| 2020-04-01 11:48:07 |
Johannes Kulik |
description |
Description
===========
When using soft-affinity to schedule instances on the same host, the weight is unexpectedly low if a server was previously scheduled to any server-group with more members on a host.
Steps to reproduce
==================
Do not restart nova-scheduler in the process or the bug doesn't appear.
* Create a server-group with soft-affinity (let's call it A)
* Create 6 servers in server-group A, one after the other so they end up on the same host.
* Create another server-group with soft-affinity (B)
* Create 1 server in server-group B
* Create 1 server in server-group B and look at the scheduler's weights assigned to the hosts by the ServerGroupSoftAffinityWeigher.
Expected result
===============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher should be 1, as the maximum number of instances for server-group B is on that host (the one we created there before).
Actual result
=============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher is 0.2, as the maximum number of instances ever encountered on a host is 5.
Environment
===========
We noticed this on a queens version of nova a year ago. Can't give the exact commit anymore, but the code still looks broken in current master.
I've opened a review-request for fixing this bug here: https://review.opendev.org/#/c/713863/ |
Description
===========
When using soft-affinity to schedule instances on the same host, the weight is unexpectedly low if a server was previously scheduled to any server-group with more members on a host. This low weight can then be easily outweighed by differences in resources (e.g. RAM/CPU).
Steps to reproduce
==================
Do not restart nova-scheduler in the process or the bug doesn't appear. You need to change the ServerGroupSoftAffinityWeigher to actually log the weights it computes to see the problem.
* Create a server-group with soft-affinity (let's call it A)
* Create 6 servers in server-group A, one after the other so they end up on the same host.
* Create another server-group with soft-affinity (B)
* Create 1 server in server-group B
* Create 1 server in server-group B and look at the scheduler's weights assigned to the hosts by the ServerGroupSoftAffinityWeigher.
Expected result
===============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher should be 1, as the maximum number of instances for server-group B is on that host (the one we created there before).
Actual result
=============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher is 0.2, as the maximum number of instances ever encountered on a host is 5.
Environment
===========
We noticed this on a queens version of nova a year ago. Can't give the exact commit anymore, but the code still looks broken in current master.
I've opened a review-request for fixing this bug here: https://review.opendev.org/#/c/713863/ |
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