Neutron disallows to change default enable_snat value

[Cedric Brandily]

Some deployments (private/enterprise clouds) would like to disable snat by default.
For example some enterprise policies disallow snat as it anonymizes/hides source ips and some private clouds don't use snat/nat features.

But it's currently not possible to change enable_snat default value.

A workaround is to allow and enforce neutron users to set enable_snat attribute to False on external_gateway_info update through policy, but it's not user friendly as neutron users must specify enable_snat=False and if they do not neutron returns a 404 error.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/130588
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=cf84ec4c10461bef6dd57b9645cb902e0c16584f
Submitter: Jenkins
Branch: master

commit cf84ec4c10461bef6dd57b9645cb902e0c16584f
Author: Cedric Brandily <email address hidden>
Date: Thu Oct 23 17:49:46 2014 +0200

    Allow to define enable_snat default value

    Currently neutron resets enable_snat attribute to True when enable_snat
    is not provided in router external_gateway_info. But in some deployments
    (private/enterprise clouds) such behavior is not the expected default
    one as snat/nat/floating-ips is not used (at least by default).

    This change defines the option enable_snat_by_default which allows
    deployers to set enable_snat default value when neutron resets it. The
    option default value is True for backward compatibility.

    DocImpact
    APIImpact
    Closes-Bug: #1388858
    Change-Id: I455a552230ec89fe907a087c1de8c8144b5d086e

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: neutron-pecan
Review: https://review.openstack.org/185072