Discovered via tempest test tempest.api.compute.servers.test_attach_interfaces.AttachInterfacesUnderV243Test.test_add_remove_fixed_ip.

This test adds SECOND fixed IP to existing VM, and then waits for it to appear in list of it's IPs (the ".../servers/uuid/ips" request).

Issue seems to be, that it's waiting for just count of IPs increasing (by exactly 1 before it consideres action to be done).
But the IP which can appear there may be Floating IP.
(The on added there during resource preparation at the beginning of test, see side-note at bottom.)

Appears at least in OSP15:
> openstack-tempest.noarch                      1:21.0.0-0.20190726140456.702b21c.el8ost                 @rhelosp-15.0-trunk                 
> python3-tempest.noarch                        1:21.0.0-0.20190726140456.702b21c.el8ost                 @rhelosp-15.0-trunk                 


There seems to be active wait-until loop, which checks the count of IPs, and in rare case tries to eliminate the floating IPs from counting (which could potentially prevent the issue).
Problem is that it goes for eliminating Floating IP's from count only in that "rare" case, when more then on IP appeared during the check.

> wait_until_+1_ip_is_there:
>   get_list_of_ips
>   if count not changed:
>     return false
>   elif count is +1:                    # this gets fullfilled by even floating IP appearing
>     return true                        # and exits here
>   filter_out_floating_ips_block_here   # this is never reached in case "just" floating poped up and not both fixed and floating at once
>   return count is +1

To me it seems could be addressed by simple fix, by just removing the first 'count is +1 => return true' part.
That way it will always go into block for eliminating floating IPs from counting.

Given that floating IPs accounting is needs more expensive requests then just list of IPs,
it could be slightly optimized by keeping also seen_ips_counter,
updated every iteration before eliminating Floating IPs.
and also doing quick exit 'return False' if count == seen_ips_counter.
That way it should do expensive request / filtering only when any new IP pops in.
(Or keep a set() of actual IPs and re-filter/evaluate when it differs from set(IPs) obtained by the first /servers/uuid/ips list.)


(Side note: it can take even about 30-40 seconds since the original Server creation from the beginning of the test,
before that Floating IP appears in the '/servers/uuid/ips' list, which happened to be in the middle of this test case, and so confusing it).