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