Koschei SOP

Koschei is a continuous integration system for RPM packages. Koschei runs package scratch builds after dependency change or after time elapse and reports package buildability status to interested parties.

Contact Information

Owner

mizdebsk, msimacek

Contact

#fedora-admin

Location

Fedora Cloud

Purpose

continuous integration system

Deployment

Koschei deployment is managed by two Ansible playbooks:

sudo rbac-playbook groups/koschei-backend.yml
sudo rbac-playbook groups/koschei-web.yml

Description

Koschei is deployed on two separate machines - koschei-backend and koschei-web

Frontend (koschei-web) is a Flask WSGi application running with httpd. It displays information to users and allows editing package groups and changing priorities.

Backend (koschei-backend) consists of multiple services:

  • koschei-watcher - listens to fedmsg events for complete builds and changes build states in the database

  • koschei-repo-resolver - resolves package dependencies in given repo using hawkey and compares them with previous iteration to get a dependency diff. It resolves all packages in the newest repo available in Koji. The output is a base for scheduling new builds

  • koschei-build-resolver - resolves complete builds in the repo in which they were done in Koji. Produces the dependency differences visible in the frontend

  • koschei-scheduler - schedules new builds based on multiple criteria:

    • dependency priority - dependency changes since last build valued by their distance in the dependency graph

    • manual and static priorities - set manually in the frontend. Manual priority is reset after each build, static priority persists

    • time priority - time elapsed since the last build

  • koschei-polling - polls the same types of events as koschei-watcher without reliance on fedmsg. Additionaly takes care of package list synchronization and other regularly executed tasks

Configuration

Koschei configuration is in /etc/koschei/config-backend.cfg and /etc/koschei/config-frontend.cfg, and is merged with the default configuration in /usr/share/koschei/config.cfg (the ones in /etc overrides the defaults in /usr). Note the merge is recursive. The configuration contains all configurable items for all Koschei services and the frontend. The alterations to configuration that aren’t temporary should be done through ansible playbook. Configuration changes have no effect on already running services — they need to be restarted, which happens automatically when using the playbook.

Disk usage

Koschei doesn’t keep on disk anything that couldn’t be recreated easily - all important data is stored in PostgreSQL database, configuration is managed by Ansible, code installed by RPM and so on.

To speed up operation and reduce load on external servers, Koschei caches some data obtained from services it integrates with. Most notably, YUM repositories downloaded from Koji are kept in /var/cache/koschei/repodata. Each repository takes about 100 MB of disk space. Maximal number of repositories kept at time is controlled by cache_l2_capacity parameter in config-backend.cfg (config-backend.cfg.j2 in Ansible). If repodata cache starts to consume too much disk space, that value can be decreased - after restart, koschei-*-resolver will remove least recently used cache entries to respect configured cache capacity.

Database

Koschei needs to connect to a PostgreSQL database, other database systems are not supported. Database connection is specified in the configuration under the database_config key that can contain the following keys: username, password, host, port, database.

After an update of koschei, the database needs to be migrated to new schema. This happens automatically when using the upgrade playbook. Alternatively, it can be executed manulally using:

koschei-admin alembic upgrade head

The backend services need to be stopped during the migration.

Managing koschei services

Koschei services are systemd units managed through systemctl. They can be started and stopped independently in any order. The frontend is run using httpd.

Suspending koschei operation

For stopping builds from being scheduled, stopping the koschei-scheduler service is enough. For planned Koji outages, it’s recommended to stop koschei-scheduler. It is not necessary, as koschei can recover from Koji errors and network errors automatically, but when Koji builders are stopped, it may cause unexpected build failures that would be reported to users. Other services can be left running as they automatically restart themselves on Koji and network errors.

Limiting Koji usage

Koschei is by default limited to 30 concurrently running builds. This limit can be changed in the configuration under koji_config.max_builds key. There’s also Koji load monitoring, that prevents builds from being scheduled when Koji load is higher that certain threshold. That should prevent scheduling builds during mass rebuilds, so it’s not necessary to stop scheduling during those.

Fedmsg notifications

Koschei optionally supports sending fedmsg notifications for package state changes. The fedmsg dispatch can be turned on and off in the configuration (key fedmsg-publisher.enabled). Koschei doesn’t supply configuration for fedmsg, it lets the library to load it’s own (in /etc/fedmsg.d/).

Setting admin announcement

Koschei can display announcement in web UI. This is mostly useful to inform users about outages or other problems.

To set announcement, run as koschei user:

koschei-admin set-notice "Koschei operation is currently suspended due to scheduled Koji outage"

or:

koschei-admin set-notice "Sumbitting scratch builds by Koschei is currently disabled due to Fedora 23 mass rebuild"

To clear announcement, run as koschei user:

koschei-admin clear-notice

Adding package groups

Packages can be added to one or more group.

To add new group named mynewgroup, run as koschei user:

koschei-admin add-group mynewgroup

To add new group named mynewgroup and populate it with some packages, run as koschei user:

koschei-admin add-group mynewgroup pkg1 pkg2 pkg3

Set package static priority

Some packages are more or less important and can have higher or lower priority. Any user can change manual priority, which is reset after package is rebuilt. Admins can additionally set static priority, which is not affected by package rebuilds.

To set static priority of package foo to value 100, run as koschei user:

koschei-admin --collection f27 set-priority --static foo 100

Branching a new Fedora release

After branching occurs and Koji build targets have been created, Koschei should be updated to reflect the new state. There is a special admin command for this purpose, which takes care of copying the configuration and also last builds from the history.

To branch the collection from Fedora 27 to Fedora 28, use the following:

koschei-admin branch-collection f27 f28 -d 'Fedora 27' -t f28 --bugzilla-version 27

Then you can optionally verify that the collection configuration is correct by visiting https://apps.fedoraproject.org/koschei/collections and examining the configuration of the newly branched collection.