Turning on 'enable_dhcp' on subnet update cause request failure for pluggable IPAM

[Pavel Bondar]

Bug reproducible only if pluggable IPAM is in effect.

Steps to reproduce:
1. Enable pluggable IPAM by setting ipam_driver to 'internal' (or another ipam driver).
2. Create Network.
3. Create Subnet with unchecked 'Enable DHCP' option.
4. Verify Subnet is created.
5. Edit Subnet and check 'Enable DHCP' option, press 'Save'

Observed error in UI:
"Error: Failed to update subnet "90.90.0.0/24": No more IP addresses available on network a9bb6abf-98ec-40d3-a79f-365703949b3b."

Error in neutron log:

2015-11-10 12:07:09.656 DEBUG neutron.api.v2.base [req-c585fc85-2143-4d09-95bb-615be2fac2da admin 507df20dc0be462db98373c6bcf6a88c] Request body: {u'subnet': {u'dns_nameservers': [], u'allocation_pools': [{u'start
': u'90.90.0.2', u'end': u'90.90.0.254'}], u'host_routes': [], u'name': u'niny', u'enable_dhcp': True}} from (pid=29244) prepare_request_body /opt/stack/neutron/neutron/api/v2/base.py:645
2015-11-10 12:07:09.754 INFO neutron.api.v2.resource [req-c585fc85-2143-4d09-95bb-615be2fac2da admin 507df20dc0be462db98373c6bcf6a88c] update failed (client error): No more IP addresses available on network a9bb6a
bf-98ec-40d3-a79f-365703949b3b.

Root cause:
Query in _validate_subnet is not compatible with pluggable IPAM.
It directly queries tables for built-in IPAM.

range_qry = context.session.query(models_v2.
                        IPAvailabilityRange).join(models_v2.IPAllocationPool)

https://github.com/openstack/neutron/blob/87ce4868ca/neutron/db/db_base_plugin_v2.py#L458

Need to reword this validation to support pluggable IPAM.

[Miguel Angel Ajo (mangelajo)]

looping in Carl Baldwin to the bug.

[Miguel Angel Ajo (mangelajo)]

The report makes sense to me, needs-attention flag added for Carl to have a look on it.

[Pavel Bondar (pasha117)]

This query stands for validating subnet has at least one ip to allocate for dhcp port:

                    range_qry = context.session.query(models_v2.
                        IPAvailabilityRange).join(models_v2.IPAllocationPool)
                    ip_range = range_qry.filter_by(subnet_id=s['id']).first()
                    if not ip_range:
                        raise n_exc.IpAddressGenerationFailure(
                            net_id=cur_subnet.network_id)

But as I see there is no easy way to perform this check for third-party ipam driver.
IPAM interface allows only to allocate and deallocate ips, but info about available ips is not populated over IPAM interface.

This check was added in:
https://review.openstack.org/#/c/174228/

Need to confirm if this check is a MUST or a nice to have one.

[John Belamaric (jbelamaric)]

When is the DHCP IP address allocated? I would think that if there are no IPs left, it would produce an error at that time. If that is done synchronously, I would think it is sufficient.

Adding an IPAM call that provides a count of available addresses for a given subnet would be useful in other ways beyond this, however. But that probably wouldn't be backport-eligible since it would essentially be adding a feature.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/247019

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/247019
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=8d8444aa0ce0e6db1ebbc922311ec1eef546f2fe
Submitter: Jenkins
Branch: master

commit 8d8444aa0ce0e6db1ebbc922311ec1eef546f2fe
Author: Gary Kotton <email address hidden>
Date: Wed Nov 18 08:26:18 2015 -0800

    IPAM: fix 'enable-dhcp' with internal driver

    Commit 0c1f96ad5a6606c1205bd50ea944c3a383892cde broke the ipam
    internal driver. The base plugin should only call the ipam interface
    and not invoke the IPallocation data model.

    The code that validated that the subnet had one free IP address was
    removed. This would not guarantee that a port would indeed be free,
    that is, a parallel operation could have created a port on the subnet
    during this check.

    Closes-bug: #1514810

    Change-Id: I4d7ecb985762a8eef39cb2f22f210b4899f1a22e

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/liberty
Review: https://review.openstack.org/249060

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/249060
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=b2801195e3b3202290f55d261c89d304b2a4a0fd
Submitter: Jenkins
Branch: stable/liberty

commit b2801195e3b3202290f55d261c89d304b2a4a0fd
Author: Gary Kotton <email address hidden>
Date: Wed Nov 18 08:26:18 2015 -0800

    IPAM: fix 'enable-dhcp' with internal driver

    Commit 0c1f96ad5a6606c1205bd50ea944c3a383892cde broke the ipam
    internal driver. The base plugin should only call the ipam interface
    and not invoke the IPallocation data model.

    The code that validated that the subnet had one free IP address was
    removed. This would not guarantee that a port would indeed be free,
    that is, a parallel operation could have created a port on the subnet
    during this check.

    Closes-bug: #1514810

    Conflicts:
     neutron/db/db_base_plugin_v2.py

    Change-Id: I4d7ecb985762a8eef39cb2f22f210b4899f1a22e
    (cherry picked from commit 8d8444aa0ce0e6db1ebbc922311ec1eef546f2fe)