Disclaimer
Note that this document is just a draft. These aren't official, approved Fedora guidelines.
Overview
The goal of this document is to describe how to create valid module files, document purposes of all the data fields in them, hint best practices and demonstrate some examples.
Each module is defined by a single YAML file and comprises of a number of key-value pairs describing the module's properties and components it contains. Not everything needs to (or even should) be filled in by the module packager; some of the fields get populated later during the module build or distribution phase. The module file format is commonly known as modulemd.
The original format specification can be found in the modulemd repository.
Required fields
Document header and the data section
Every modulemd file MUST contain a modulemd document header which consists of the document type tag and the document format version, and a data section holding the module data.
document: modulemd
version: 1
data:
(...)
The version is an integer and denotes the version of the metadata format the rest of the document is written in. As of now, only one officialy released version of the format exists, version 1.
Module summary and description
Every module MUST include human-readable short summary and description. Both should be written in US English.
summary: An example module
description: >
An example long description of an example module, written just
to demonstrate the purpose of this field.
The summary is a one sentence concise description of the module and SHOULD NOT end in a period.
The description expands on this and SHOULD end in a period. Description SHOULD NOT contain installation instructions or configuration manuals.
Module licensing
Every module MUST contain a license section and declare a list of the module's licenses. Note these aren't the module's components' licenses.
license:
module:
- MIT
Fedora content, such as SPEC files or patches not included upstream, uses the MIT license by default, unless the component packager declares otherwise. Therefore MIT might be a reasonable default for most module authors as well.
See Fedora_Packaging_Guidelines_for_Modules#Module_content_licensing to see how to declare components' licenses.
Optional fields
Module name, update stream and version
Every module SHOULD define its name, update stream and version.
name: example stream: another-example version: 20161109235500
Note, however, that module packagers SHOULD NOT define these values manually but rather expect the Module Build Service to do it for them, using the module's dist-git repository name as the module name, the dist-git repository branch name as the stream name and the particular commit timestamp as the version. This simplifies module rebuilds and moving modules between branches or repositories.
Packagers MAY override this behaviour by defining these fields themselves. This behavior may change in the future.
There are currently no formal restrictions for the format of the name and stream properties. The version, however, must be an unsigned integer.
Module content licensing
If the module includes some RPM or non-RPM content, the packager MAY also define a list of content licenses.
license:
module:
- MIT
content:
- GPL+
- BSD
Not every module includes packages and therefore doesn't necessarily have to include this field.
Furthermore, the content licenses list should ideally be automatically filled by module build tools rather than the module author.
Module dependencies
Modules MAY depend on other modules. These module relationships are listed in the depepdencies section. Dependencies are expressed using module names and their stream names.
dependencies:
buildrequires:
generational-core: master
requires:
generational-core: master
So far modulemd supports two kinds of dependencies:
buildrequiresfor listing build dependencies of the module, i.e. modules that define the buildroot for building the module's components; this will typically be thegenerational-coremodule, at minimumrequiresfor listing runtime dependencies of the module, i.e. modules that need to be available on the target system for this module to work properly; this too will typically be thegenerational-coremodule, at minimum
Either or both of these sections may be omitted, if necessary.
Extensible module metadata block
Modules MAY also contain an extensible metadata block, a list of vendor-defined key-value pairs.
xmd:
user-defined-key: 42
another-user-defined-key:
- the first value of the list
- the second value of the list
Module references
Modules MAY define links referencing various upstream resources, such as community website, project documentation or upstream bug tracker.
references:
community: http://www.example.com/
documentation: http://www.example.com/docs/1.23/
tracker: http://www.example.com/bugs/
Module profiles
The module author MAY define lists of packages that would be installed by default, and a minimum, when the module is enabled and the particular profile is selected. Whether the packages actually get installed depends on the user's configuration. It is possible to define a profile that doesn't install any packages.
Profile names are arbitrary strings. There is currently one special-purpose profile name defined — default. More special-purpose profile names might be defined in the future.
The default profile lists packages that would be installed unless the user's configuration dictates otherwise.
In the case of RPM content, the profile package lists reference binary RPM package names.
profiles:
default:
rpms:
- myapplication
- myapplication-plugins
minimal:
description: An example minimal profile installing only the myapplication package.
rpms:
- myapplication
Module API
TBD
Module filters
TBD
Module components
Modules MAY, and most modules do contain a components section defining the module's content.
components:
(...)
RPM content
Module RPM content is defined in the rpms subsection of components and typically consists of one or more packages described by their SRPM names and additional extra key-value pairs, some required and some optional, associated with them.
components:
rpms:
foo:
rationale: The key component of this module
repository: git://git.example.com/foo.git
ref: branch-tag-or-commit-hash
cache: http://www.example.com/lookasidecache/
arches:
- i686
- x86_64
multilib:
- x86_64
The following key-value pairs extend the SRPM name:
rationale- every component MUST declare why it was added to the module; this is currently a free form string. It should end with a period.buildorder- TBDrepository- specifies git or other VCS repository to use as the component's source; in Fedora, dist-git is used and this option cannot be overridden.ref- therepositoryreference (a branch or tag name or a commit hash) that should be built and included in this module; recommended. If not defined, the current HEAD or equivalent is used.refis always populated by the exact commit hash used by the Module Build System during build.cache- points to RPM lookaside cache; in Fedora this option cannot be overriden.arches- a list of architectures this component should be built for; defaults to all available architectures.multilib- a list of architectures where this component should be available as multilib, e.g. ifx86_64is listed, x86_64 repositories will also include i686 builds. Defaults to no multilib.
Module content
TBD
Other content
No other content is currently supported.
Examples
Minimal module
A minimal module distributed as example-master-20161109172409, stored in the modules/example dist-git repository and its master branch, built on November 9, 2016, at 17:24:09 UTC, containing no packages, having no dependencies whatsoever and defining only the minimal set of required metadata.
document: modulemd
version: 1
data:
summary: An example summary
description: And an example description.
license:
module:
- MIT
Minimal module with RPM content
Another flavour of the abovementioned module, containing one RPM package with SRPM name foo. This module doesn't define any dependencies or optional metadata.
document: modulemd
version: 1
data:
summary: An example summary
description: And an example description.
license:
module:
- MIT
components:
rpms:
foo:
rationale: An example RPM component.
Minimal module with RPM content but with the -docs subpackage excluded
Yet another flavour of the minimal module, containing one RPM package with SRPM name foo. A build of 'foo' creates binary packages 'foo-1.0-1' and the subpackage 'foo-doc-1.0-1'. Both would get included in the module for any architecture if no filter were be used. This module doesn't define any dependencies or optional metadata.
document: modulemd
version: 1
data:
summary: An example summary
description: And an example description.
license:
module:
- MIT
filter:
rpms:
- foo-docs
components:
rpms:
foo:
rationale: An example RPM component.
Minimal module with dependencies only (a variant of stack)
Another minimal module, containing no packages or any optional metadata besides dependencies. Modules of this type are, together with modules that include other modules, referred to as stacks.
document: modulemd
version: 1
data:
summary: An example summary
description: And an example description.
license:
module:
- MIT
dependencies:
requires:
generational-core: master
a-framwork-module: and-its-stream
Minimal module which includes another (another variant of stack)
TBD
document: modulemd
version: 1
data:
summary: An example summary
description: And an example description.
license:
module:
- MIT
content:
modules:
a-framework-module:
rationale: Bundled for various reasons.
Common Fedora module
A typical Fedora module defines all the mandatory metadata plus some useful references, has build and runtime dependencies and contains one or more packages built from specific refs in dist-git. It relies on the Module Build Service to extract the name, stream and version properties from the VCS data and to fill in the licensing information from the included components and populate the data→license→content list.
document: modulemd
version: 1
data:
summary: An example of a common Fedora module
description: This module demonstrates what most Fedora modules look like.
license:
module: [ MIT ]
dependencies:
buildrequires:
generational-core: master
extra-build-environment: master
requires:
generational-core: master
references:
community: http://www.example.com/common-package
documentation: http://www.example.com/common-package/docs/5.67/
profiles:
default:
rpms:
- common-package
- common-plugins
development:
rpms:
- common-package
- common-package-devel
- common-plugins
api:
rpms:
- common-package
- common-package-devel
- common-plugins
components:
rpms:
common-package:
rationale: The key component of this module.
ref: common-release-branch
common-plugins:
rationale: Extensions for common-package.
buildorder: 1
ref: common-release-branch