runC – Open Container Initiative
Jeeva S. Chelladhurai
https://www.linkedin.com/in/jeevachelladhurai/
@Docker Meetup #34
Author of Learning Docker
https://www.packtpub.com/networking-and-servers/learning-docker-second-edition

About OCI
• Open Container Initiative
• Open Industry Standard
• Common, minimal, open standards and specification
• Container Format and Runtime
• Linux Foundation Collaborative Project
• Launched June 22 2015
• Docker, CoreOS and etc.
• Docker donated libcontainer
• https://github.com/opencontainers/runc

Why OCI
• Removes vendor lock-in
• Portability
• Interoperability
• Agility
• Rootless container
• Init system & Cron integration

OCI Scope [1/4]
• Runtime executable reference
• OCI Base Layer
• RunC - reference implementation
• https://github.com/opencontainers/runc
• Runtime Spec
• OCI Base Layer
• https://github.com/opencontainers/runtime-spec
• Defines the parameters needed to run the container

OCI Scope [2/4]
• Bundle Format
• OCI Base Layer
• https://github.com/opencontainers/image-spec
• Defines the filesystem layout
• Standardization needed for various runtimes
• Hashing for Content Integrity
• OCI Base Layer
• https://github.com/opencontainers/go-digest
• Ensure content integrity

OCI Scope [3/4]
• Content Addressable name
• OCI Base Layer
• Using hash as address for immutable containers
• Early stage of discussion
• Archival Format
• OCI Base Layer
• Serialization of filesystem bundle
• Yet to start

OCI Scope [4/4]
• Compliance Test Suite
• OCI Base Layer
• Test cases and tools to ensure the implementations comply with the
specs
• OCI Optional Layers
• Signature
• DNS based naming

runC
• Client wrapper around libcontainer
• libcontainer is OS interface
• runC requires
• OCI config (json)
• OCI bundle (filesystem)

Environment
• Vagrant https://www.vagrantup.com
• VirtualBox https://www.virtualbox.org
• Vagrant Box used: ubuntu/xenial64
• vagrant flow
 create a directory in the host system, and from that directory run below
vagrant commands
 vagrant init ubuntu/xenial64
 vagrant ssh

Installing runC thru docker
• Docker uses runC as its runtime
• It is shipped with docker as docker-runc
ubuntu@ubuntu-xenial:~$ docker --version
Docker version 17.06.0-ce, build 02c1d87
ubuntu@ubuntu-xenial:~$ docker-runc --version
runc version 1.0.0-rc3
commit: 2d41c047c83e09a6d61d464906feb2a2f3c52aa4
spec: 1.0.0-rc5

Installing runC from Release
• Release binary can be downloaded from
https://github.com/opencontainers/runc/releases/

Installing runC from source
• install go lang 1.8.3 (might work with older versions too)
• set GOROOT & GOPATH path
• also install libseccomp-dev, gcc, make, pkg-config
• cd $GOPATH/src/github.com/opencontainers
• git clone https://github.com/opencontainers/runc
• cd runc && make && sudo make install
ubuntu@ubuntu-xenial:~$ runc --version
runc version 1.0.0-rc4+dev
commit: ae2948042b08ad3d6d13cd09f40a50ffff4fc688
spec: 1.0.0

runc CLI

docker-runc CLI

OCI runC flow
nnkn
Config.json
-platform
-env
-user
-hostname
-root
+ r
rootfs
/
bin/
etc/
home/
opt/
……
Container
Runtime
ContainerContainer
Filesystem Bundle

Creating an OCI Bundle
1. Choose a directory
$ cd ${HOME}/myalpine
2. Create rootfs
$ mkdir rootfs
3. Create a docker container
$ docker create --name myalpine alpine
4. Export the container to a tar file
$ docker container export myalpine -o myalpine.tar
5. Untar the file into rootfs
$ tar -C rootfs -xvf myalpine.tar
6. Generate config.json spec
$ runc spec

Create a bundle in a single stroke
1. Choose a directory
$ cd ${HOME}/myalpine2
2. Create rootfs
$ mkdir rootfs
3. Create bundle with chain of commands
$ docker export $(docker create alpine) | tar -C rootfs -xvf -
4. Generate config.json spec
$ runc spec

Running your first runc container
1. Change to the OCI Bundle directory
$ cd ${HOME}/myalpine
2. Run the alpine bundle as root
$ sudo runc run myalpine

config.json snippet

Working with spec
false
“ip”, “addr”
Remove netwrok namespace
for host network

runc on host network
config.json https://gist.github.com/sjeeva/903de797838882082af7921bac5fbfd4

rootless containers
• Running container as non-root user
• runc binary should be owned by root
• Create a spec for rootless container
• runc spec --rootless
• Launch runc with --root option
• runc --root /tmp/runc run myalpine

Mounting host directories
• Edit the config.json spec and added the mount point to the
mounts section
• Example:

Hooks
• Supports three hooks to perform specific action
• prestart – before launching the container
• poststart – after launching the user process inside the container
• poststop – after stopping the user process inside the container

Thank You
https://www.linkedin.com/in/jeevachelladhurai/