optionalg / smith

Smith: A microcontainer builder

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 smith

Building can be done via the Makefile:

make

Build dependencies:

golang-bin

Go dependencies are vendored in the vendor directory.

Runtime dependencies

To build from rpms, smith requires:

mock

Although mock is used for rpm packaging, it can be installed on debian/ubuntu if you are willing to be a little tricky. 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. Instructions for debian/ubuntu:

sudo apt-get install createrepo yum
# At the time of this writing the below package is suitable and available
# for download. Your milage may vary and we suggest finding an official
# debian mock package that is 1.2 or 1.3.
wget http://ftp.debian.org/debian/pool/main/m/mock/mock_1.3.2-1_all.deb
sudo dpkg -i mock_1.3.2-1_all.deb
usermod -a -G mock <your_username>
# 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

Installing smith

Installing can be done via the Makefile:

sudo make install

Installing smith using a Docker container

docker build -t smith .

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.

Build

To build a container with smith, create a smith.yaml file and invoke smith with no parameters:

mkdir cat
cd cat

cat >smith.yaml <<EOF
package: coreutils
paths:
- /usr/bin/cat
cmd:
- /usr/bin/cat
- /read/data
EOF

mkdir -p rootfs/read
echo "Hello World!" >rootfs/read/data

smith

Build using a Docker container

Run the container mounting smith.yaml folder:

mkdir cat
cd cat

cat >smith.yaml <<EOF
package: coreutils
paths:
- /usr/bin/cat
cmd:
- /usr/bin/cat
- /read/data
EOF

mkdir -p rootfs/read
echo "Hello World!" >rootfs/read/data

Build smith.yml:

docker run -it --rm \
--privileged -v $PWD:/write \
-v cache:/var/cache \
-v mock:/var/lib/mock vishvananda/smith

You can also use an alias to run smith commands from your host:

smith(){
    docker run -it --rm \
    --privileged -v $PWD:/write \
    -v cache:/var/cache \
    -v mock:/var/lib/mock vishvananda/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 $@
}

Advanced Usage

For more detailed instructions on building containers, check out 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.

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.