On Demand Compose Service SOP

The ODCS is very new and changing rapidly. We’ll try to keep this up to date as best we can.

The ODCS is a service generating temporary compose from Koji tag(s) using Pungi.

Contact Information


Factory2 Team, Release Engineering Team, Infrastructure Team


#fedora-modularity, #fedora-admin, #fedora-releng


jkaluza, cqi, qwan, threebean

Public addresses
  • odcs.fedoraproject.org

  • odcs-frontend0[1-2].iad2.fedoraproject.org

  • odcs-backend01.iad2.fedoraproject.org


Generate temporary compose from Koji tag(s) using Pungi.


ODCS clients submit request for a compose to odcs.fedoraproject.org. The requests are submitted using python2-odcs-client Python module or just using plain JSON.

The request contains all the information needed to build a compose:

  • source type: Type of compose source, for example "tag" or "module"

  • source: Name of Koji tag or list of modules defined by name-stream-version.

  • packages: List of packages to include in a compose.

  • seconds to live: Number of seconds after which the compose is removed from the filesystem and is marked as "removed".

  • flags: Various flags further defining the compose - for example the "no_deps" flag saying that the packages dependencies should not be included in a compose.

The request is received by the ODCS flask app running on odcs-frontend nodes. The frontend does input validation of the request and then adds the compose request to database with "wait" state and sends fedmsg message about this event. The compose request gets its unique id which can be used by a client to query its status using frontend REST API.

The odcs-backend node then handles the compose requests in "wait" state and starts generating the compose using the Pungi tool. It does so by generating all the configuration files for Pungi and executing "pungi" executable. Backend also changes the compose request status to "generating" and sends fedmsg message about this event.

The number of concurrent pungi processes can be set using the num_concurrent_pungi variable in ODCS configuration file.

The output directory for a compose is shared between frontend and backend node. Once the compose is generated, the backend changes the status of compose request to "done" and again sends fedmsg message about this event.

The shared directory with a compose is available using httpd on the frontend node and ODCS client can access the generated compose. By default this is on https://odcs.fedoraproject.org/composes/ URL.

If the compose generation goes wrong, the backend changes the state of the compose request to "failed" and again sends fedmsg message about this event. The "failed" compose is still available for seconds to live time in the shared directory for further examination of pungi logs if needed.

After the seconds to live time, the backend node removes the compose from filesystem and changes the state of compose request to "removed".

If there are compose requests for the very same composes, the ODCS will reuse older compose instead of generating new one and points the new compose to older one.

The "removed" compose can be renewed by a client to generate the same compose as in the past. The seconds to live attribute of a compose can be extended by a client when needed.

Observing ODCS Behavior

There is currently no command line tool to query ODCS, but ODCS provides REST API which can be used to observe the ODCS behavior. This is available on https://odcs.fedoraproject.org/api/1/composes.

The API can be filtered by following keys entered as HTTP GET variables:

  • owner

  • source_type

  • source

  • state

It is also possible to see all the current composes in the compose output directory, which is available on the frontend on https://odcs.fedoraproject.org/composes.

Removing compose before its expiration time

Members of FAS group defined in the admins section of ODCS configuration can remove any compose by sending DELETE request to following URL:


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

The backend logs are on odcs-backend01. Look in the journal for the odcs-backend service.


The package in question is odcs-server. Please use the playbooks/manual/upgrade/odcs.yml playbook.

Things that could go wrong

Not enough space on shared volume

In case there are too many composes, member of FAS group defined in the ODCS configuration file admins section should:

  • Remove the oldest composes to get some free space immediatelly. List of such composes can be found on https://odcs.fedoraproject.org/composes/ by sorting by Last modified fields.

  • Decrease the max_seconds_to_live in ODCS configuration file.