensible architecture (network configuration plugins, swappable execution engines based on systemd or QEMU/KVM)
For more on the background and motivation behind rkt, read the original launch announcement.
rkt is maturing rapidly while under active development, and its interfaces are not yet considered stable. We do not recommend its use in production, but we encourage you to try out rkt and provide feedback via issues and pull requests.
Check out the roadmap for more details on the future of rkt.
Trying out rkt
Using rkt on Linux
rkt consists of a single self-contained CLI, and is currently supported on amd64 Linux. A modern kernel is required but there should be no other system dependencies. We recommend booting up a fresh virtual machine to test out rkt.
To download the
rkt binary, simply grab the latest release directly from GitHub:
wget https://github.com/coreos/rkt/releases/download/v0.10.0/rkt-v0.10.0.tar.gz tar xzvf rkt-v0.10.0.tar.gz cd rkt-v0.10.0 ./rkt help
Trying out rkt using Vagrant
For Mac (and other Vagrant) users we have set up a
Vagrantfile: clone this repository and make sure you have Vagrant 1.5.x or greater installed.
vagrant up starts up a Linux box and installs via some scripts
actool. With a subsequent
vagrant ssh you are ready to go:
git clone https://github.com/coreos/rkt cd rkt vagrant up vagrant ssh
Keep in mind while running through the examples that right now
rkt needs to be run as root for most operations.
Building App Container Images (ACIs)
rkt's native image format is ACI, defined in the App Container spec.
To build ACIs, a simple way to get started is by using
Another good resource is the appc build repository which has resources for building ACIs from a number of popular projects and languages.
There are also tools for converting Docker images to ACIs (although note that rkt can also run Docker images natively directly from Docker repositories by using this library internally).
Downloading an App Container Image (ACI)
rkt uses content addressable storage (CAS) for storing an ACI on disk. In this example, the image is downloaded and added to the CAS. Downloading an image before running it is not strictly necessary (if it is not present, rkt will automatically retrieve it), but useful to illustrate how rkt works.
$ sudo rkt trust --prefix=coreos.com/etcd Prefix: "coreos.com/etcd" Key: "https://coreos.com/dist/pubkeys/aci-pubkeys.gpg" GPG key fingerprint is: 8B86 DE38 890D DB72 9186 7B02 5210 BD88 8818 2190 CoreOS ACI Builder <firstname.lastname@example.org> Are you sure you want to trust this key (yes/no)? yes Trusting "https://coreos.com/dist/pubkeys/aci-pubkeys.gpg" for prefix "coreos.com/etcd". Added key for prefix "coreos.com/etcd" at "/etc/rkt/trustedkeys/prefix.d/coreos.com/etcd/8b86de38890ddb7291867b025210bd8888182190"
In Documentation, you can find a detailed, step-by-step guide for the signing procedure.
Now that we've trusted the CoreOS public key, we can fetch the ACI using
$ sudo rkt fetch coreos.com/etcd:v2.0.4 rkt: searching for app image coreos.com/etcd:v2.0.4 rkt: fetching image from https://github.com/coreos/etcd/releases/download/v2.0.4/etcd-v2.0.4-linux-amd64.aci Downloading aci: [========================================== ] 3.47 MB/3.7 MB Downloading signature from https://github.com/coreos/etcd/releases/download/v2.0.0/etcd-v2.0.4-linux-amd64.aci.asc rkt: signature verified: CoreOS ACI Builder <email@example.com> sha512-1eba37d9b344b33d272181e176da111e
Sometimes you will want to download an image from a private repository. This usually involves passing usernames and passwords or other kinds of credentials to the server. rkt currently supports authentication via configuration files. You can find configuration file format description (with examples!) in configuration documentation.
For the curious, we can see the files written to disk in rkt's CAS:
$ find /var/lib/rkt/cas/blob/ /var/lib/rkt/cas/blob/ /var/lib/rkt/cas/blob/sha512 /var/lib/rkt/cas/blob/sha512/1e /var/lib/rkt/cas/blob/sha512/1e/sha512-1eba37d9b344b33d272181e176da111ef2fdd4958b88ba4071e56db9ac07cf62
Per the App Container Specification, the SHA-512 hash is of the tarball and can be reproduced with other tools:
$ wget https://github.com/coreos/etcd/releases/download/v2.0.4/etcd-v2.0.4-linux-amd64.aci ... $ gzip -dc etcd-v2.0.4-linux-amd64.aci > etcd-v2.0.4-linux-amd64.tar $ sha512sum etcd-v2.0.4-linux-amd64.tar 1eba37d9b344b33d272181e176da111ef2fdd4958b88ba4071e56db9ac07cf62cce3daaee03ebd92dfbb596fe7879938374c671ae768cd927bab7b16c5e432e8 etcd-v2.0.4-linux-amd64.tar
Launching an ACI
After it has been retrieved and stored locally, an ACI can be run by pointing
rkt run at either the original image reference (in this case, "coreos.com/etcd:v2.0.4"), the full URL of the ACI, or the ACI hash. Hence, the following three examples are equivalent:
# Example of running via ACI name:version $ sudo rkt run coreos.com/etcd:v2.0.4 ... Press ^] three times to kill container
# Example of running via ACI hash $ sudo rkt run sha512-1eba37d9b344b33d272181e176da111e ... Press ^] three times to kill container
# Example of running via ACI URL $ sudo rkt run https://github.com/coreos/etcd/releases/download/v2.0.4/etcd-v2.0.4-linux-amd64.aci ... Press ^] three times to kill container
In the latter case,
rkt will do the appropriate ETag checking on the URL to make sure it has the most up to date version of the image.
Note that the escape character
^] is generated by
Ctrl-] on a US keyboard. The required key combination will differ on other keyboard layouts. For example, the Swedish keyboard layout uses
Ctrl-å on OS X and
Ctrl-^ on Windows to generate the
^] escape character.
Due to a bug in the Linux kernel, using rkt's overlay support on top of an overlay filesystem requires Linux 4.3+.
Contributing to rkt
rkt is an open source project under the Apache 2.0 license, and contributions are gladly welcomed! See the Hacking Guide for more information on how to build and work on rkt. See CONTRIBUTING for details on submitting patches and the contribution workflow.