Multi-CPI Director doesn't needlessly recreate VMs #2384
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During a `bosh deploy`, a multi-CPI multi-IaaS BOSH Director may mistakenly recreate VMs that don't need to be recreated; it confuses the stemcells, thinking that the VM needs a different, wrong stemcell. This commit fixes that error by fine-tuning the stemcell selection process. Specifically, the BOSH Director uses the CPI required by the AZ that the VM is to be placed in to determine which stemcell is desired. We introduce a new method, `DeploymentPlan::InstancePlan#stemcell_model_for_cpi`, to properly select the stemcell. The source of this stemcell mismatch is from `DeploymentPlan::Stemcell#add_stemcell_models`, where the first stemcell is arbitrarily chosen from an array of stemcells, which may be the correct stemcell for some of the VMs, and the wrong stemcell for others. Although the decision to make the new method `stemcell_model_for_cpi` public is debatable (it should be a private method; it's never called outside the class), it certainly allowed for easier & more thorough testing. Fixes, from `bosh task 14721 --debug`: > D, [2022-03-08T10:29:59.075291 #14721] [] DEBUG -- DirectorJobRunner: Need to update instance 'vpn-probe/e39b63ac-fb33-4e71-bbea-61eb19b5650f (0)', changes: "stemcell" stemcell_changed? changed FROM: bosh-vsphere-esxi-ubuntu-bionic-go_agent TO: bosh-openstack-kvm-ubuntu-bionic-go_agent on instance vpn-probe/e39b63ac-fb33-4e71-bbea-61eb19b5650f (0) Drive-by: `#stemcell_changed?`: switched `@existing_instance` to `existing_instance`; if you've gone to the trouble of setting an `attr_accessor`, then you may as well take advantage it. [Fixes #2363]
beyhan
requested review from
a team,
lnguyen and
ramonskie
and removed request for
a team
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During a
bosh deploy, a multi-CPI multi-IaaS BOSH Director may mistakenly recreate VMs that don't need to be recreated; it confuses the stemcells, thinking that the VM needs a different, wrong stemcell.This commit fixes that error by fine-tuning the stemcell selection process. Specifically, the BOSH Director uses the CPI required by the AZ that the VM is to be placed in to determine which stemcell is desired.
We introduce a new method,
DeploymentPlan::InstancePlan#stemcell_model_for_cpi, to properly select the stemcell.The source of this stemcell mismatch is from
DeploymentPlan::Stemcell#add_stemcell_models, where the first stemcell is arbitrarily chosen from an array of stemcells, which may be the correct stemcell for some of the VMs, and the wrong stemcell for others.Although the decision to make the new method
stemcell_model_for_cpipublic is debatable (it should be a private method; it's never called outside the class), it certainly allowed for easier & more thorough testing.Fixes, from
bosh task 14721 --debug:[Fixes #2363]
What is this change about?
During a
bosh deploy, a multi-CPI multi-IaaS BOSH Director may mistakenly recreate VMs that don't need to be recreatedPlease provide contextual information.
#2363
What tests have you run against this PR?
Unit tests. And I've hot-patched my multi-CPI BOSH Director and have done new deploys, existing deploys, deleted deployments, uploaded stemcells, cck, etc.
How should this change be described in bosh release notes?
Multi-CPI multi-IaaS BOSH Directors no longer unnecessarily recreate VMs on deploy.
Does this PR introduce a breaking change?
No.