Comment 34 for bug 1176046

Notes from online discussion :
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src:isc-dhcp

Trusty:

            4.2.4-7ubuntu12.8 -> (isc-dhcp-client)
            Proposal A: 4.2.4-7ubuntu12.9 -> (isc-dhcp-client, isc-dhcp-client-ddns), isc-dhcp-client Recommends: isc-dhcp-client-ddns
            Proposal B: 4.2.4-7ubuntu12.9 -> (isc-dhcp-client), patched to disable ddns if DISABLE_DDNS_LP_1176046 is set in the environment

Xenial:
            4.3.3-5ubuntu12.6 -> (isc-dhcp-client, isc-dhcp-client-ddns)
            Proposal A: 4.3.3-5ubuntu12.7 -> (isc-dhcp-client, isc-dhcp-client-ddns), isc-dhcp-client Breaks/Replaces: isc-dhcp-ddns (<< 4.3.3-5ubuntu12~)
            Proposal B: no change

Use case 1:

Trusty user has isc-dhcp-client 4.2.4-7ubuntu12.8 installed, and SRUs to end up with 4.2.4-7ubuntu12.9 of both isc-dhcp-client and isc-dhcp-client-ddns.
User upgrades to Xenial.

Expected results: user ends up with isc-dhcp-client installed but not isc-dhcp-client-ddns
Actual results in proposal A: apt resolves this by updating isc-dhcp-client-ddns first to 4.3.3-5ubuntu12.7 and then isc-dhcp-client to 4.3.3-5ubuntu12.7.
Actual results in proposal B: correct.

Use case 2:

Trusty user has isc-dhcp-client 4.2.4-7ubuntu12.8 installed, relies on ddns, and SRUs.
Expected result: ddns support still works.
Actual results in proposal A: correct.
Actual results in proposal B: correct.

Use case 3:

Trusty user has isc-dhcp-client 4.2.4-7ubuntu12.8 installed, ddns is enabled, but this breaks listening on a static UDP port as dhclient sometimes undesirably listens on it first.
Since this is already released, mandatory user intervention is acceptable
Expected result: ddns support is disabled.
Actual results in proposal A: correct with user intervention by manually removing the isc-dhcp-client-ddns package after the SRU.
Actual results in proposal B: correct, with user intervention by adding the environment setting in service startup as a conffile

User then upgrades to Xenial.
Expected results: the lack of DDNS support is still maintained.
Actual results in proposal B: correct: the environment variable is ignored.