[nova][dev][ops] server status when compute host is down

Matt Riedemann mriedemos at gmail.com
Thu May 23 18:32:56 UTC 2019

On 5/22/2019 8:58 PM, melanie witt wrote:
> So, for an end user, when they do a server list, they see their server 
> as ACTIVE when it's actually powered off.

Well, it might be powered off, we don't know. If nova-compute is down 
the guest could still be running if the hypervisor is running.

> We have another field called 'host_status' available since API 
> microversion 2.16 [1] which is controlled by policy and defaults to 
> admin, which is capable of showing the server status as UNKNOWN if the 
> field is specified, for example:
> nova list --fields 
> id,name,status,task_state,power_state,networks,host_status
> This is cool, but it is only available to admin by default, and it 
> requires that the end user adds the field to their CLI command in the 
> --fields option.

As I said elsewhere in this thread, if you're proposing to add a new 
policy rule to change the 'status' field based on host_status, why not 
just tell people to open up the policy rule we already have for the 
host_status field so non-admins can see it in their server details? This 
sounds like an education problem more than a technical problem to me.

Also, --fields is one thing on one interface to the API. Microversions 
are opt-in on purpose to avoid backward incompatible and behavior 
changes to the client, so if the client has a need to know this 
information, they can opt into getting it via the host_status field by 
using the 2.16 microversion or higher. That's the case for any 
microversion that adds new fields like the embedded instance.flavor 
details in 2.47 - we didn't just say "let's add a new policy rule to 
expose those details".

> Question: do people think we should make the server status field reflect 
> UNKNOWN as well, if the 'host_status' is UNKNOWN? And if so, should it 
> be controlled by policy or no?

I'm going to vote no given we have a way to determine this already, as 
noted above.

> Normally, we do not expose compute host details to non-admin in the API 
> by default, but I noticed recently that our "down cells" support will 
> show server status as UNKNOWN if a server is in a down cell [2]. So I 
> wondered if it would be considered OK to show UNKNOWN if a host is down 
> we well, without defaulting it to admin-only.

The down-cell UNKNOWN stuff is also opt-in behavior using the 2.69 
microversion. I would likely only get behind changing the behavior of 
the 'status' field based on the compute service status in a new 
microversion, and then we have to talk about whether or not the response 
should mirror the down-cell case where we return partial results. That 
all sounds like a lot more work than just educating people about the 
host_status field and the existing policy rule to expose it.




More information about the openstack-discuss mailing list