Scheduler Integration for System Pools

Author:Dan Callaghan, Nick Coghlan
Target Release:TBD


This proposal builds on the system pools defined in Predefined Access Policies for Systems by allowing job submitters to express preferences and requirements for system pools in their jobs.

Proposal deferral

Further work on this proposal is currently deferred, pending research into the Apache Mesos scheduling meta-framework, and its potential suitability as a replacement for the current bespoke Beaker scheduler.


As defined in Predefined Access Policies for Systems a “pool” in this proposal is a named collection of systems. Each pool has an “owning group”. Users in the owning group are allowed to add and remove systems from the pool.

The proposal described in this document allows job submitters to influence the system selection through the job XML based on a system’s pool membership.

Proposed user interface

Restrict recipe execution to a specific system pool

  • I want to submit a job and limit it to systems in a particular pool.

Through the job XML:

Use <pool op="=" value="somepool" /> in the <hostRequires/> of your job XML.

Through the bkr cli:

Pass --hostrequire=pool=somepool to a workflow command.

This filter will select only systems which are in the given pool.

Prefer particular system pools for recipe execution

  • I want to submit a job and express an ordered preference regarding the pools where I would like the job to run.

Through the job XML:

Use <autopick/> in the <recipe/> section of the job XML, with a sequence of <pool/> elements:


There is an implied “other systems” at the end, which covers all other systems which the user has access to (use <hostRequires/> to limit a job to specific system pools).

When random="true" is set on the autopick element, the pool order in the XML is still used, but the specific system used is selected randomly from within each pool (or the implied “other systems” after the list of specific pools is exhausted). To select randomly from multiple pools without expressing a preference between them, use an empty <autopick  random="true" /> element and several <pool/> selection elements grouped under a <or/> element in the <hostRequires/> section of the job XML.

Deferred features

The following additional features are under consideration, but have been deliberately omitted in order to reduce the complexity of the initial iteration of the design:

  • Allowing users to specify a default pool preference to be used when there is no autopick section in the submitted recipe XML.