[bgp] Re-add dependency in managers_bgp for bgpcfgd

[yaqiangz]

Why I did it

These 2 dependencies were removed by #18764 and #18727 for decoupling hard dependency between Loopback IPv4 address and BGP.
Actually, these dependencies are to make sure existence of Loopback interface, no need to remove.

Work item tracking

• Microsoft ADO (number only): 28210625

How I did it

Add dependency back

How to verify it

UT passed.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[yaqiangz]

/azpw ms_conflict

[StormLiangMS]

hi @yaqiangz I remember you mentioned this interface would be monitored in the bgp manager file? why we need to add these two back?

[StormLiangMS]

hi @yaqiangz I remember you mentioned this interface would be monitored in the bgp manager file? why we need to add these two back?

src/sonic-bgpcfgd/bgpcfgd/main.py

[yaqiangz]

hi @yaqiangz I remember you mentioned this interface would be monitored in the bgp manager file? why we need to add these two back?

@StormLiangMS Yes interface change will be monitored by https://github.com/sonic-net/sonic-buildimage/blob/master/src/sonic-bgpcfgd/bgpcfgd/main.py#L50

The dependency is to make sure Loopback interface exist. With this dependency adding:
If interested table changed, but CONFIG_DB entry LOOPBACK_INTERFACE|Loopback0 doesn't exist, it will not invoke handler for the table change, but record it until the entry LOOPBACK_INTERFACE|Loopback0 appear.

I removed them previously because I thought these dependencies require LOOPBACK_INTERFACE|Loopback0|<ipv4_address> should always exist, which would make bgp cannot work well in Loopback IPv6 only scenario. But actually these dependencies require LOOPBACK_INTERFACE|Loopback0 should always exist, it treats Loopback interface existence as a must have for SONiC BGP, I think it's reasonable to have it, so added them back

[StormLiangMS]

After discussion, if we configured IPv6 or IPv4 on the loopback interface, it will create LOOPBACK_INTERFACE|Loopback0 in the config_db, no matter a IPv6 or IPv4 addressed configured. In previous assumption, the device could be IPv6 only later, and in either case, there should at least one of them (IPv6 or IPv4) available, no harm to add the dependency on LOOPBACK_INTERFACE|Loopback0 back.

[StormLiangMS]

LGTM.

[bingwang-ms]

Hi @yaqiangz , @StormLiangMS Is this change required for 202405 branch?

[yaqiangz]

Hi @yaqiangz , @StormLiangMS Is this change required for 202405 branch?

Hi @bingwang-ms it's included in 202405 by this commit d1875c6