docktar

docktar

docktar is a small script / program that adds one or more binary files, with all dynamic libraries they need into a single tar archive file.

This allows for creating much smaller and easier to maintain docker images by adding only the data required.

It can, optionally, strip debugging symbols from binary files and add non-executable files, like configrations or data files, without processing them.

Important: docktar only works on linux systems with linux binaries!

Installation

With a properly setup go environment, go get will install the latest version:

go get github.com/garfieldius/docktar

Ready to use binaries can be found in the releases section. After the download they must be put into a directory in $PATH and marked executable.

Usage

Running docktar

Creating archives

docktar is started on a command line with one or several full filepaths as arguments.

docktar $(which gawk) /bin/sed

The file will have the same filepath within the tar archive. A different path is set by adding it after the source path, divided by a colon:

docktar /usr/bin/gawk:/bin/awk

If the file path is relative it will be expanded to absolute. Files in $PATH can be added without a directory in the argument. Docktar will add them with the directory they are found in.

docktar awk # Adds awk as "/usr/bin/awk"

Note that symlinks are resolved, but not added. So if the above example is a link to /usr/bin/gawk, the content of the link target is added under the name of the link itself.

The following three commands will create the same tar archive:

docktar awk
docktar $(which awk)
docktar $(readlink $(which awk)):/usr/bin/awk

Multiple files can be added with multiple arguments and/or globbing. When using the latter, escape the argument to ensure the pattern is not expaned by the shell:

# Add PHP for CLI and FPM, and all its extensions and ini files
docktar php php-fpm "/usr/lib/php/**/*.so" "/etc/php/**/*.ini"

Switches

By default, docktar will save the resulting archive in a file named docker.tar within the current working directory. The -o flag sets a different filename. Setting -o to - will write the archive to stdout:

docktar -o sed.tar /bin/sed
# or
docktar -o - /bin/sed > sed.tar

With the -s switch, all files will be stripped of debugging symbols. This required the program strip to be installed.

docktar -s $(which sed)

Adding -d creates a Dockerfile next to the written .tar file, containing the minimum commands to create an image.

Using the archive

A Dockerfile that starts from scratch and ADDs the archive into / will place the content of the archive into a new image.

With a Dockerfile like this:

FROM scratch

ADD docker.tar /

The image can be build and a container started:

% docktar /bin/sed
% docker build -t sed .
% docker run --rm sed /bin/sed
Usage: /bin/sed [OPTION]... {script-only-if-no-other-script} [input-file]...
...

Note: The Dockerfile example above is the same that is created with the -d switch.

License

(c) 2017 by Georg Großberger [email protected]

Licensed under the GPLv3 See the file LICENSE or https://www.gnu.org/licenses/gpl-3.0.html for details.