[Orchagent] Recursive nexthop group enhancement

[utpalkantpintoo]

What I did

Implemented recursive nexthop group enhancement in Orchagent (NhgOrch). They have been proposed in: https://github.com/sonic-net/SONiC/pull/1636

Why I did it

These changes are required to handle a new field - "nexthop_group" in the App DB NEXT_HOP_GROUP_TABLE. Such nexthop groups are called recursive nexthop groups. This field contains the list of member (singleton) nexthop groups. Such recursive nexthop groups are represented by NEXT_HOP_GROUP objects.

How I verified it

Details if related

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• :white_check_mark: login: utpalkantpintoo / name: Utpal (ff2112ef11b13486ea2b02acf28d924f4f851c7e, 3ae044af5b3dad70031c9fe629423677e0a7bc03, 6776a5f44fcdd5f8c677fb35f3c46c22dd6f58e6, 0788fc1470a5a95059bfc2238071900be3c5ac72, fe7f488b1988cdc87d392dc149dddd9fbeaf0e37)

[utpalkantpintoo]

/azpw run Azure.sonic-swss

[mssonicbld]

/AzurePipelines run Azure.sonic-swss

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Azure Pipelines successfully started running 1 pipeline(s).

[adyeung]

@venkatmahalingam @Gokulnath-Raja pls signoff if you have no further comments

[goomadao]

Besides, there might be two issues that:

1. If a route points to a singleton NEXTHOP_GROUP and it becomes non-singleton later, the route will still refer to the SAI ID of the NEXTHOP instead of the newly created NEXTHOP_GROUP
2. For recursive situations, how to update NEXTHOP_GROUP recursively? For example, NEXTHOP_GROUP_TABLE:ID1 points to ID2 & ID3, ID2 refers to NEXTHOP NHa & NHb. When ID2 is updated to refer to NHa, NHb & NHc, how can we add member NHc to NEXTHOP_GROUP_TABLE:ID1 simultaneously?

[utpalkantpintoo]

Hi @goomadao

Thanks for the comments. Please find below my response:

1. For any nexthop-group update which changes its SAI-ID, it is expected that the routing app update the associated routes as well. This is expected behavior with FRR. Handling it in Orchagent (NhgOrch/RouteOrch) will require maintaining a nexthop-group to route entries data-structure.

2. With recursive nexthop-group scheme, it is expected that the routing app resolve the recursive nexthop-groups and provide a recursive nexthop-group with ultimate nexthop member(s) which are not recursive themselves. This is expected behavior with FRR.

[goomadao]

@utpalkantpintoo Thanks for your explanation. You're right, I missed that there is an upper application where the update could be triggered.

Could you please take a look at the pending review I raised before? I still can't figure out any situation to get into those two conditions.