[MESOS-1607] Introduce optimistic offers.

• Type: Epic
• Status: Accepted
• Priority: Major
• Resolution: Unresolved
• Component/s: allocation, framework, master
• Labels: mesosphere resource-management
• Epic Name: Optimistic Offers
• Assignee: Artem Harutyunyan
• Reporter: Benjamin Hindman
• Created: 16/Jul/14 16:43
• Updated: 30/Jul/19 22:26

Description

Background
The current implementation of resource offers only enable a single framework scheduler to make scheduling decisions for some available resources at a time. In some circumstances, this is good, i.e., when we don't want other framework schedulers to have access to some resources. However, in other circumstances, there are advantages to letting multiple framework schedulers attempt to make scheduling decisions for the same allocation of resources in parallel.

If you think about this from a "concurrency control" perspective, the current implementation of resource offers is pessimistic, the resources contained within an offer are locked until the framework scheduler that they were offered to launches tasks with them or declines them. In addition to making pessimistic offers we'd like to give out optimistic offers, where the same resources are offered to multiple framework schedulers at the same time, and framework schedulers "compete" for those resources on a first-come-first-serve basis (i.e., the first to launch a task "wins"). We've always reserved the right to rescind resource offers using the 'rescind' primitive in the API, and a framework scheduler should be prepared to launch a task and have those tasks go lost because another framework already started to use those resources.

Feature
We plan to take a step towards optimistic offers, by introducing primitives that allow resources to be offered to multiple frameworks at once. At first, we will use these primitives to optimistically allocate resources that are reserved for a particular framework/role but have not been allocated by that framework/role.

The work with optimistic offers will closely resemble the existing oversubscription feature. Optimistically offered resources are likely to be considered "revocable resources" (the concept that using resources not reserved for you means you might get those resources revoked). In effect, we can may create something like a "spot" market for unused resources, driving up utilization by letting frameworks that are willing to use revocable resources run tasks.

Future Work
This ticket tracks the introduction of some aspects of optimistic offers.

Taken to the limit, one could imagine always making optimistic resource offers. This bears a striking resemblance with the Google Omega model (an isomorphism even). However, being able to configure what resources should be allocated optimistically and what resources should be allocated pessimistically gives even more control to a datacenter/cluster operator that might want to, for example, never let multiple frameworks (roles) compete for some set of resources.

Issue Links

• is related to: MESOS-6844 Avoid offer fragmentation between multiple frameworks / within a single framework.
• relates to: MESOS-4967 Oversubscription for reservation