lorax-composer¶

Authors:	Brian C. Lane <bcl@redhat.com>

lorax-composer is an API server that allows you to build disk images using Blueprints to describe the package versions to be installed into the image. It is compatible with the Weldr project’s bdcs-api REST protocol. More information on Weldr can be found on the Weldr blog.

Behind the scenes it uses livemedia-creator and Anaconda to handle the installation and configuration of the images.

Installation¶

The best way to install lorax-composer is to use sudo dnf install lorax-composer composer-cli, this will setup the weldr user and install the systemd socket activation service. You will then need to enable it with sudo systemctl enable lorax-composer.socket. This will leave the server off until the first request is made. Systemd will then launch the server and it will remain running until the system is rebooted.

Quickstart¶

Create a weldr user and group by running useradd weldr
Remove any pre-existing socket directory with rm -rf /run/weldr/ A new directory with correct permissions will be created the first time the server runs.
Enable the socket activation with systemctl enable lorax-composer.socket or run it directly with lorax-composer /path/to/blueprints/

The /path/to/blueprints/ directory is where the blueprints’ git repo will be created, and all the blueprints created with the /api/v0/blueprints/new route will be stored. If there are blueprint .toml files in the top level of the directory they will be imported into the blueprint git storage when lorax-composer starts.

Logs¶

Logs are stored under /var/log/lorax-composer/ and include all console messages as well as extra debugging info and API requests.

Security¶

Some security related issues that you should be aware of before running lorax-composer:

One of the API server threads needs to retain root privileges in order to run Anaconda.
SELinux must be set to Permissive or disabled to allow livemedia-creator to run Anaconda.
Only allow authorized users access to the weldr group and socket.

Since Anaconda kickstarts are used there is the possibility that a user could inject commands into a blueprint that would result in the kickstart executing arbitrary code on the host. Only authorized users should be allowed to build images using lorax-composer.

lorax-composer cmdline arguments¶

Lorax Composer API Server

usage: lorax-composer [-h] [--socket SOCKET] [--user USER] [--group GROUP]
                      [--log LOG] [--mockfiles MOCKFILES]
                      [--sharedir SHAREDIR] [-V] [-c CONFIG]
                      [--releasever STRING] [--tmp TMP] [--proxy PROXY]
                      BLUEPRINTS

Positional Arguments¶

BLUEPRINTS

Path to the blueprints

Named Arguments¶

`--socket`	Path to the socket file to listen on Default: “/run/weldr/api.socket”
`--user`	User to use for reduced permissions Default: “weldr”
`--group`	Group to set ownership of the socket to Default: “weldr”
`--log`	Path to logfile (/var/log/lorax-composer/composer.log) Default: “/var/log/lorax-composer/composer.log”
`--mockfiles`	Path to JSON files used for /api/mock/ paths (/var/tmp/bdcs-mockfiles/) Default: “/var/tmp/bdcs-mockfiles/”
`--sharedir`	Directory containing all the templates. Overrides config file sharedir
`-V`	show program’s version number and exit Default: False
`-c, --config`	Path to lorax-composer configuration file. Default: “/etc/lorax/composer.conf”
`--releasever`	Release version to use for $releasever in dnf repository urls
`--tmp`	Top level temporary directory Default: “/var/tmp”
`--proxy`	Set proxy for DNF, overrides configuration file setting.

How it Works¶

The server runs as root, and as weldr. Communication with it is via a unix domain socket (/run/weldr/api.socket by default). The directory and socket are owned by root:weldr so that any user in the weldr group can use the API to control lorax-composer.

At startup the server will check for the correct permissions and ownership of a pre-existing directory, or it will create a new one if it doesn’t exist. The socket path and group owner’s name can be changed from the cmdline by passing it the --socket and --group arguments.

It will then drop root privileges for the API thread and run as the weldr user. The queue and compose thread still runs as root because it needs to be able to mount/umount files and run Anaconda.

Composing Images¶

The welder-web GUI project can be used to construct blueprints and create composes using a web browser.

Or use the command line with composer-cli.

Blueprints¶

Blueprints are simple text files in TOML format that describe which packages, and what versions, to install into the image. They can also define a limited set of customizations to make to the final image.

Example blueprints can be found in the lorax-composer test suite, with a simple one looking like this:

name = "base"
description = "A base system with bash"
version = "0.0.1"

[[packages]]
name = "bash"
version = "4.4.*"

The name field is the name of the blueprint. It can contain spaces, but they will be converted to - when it is written to disk. It should be short and descriptive.

description can be a longer description of the blueprint, it is only used for display purposes.

version is a semver compatible version number. If a new blueprint is uploaded with the same version the server will automatically bump the PATCH level of the version. If the version doesn’t match it will be used as is. eg. Uploading a blueprint with version set to 0.0.1 when the existing blueprint version is 0.0.1 will result in the new blueprint being stored as version 0.0.1.

[[packages]] and [[modules]]¶

These entries describe the package names and matching version glob to be installed into the image.

The names must match the names exactly, and the versions can be an exact match or a filesystem-like glob of the version using * wildcards and ? character matching.

NOTE: As of lorax-composer-29.2-1 the versions are not used for depsolving, that is planned for a future release. And currently there are no differences between packages and modules in lorax-composer.

Customizations¶

The [[customizations]] section can be used to configure the hostname of the final image. eg.:

[[customizations]]
hostname = "baseimage"

[[customizations.sshkey]]¶

Set an existing user’s ssh key in the final image:

[[customizations.sshkey]]
user = "root"
key = "PUBLIC SSH KEY"

The key will be added to the user’s authorized_keys file.

[[customizations.user]]¶

Add a user to the image, and/or set their ssh key. All fields for this section are optional except for the name, here is a complete example:

[[customizations.user]]
name = "admin"
description = "Administrator account"
password = "$6$CHO2$3rN8eviE2t50lmVyBYihTgVRHcaecmeCk31L..."
key = "PUBLIC SSH KEY"
home = "/srv/widget/"
shell = "/usr/bin/bash"
groups = ["widget", "users", "wheel"]
uid = 1200
gid = 1200

If the password starts with $6$ , $5$ , or $2b$ it will be stored as an encrypted password. Otherwise it will be treated as a plain text password.

[[customizations.group]]¶

Add a group to the image. name is required and gid is optional:

[[customizations.group]]
name = "widget"
gid = 1130

Adding Output Types¶

livemedia-creator supports a large number of output types, and only some of these are currently available via lorax-composer. To add a new output type to lorax-composer a kickstart file needs to be added to ./share/composer/. The name of the kickstart is what will be used by the /compose/types route, and the compose_type field of the POST to start a compose. It also needs to have code added to the pylorax.api.compose.compose_args() function. The _MAP entry in this function defines what lorax-composer will pass to pylorax.installer.novirt_install() when it runs the compose. When the compose is finished the output files need to be copied out of the build directory (/var/lib/lorax/composer/results/<UUID>/compose/), pylorax.api.compose.move_compose_results() handles this for each type. You should move them instead of copying to save space.

If the new output type does not have support in livemedia-creator it should be added there first. This will make the output available to the widest number of users.

Example: Add partitioned disk support¶

Partitioned disk support is something that livemedia-creator already supports via the --make-disk cmdline argument. To add this to lorax-composer it needs 3 things:

A partitioned-disk.ks file in ./share/composer/
A new entry in the _MAP in pylorax.api.compose.compose_args()
Add a bit of code to pylorax.api.compose.move_compose_results() to move the disk image from the compose directory to the results directory.

The partitioned-disk.ks is pretty similar to the example minimal kickstart in ./docs/fedora-minimal.ks. You should remove the url and repo commands, they will be added by the compose process. Make sure the bootloader packages are included in the %packages section at the end of the kickstart, and you will want to leave off the %end so that the compose can append the list of packages from the blueprint.

The new _MAP entry should be a copy of one of the existing entries, but with make_disk set to True. Make sure that none of the other make_* options are True. The image_name is what the name of the final image will be.

move_compose_results() can be as simple as moving the output file into the results directory, or it could do some post-processing on it. The end of the function should always clean up the ./compose/ directory, removing any unneeded extra files. This is especially true for the live-iso since it produces the contents of the iso as well as the boot.iso itself.