On 29/10/14 09:28, Steve Baker wrote:
On 29/10/14 06:51, Steven Hardy wrote:
Hi all,
So I've been investigating bug #1383709, which has caused me to run into a
bad update pattern involving OS::Neutron::Port
http://docs.openstack.org/developer/heat/template_guide/openstack.html#OS::Neutron::Port
I'm not quite clear on the history, but for some reason, we have a
"replacement_policy" property, unlike all other resources, and it defaults
to replacing the resource every time you update, unless you pass "AUTO" to
the property.
I'm sure there's a good reason for this, but on the face of it, it seems to
be a very unsafe and inconvenient default when considering updates?
The problem (which may actually be the cause the bug #1383709) is the UUID
changes, so you don't only replace the port, you replace it and everything
that references it, which makes the Port resource a landmine of
HARestarter-esque proportions ;)
Can anyone (and in particular stevebaker who initally wrote the code) shed
any light on this? Can we just flip the default to AUTO, as it seems to be
a more desirable default for nearly all users?
Thanks!
The commit does a reasonable job of explaining the whole sorry situation
https://review.openstack.org/#/c/121693/
This was an attempt to improve port modelling enough for Juno while
nova bug #1158684 [1] remains unfixed.
If we defaulted to replacement_policy:AUTO then we have the 2 issues
when a server is replaced on stack update [3][1]
If we keep the current default then we have the symptoms of bug #1383709.
Both options suck and there is no way of always doing the right thing,
which is why replacement_policy exists - to push this decision to the
template author.
I've come to the conclusion that ports shouldn't be modelled as
resources at all; they sometimes represent exclusive resources (fixed
IPs) and their dependencies with servers sometimes goes both ways. To
fix this properly I've written a Kilo spec for blueprint
rich-network-prop [2]
Before we switch the default to AUTO maybe we could investigate
getting REPLACE_ALWAYS to interact better with ResourceGroup (or the
tripleo templates which use it)
I've looked at the tripleo templates now, and they create ports which
are resources in their own right, so switching to
replacement_policy:AUTO is entirely appropriate. However in most
templates the vast majority of port resources are just to define a
simple server/port/floating-IP combo. Therefore I think there is a good
argument for the default REPLACE_ALWAYS causing the least problems for
the majority of cases.
[1] https://bugs.launchpad.net/nova/+bug/1158684
[2] https://review.openstack.org/#/c/130093/
[3] https://bugs.launchpad.net/heat/+bug/1301486
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