smith - microcontainer builder

What is smith?

smith is a simple command line utility for building microcontainers from rpm packages or oci images.

Principles of microcontainers

1. A microcontainer only contains the process to be run and its direct dependencies.

2. The microcontainer has files with no user ownership or special permissions beyond the executable bit.

3. The root filesystem of the container should be able to run read-only. All writes from the container should be into a directory called /write. Any unique config that an individual container instance will need should be placed into a directory called /read. Ephemeral files such as pid files can be written to /run.

Building and Running smith

You can build and run smith either as:

• A Docker image
• A Binary

Both methods are described below, but the Docker route is recommended as the simplest and easiest option.

Docker based smith

Dependencies

• Docker

Method

1. Clone smith:

git clone https://github.com/oracle/smith.git

2. Build smith Docker image using the Dockerfile provided, optionally adding your own docker-repo-id to the tag:

sudo docker build -t [<docker-repo-id>/]smith .

3. Set up an alias (or script) to run smith from the command line:

smith(){
    sudo docker run -it --rm \
    --privileged -v $PWD:/write \
    -v cache:/var/cache \
    -v /tmp:/tmp \
    -v mock:/var/lib/mock [<docker-repo-id>/]smith [email protected]
}

You should now be able to start building microcontainers (see below).

Binary smith

Building can be done via the Makefile:

make

Dependencies

Build

• Docker
• Go

To install go run sudo yum install golang-bin or sudo apt install golang-go as appropriate

Go dependencies are vendored in the vendor directory.

Runtime

To build from RPMs, smith requires:

• mock

mock can have issues with non - RPM distros.

If you have problems installing or running smith natively on a non - RPM distro, best advice is to build it and run it in a Docker container (see above)

mock can be installed on Debian/Ubuntu with some extra care (see below). Specifically you need at least mock 1.2. Version 1.1.X will not work because the -r flag does not support abspath to the mock config file. Be aware that your smith builds may still fail.

Debian/Ubuntu specific instructions (Here be Dragons):

sudo apt install mock createrepo yum

# Fedora rawhide chroot (which mock uses by default) does not play well with
# Debian, so point /etc/mock/default.cfg to EPEL 7 (6 on Ubuntu):
sudo ln -s /etc/mock/epel-7-x86_64.cfg /etc/mock/default.cfg 

# rpm on Debian has a patch to macros that messes up mock so undo it. Note
# that updating your os will sometimes reset this file and you will have
# to run this command again.
sudo sed -i 's;%_dbpath\t.*;%_dbpath\t\t%{_var}/lib/rpm;g' /usr/lib/rpm/macros

# on debian/ubuntu for some reason yum tries to install packages for
# multiple archs, so it is necessary to update the yum.conf section in
# default.cfg to prevent that. If you switch your default.cfg you may
# have to do this again.
sudo sed -i '/\[main\]/a multilib_policy=best' /etc/mock/default.cfg

Whichever distro you are using check that your user is a member of the group mock:

$ groups

If your user is not a member of the group mock then add them:

$ usermod -aG mock <your_username>

On Oracle Linux edit your /etc/mock/site-defaults.cfg and add:

config_opts['use_nspawn'] = False

Installing smith

Installing can be done via the Makefile:

sudo make install

Using smith

To use smith, simply create a smith.yaml defining your container and run smith. If you want to overlay additional files or symlinks, simply place them into a directory called rootfs beside smith.yaml.

If you are building the same container multiple times without editing the package line, the -f parameter will rebuild the container without reinstalling the package.

Building Microcontainers

To build a "hello world" container with smith:

1. Create a new directory and cd to it

mkdir cat
cd cat

2. Create a smith.yaml file with the following contents:

package: coreutils
paths:
- /usr/bin/cat
cmd:
- /usr/bin/cat
- /read/data

3. Create the rootfs directory. Smith will put the contents of the ./rootfs directory into the root directory of the image.

mkdir rootfs

4. Create the read directory under rootfs

mkdir rootfs/read

5. Create the file data under rootfs/read with the following content:

Hello World!

• invoke smith with no parameters:

smith

Your image will be saved as image.tar.gz. You can change the name with a parameter:

smith -i cat.tar.gz

Smith has a few other options which can be viewed using "--help"

smith --help

Build Types

Smith can build from local rpm files or repositories. You can change the yum config by modifying your /etc/mock/default.cfg.

Smith can also build directly from oci files downloaded via the download command, or an oci directly from a docker repository. Simply specify either in your smith.yaml as package, for example:

package: https://registry-1.docker.io/library/fedora
paths:
- /usr/bin/cat
cmd:
- /usr/bin/cat
- /read/data

To build Smith directly from oci, the Docker command is slightly different:

smith(){
    docker run -it --rm \
    -v $PWD:/write \
    -v tmp:/tmp vishvananda/smith [email protected]
}

Advanced Usage

For more detailed instructions on building containers, check out:

• Smith Lab
• How To Build a Tiny Httpd Container

Upload

You can upload your image to a docker repository:

smith upload -r https://username:[email protected]/myrepo/cat -i cat.tar.gz

Images will be uploaded to the tag latest. You can specify an alternative tag name to use appending it after a colon:

smith upload -r https://registry-1.docker.io/myrepo/cat:newtag

It automatically uploads to registry-1.docker.io using docker media types. Otherwise it tries to upload using oci media types. If you want to upload to a private docker v2 registry that doesn't support oci media types, you can use the -d switch:

smith upload -d -r https://myregistry.com/myrepo/cat -i cat.tar.gz

You can specify a tag name to upload to by appending it to the name

Download

smith can also download existing images from docker repositories:

smith download -r https://registry-1.docker.io/library/hello-world -i hello-world.tar.gz

It will convert these to tar.gz oci layouts. The latest tag will be downloaded. To download an alternative tag, append it after a colon:

smith download -r https://registry-1.docker.io/library/hello-world:othertag

Contributing

Smith is an open source project. See CONTRIBUTING for details.

Oracle gratefully acknowledges the contributions to smith that have been made by the community.

Getting in touch

The best way to get in touch is Slack.

Click here to join the the Oracle Container Tools workspace.

Then join the Smith channel.

License

Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.

Smith is dual licensed under the Universal Permissive License 1.0 and the Apache License 2.0.

See LICENSE for more details.