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Published: Oct 6, 2022 License: Apache-2.0 Imports: 19 Imported by: 0



The imaginator daemon builds OS and OS+application images which are specified by image manifests.

Status page

The imaginator provides a web interface on port 6975 which shows a status page, links to built-in dashboards and access to performance metrics and logs. If imaginator is running on host myhost then the URL of the main status page is http://myhost:6975/. An RPC over HTTP interface is also provided over the same port.


Imaginator is started at boot time, usually by one of the provided init scripts. The imaginator process is baby-sat by the init script; if the process dies the init script will re-start it. It may be stopped with the command:

service imaginator stop

which also kills the baby-sitting init script. It may be started with the comand:

service imaginator start

There are many command-line flags which may change the behaviour of imaginator, generally with defaults which should be adequate for most deployments. Built-in help is available with the command:

imaginator -h
Key configuration parameters

The init script reads configuration parameters from the /etc/default/imaginator file. The following is the minimum likely set of parameters that will need to be configured.

The CONFIGURATION_URL variable specifies the main configuration URL, which may be a local file or a HTTP URL. It is recommended to specify a HTTP URL which references a file in a Git repository.

The IMAGE_SERVER_HOSTNAME variable specifies the hostname where the imageserver is running. This hostname must be resolvable by the imaginator.

The VARIABLES_FILE variable specifies an optional filename from which to read special variables which may be used for variable expansion. These are typically used to store secrets for accessing Git repositories which require authentication. Each line should contain a single NAME=Value entry.


RPC access is restricted using TLS client authentication. Imaginator expects a root certificate in the file /etc/ssl/CA.pem which it trusts to sign certificates which grant access. It also requires a certificate and key which grant it the ability to add and get images and objects from the imageserver. These should be in the files /etc/ssl/imaginator/cert.pem and /etc/ssl/imaginator/key.pem, respectively.


The builder-tool utility may be used to request the imaginator to build an image.

Main Configuration URL

The main configuration URL points to a JSON encoded file that describes all the image streams and how to build them. The top-level JSON object should contain the following fields:

  • BootstrapStreams: a table of bootstrap image stream names and their respective configurations
  • ImageStreamsToAutoRebuild: an array of image stream names that should be rebuilt periodically, in addition to bootstrap streams that are always rebuilt automatically
  • ImageStreamsUrl: the URL of a configuration file containing a list of all the user-defined image streams
  • PackagerTypes: a table of packager type names (i.e. deb and rpm) and their respective configurations

A sample configuration file is provided which may be modified to suit your environment. This is a fully working configuration and only requires modification of the location of the package repositories and the ImageStreamsUrl for your custom image streams.

Bootstrap Streams configuration

Each bootstrap stream is configured by a JSON object with the following fields:

  • BootstrapCommand: an array of strings containing the bootstrap script to run to generate the image contents (typically debootstrap and yumbootstrap). The $dir variable expands to the root directory of the image to build
  • FilterLines: an array of regular expressions matching files which should not be included in the image
  • PackagerType: the name of the packager type to use
Image Streams URL

This is a JSON encoded configuration file listing all the user-defined image streams. It contains a top-level Streams field which in turn contains a table of image stream names and their respective configurations. The configuration for an image stream is a JSON object with the following fields:

  • ManifestUrl: the URL of a Git repository containing the image manifest for the image. The special URL scheme dir points to a local directory tree. Variables specified in the VARIABLES_FILE will be expanded here
  • ManifestDirectory: the directory within the Git repository containing the image manifest for the image. If unspecified, the top-level directory in the repository is used. The $IMAGE_STREAM variable expands to the name of the image stream

An example configuration file is provided. Note the use of variables in different places.

Packager Types

Each packager type is configured by a JSON object with the following fields:

  • CleanCommand: an array of strings containing the command to run when cleaning up packager debris
  • InstallCommand: an array of strings containing the command to run when installing packages. The name of the package to be installed is appended to the command-line
  • ListCommand: a JSON object defining how to list packages which are installed. This JSON object contains the following fields:
    • ArgList: an array of strings containing the command to run when listing installed packages
    • SizeMultiplier: an optional multiplier to apply to the output of the listing command to convert the size result to Bytes
  • UpdateCommand: an array of strings containing the command to run when updating the package database
  • UpgradeCommand: an array of strings containing the command to run when upgrading the already installed packages
  • Verbatim: an array of strings containing commands to run before any of the above defined commands

These parameters are used to generate a /bin/generic-packager script which is used as an interface to the native OS packaging tools.


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