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[nova] [horizon] Horizon and nova-cli inconsistency in live migration parameters


On 7/14/2019 7:35 AM, Mary Atakova wrote:
> I try to live-migrate a VM, and I do it through nova cli and through 
> Horizon, and nova-api logs contain different data depending on the way I 
> do it.
> 
> 1. nova cli
> 
> I run the command:
> 
> nova live-migration 17359460-d23c-4acc-a9b1-5cf117b54430
> 
> and it shows up in nova-api logs as:
> 
> {"os-migrateLive": {"block_migration": "auto", "host": null}}
> 
> 2. horizon
> 
> I run live migration via Horizon with unchecked Disk Overcommit and 
> unchecked Block Migration.
> 
> It shows up in nova-api logs as:
> 
> {"os-migrateLive": {"disk_over_commit": false, "block_migration": false, 
> "host": null}}
> 
> This difference can lead to different parameters provided for live 
> migration when block_migration: auto is translated into block_migration: 
> true.

The difference is in the compute API microversion used. The nova CLI by 
default negotiates the highest microversion to use between what the 
client understands and what the server provides. The 'auto' value for 
the block_migration parameter was added in 2.25 and disk_over_commit was 
removed in 2.25. Horizon is likely not specifying a specific 
microversion so it defaults to 2.1 and that's why you're getting 
"disk_over_commit": false, "block_migration": false because you 
unchecked those check boxes.

In other words, for Horizon to support compute API 2.25 there would be 
an "Auto" option for the Block Migration value.

-- 

Thanks,

Matt