Module Build Service Infra SOP

The MBS is a build orchestrator on top of Koji for "modules".

Contact Information


Release Engineering Team, Infrastructure Team


fedora-admin, #fedora-releng


jkaluza, fivaldi, breilly, mikem

Public addresses

  • mbs-frontend0[1-2]



Build modules for Fedora.


Users submit builds to referencing their modulemd file in dist-git. (In the future, users will not submit their own module builds. The freshmaker daemon (running in infrastructure) will watch for .spec file changes and modulemd.yaml file changes — it will submit the relevant module builds to the MBS on behalf of users.)

The request to build a module is received by the MBS flask app running on the mbs-frontend nodes.

Cursory validation of the submitted modulemd is performed on the frontend: are the named packages valid? Are their branches valid? The MBS keeps a copy of the modulemd and appends additional data describing which branches pointed to which hashes at the time of submission.

A fedmsg from the frontend triggers the backend to start building the module. First, tags and build/srpm-build groups are created. Then, a module-build-macros package is synthesized and submitted as an srpm build. When it is complete and available in the buildroot, the rest of the rpm builds are submitted.

These are grouped and limited in two ways:

  • First, there is a global NUM_CONCURRENT_BUILDS config option that controls how many koji builds the MBS is allowed to have open at any time. It serves as a throttle.

  • Second, a given module may specify that it’s components should have a certain "build order". If there are 50 components, it may say that the first 25 of them are in one buildorder batch, and the second 25 are in another buildorder batch. The first batch will be submitted and, when complete, tagged back into the buildroot. Only after they are available will the second batch of 25 begin.

When the last component is complete, the MBS backend marks the build as "done", and then marks it again as "ready". (There is currently no meaning to the "ready" state beyond "done". We reserved that state for future CI interactions.)

Observing MBS Behavior

The mbs-build command

The fm-orchestrator repo and the module-build-service package provide an mbs-build command with a few subcommands. For general help:

$ mbs-build --help

To generate a report of all currently active module builds:

$ mbs-build overview
  ID  State    Submitted             Components    Owner    Module
----  -------  --------------------  ------------  -------  -----------------------------------
 570  build    2017-06-01T17:18:11Z  35/134        psabata  shared-userspace-f26-20170601141014
 569  build    2017-06-01T14:18:04Z  14/15         mkocka   mariadb-f26-20170601141728

To generate a report of an individual module build, given its ID:

$ mbs-build info 569
NVR                                             State     Koji Task
----------------------------------------------  --------  ------------------------------------------------------------
libaio-0.3.110-7.module_414736cc                COMPLETE
libedit-3.1-17.20160618cvs.module_414736cc      COMPLETE
compat-openssl10-1.0.2j-6.module_414736cc       COMPLETE
policycoreutils-2.6-5.module_414736cc           COMPLETE
selinux-policy-3.13.1-255.module_414736cc       COMPLETE
systemtap-3.1-5.module_414736cc                 COMPLETE
libcgroup-0.41-11.module_ea91dfb0               COMPLETE
net-tools-2.0-0.42.20160912git.module_414736cc  COMPLETE
time-1.7-52.module_414736cc                     COMPLETE
desktop-file-utils-0.23-3.module_ea91dfb0       COMPLETE
libselinux-2.6-6.module_ea91dfb0                COMPLETE
module-build-macros-0.1-1.module_414736cc       COMPLETE
checkpolicy-2.6-1.module_414736cc               COMPLETE
dbus-glib-0.108-2.module_ea91dfb0               COMPLETE

To actively watch a module build in flight, given its ID:

$ mbs-build watch 570
Still building:

   2 components in the BUILDING state
   34 components in the COMPLETE state
   1 components in the FAILED state
   97 components in the undefined state
psabata's build #570 of shared-userspace-f26 is in the "build" state

The releng repo

There are more tools located in the scripts/mbs/ directory of the releng repo:

Cancelling a module build

Users can cancel their own module builds with:

$ mbs-build cancel $BUILD_ID

MBS admins can also cancel builds of any user.

MBS admins are defined as members of the groups listed in the ADMIN_GROUPS configuration options in roles/mbs/common/templates/


The frontend logs are on mbs-frontend0[1-2] in /var/log/httpd/error_log.

The backend logs are on mbs-backend01. Look in the journal for the fedmsg-hub service.


The package in question is module-build-service. Please use the playbooks/manual/upgrade/mbs.yml playbook.

Managing Bootstrap Modules

In general, modules use other modules to define their buildroots, but what defines the buildroot of the very first module? For this, we use "bootstrap" modules which are manually selected. For some history on this, see these tickets:

The tag for a bootstrap module needs to be manually created and populated by Release Engineering. Builds for that tag are curated and selected from other Fedora tags, with care to ensure that only as many builds are added as needed.

The existence of the tag is not enough for the bootstrap module to be useable by MBS. MBS discovers the bootstrap module as a possible dependency for other yet-to-be-built modules by querying PDC. During normal operation, these entries in PDC are automatically created by pdc-updater on pdc-backend02, but for the bootstrap tag they need to be manually created and linked to the new bootstrap tag.

To be usable, you’ll need a token with rights to speak to staging/prod PDC. See the PDC SOP for information on client configuration in /etc/pdc.d/ and on where to find those tokens.

Things that could go wrong

Overloading koji

If koji is overloaded, it should be acceptable to stop the fedmsg-hub daemon on mbs-backend01 at any time.

As builds finish in koji, they will be missed by the backend.. but when it restarts it should find them in datagrepper. If that fails as well, the mbs backend has a poller which should start up ~5 minutes after startup that checks koji for anything it may have missed, at which point it will resume functioning.

If koji continues to be overloaded after startup, try decreasing the NUM_CONCURRENT_BUILDS option in the config file in roles/mbs/common/templates/.