[refactor] decouple routingServer into BGPWatcher, BGPHandler and routingHandler

[aritrbas]

Overview

• The original architecture had a monolithic routingServer with mixed responsibilities:
  • Watching BGP RIB state from GoBGP
  • Managing BGP peer configuration
  • Injecting BGP routes into VPP
  • Announcing local pod prefixes
• The refactoring splits the routingServer into three focused components:
  1. BGPWatcher – Observes GoBGP RIB state
  2. BGPHandler – Handles BGP protocol logic - RIB entries, policies, filters, defined sets, policy assignments
  3. RoutingHandler – Handles local address announcement, SNAT configuration, and route cleanup
• In addition, the architecture also involves:
  • PeerHandler – Responsible for BGP peer selection, configuration, and secret management
  • ConnectivityHandler – Manages all VPP tunnel and route programming (IPIP, VXLAN, Wireguard, IPsec, SRv6)

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Summary of Components:

1. BGPWatcher (watchers/bgp_watcher.go)

• Role: Watch the GoBGP RIB for route changes from BGP peers
• Responsibility:
  • Initializes GoBGP server with global configuration
  • Sets up initial BGP export policies (via BGPHandler)
  • Monitors the GoBGP RIB
  • Detects when peers announce or withdraw routes
  • Delegates all business logic to BGPHandler

2. BGPHandler (felix/routing/bgp_handler.go)

• Role: BGP protocol business logic and GoBGP server programming
• Responsibility:
  • Route Injection: Takes BGP paths from peers and injects routes into VPP
  • BGP Path Management: Handles path advertisements from local components
  • BGP Peer Configuration: Manages peer settings in GoBGP
  • BGP Filter Management: Translates Calico BGPFilter CRDs into GoBGP policies
  • Defined Set Management: Manages prefix lists and neighbor sets
  • Initial Policy Setup: Sets up initial BGP export policies
• Infrastructure Programmed:
  • GoBGP Server
  • VPP (indirect via RoutingHandler):
    • Routes from BGP peers (via Connectivity events)
    • SRv6 policies (via SRv6Policy events)
• Events Generated:
  • ConnectivityAdded - Route learned from BGP peer
  • ConnectivityDeleted - Route withdrawn by BGP peer
  • SRv6PolicyAdded - SRv6 tunnel route learned
  • SRv6PolicyDeleted - SRv6 tunnel route withdrawn

3. RoutingHandler (felix/routing/routing_handler.go)

• Role: Local address announcement and route cleanup
• Responsibility:
  • Local Address Advertisement: Announces pod prefixes to BGP
  • Route Cleanup: Cleans up stale routes on agent restart
  • SNAT Configuration: Configures source NAT for local traffic
• Infrastructure Programmed:
  • GoBGP Server (indirect via BGPHandler):
    • Announces local pod prefixes (via BGPPath events → BGPHandler → GoBGP server)
  • VPP:
    • SNAT configuration for local traffic
• Events Generated:
  • BGPPathAdded - Local prefix to announce
  • BGPPathDeleted - Local prefix to withdraw

4. PeerHandler (felix/routing/peer_handler.go)

• Role: BGP peer selection and configuration and secret management
• Responsibility:
  • Peer Selection: Determines which nodes to peer with
  • AS Number Management: Determines AS numbers for peers
  • Password Management: Retrieves BGP passwords from Kubernetes secrets
  • Peer Lifecycle: Manages peer add/update/delete operations
  • Secret Change Handling: Responds to secret updates
• Infrastructure Programmed:
  • GoBGP Server: (indirect via BGPHandler)
    • Updates peers (via BGPPeer events → BGPHandler → GoBGP server)
• Events Generated:
  • BGPPeerAdded - New peer to configure
  • BGPPeerUpdated - Peer configuration changed
  • BGPPeerDeleted - Peer to remove

5. ConnectivityHandler (felix/connectivity/connectivity_handler.go)

• Role: Tunnel and connectivity provider management
• Responsibility:
  • Tunnel Setup: Manages VPP tunnels based on IPAM pool configuration
  • SRv6 Policy Management: Manages SRv6 policies in VPP
  • Provider Management: Manages connectivity providers:
    • FLAT: Direct L3 routing (no encapsulation)
    • IPIP: IP-in-IP tunnel encapsulation
    • VXLAN: VXLAN overlay network
    • Wireguard: Encrypted Wireguard tunnels
    • IPsec: IPsec encrypted tunnels
    • SRv6: Segment Routing over IPv6
• Infrastructure Programmed:
  • VPP

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Event-Driven Architecture

The refactoring introduces a clean event-driven pattern:

Watcher → Event → FelixServer → Handler → Infrastructure

Event Flow

All BGP related events now flow through Felix server's event loop:

External Source (Watchers)
  → common.SendEvent()
    → felixServerEventChan
      → FelixServer.handleFelixServerEvents()
        → Handlers (BGP/Routing/Connectivity/Peer)
          → Infrastructure (GoBGP/VPP/Linux)

New Events Registered

The following events are now registered in felix_server.go and handled in handleFelixServerEvents():

common.BGPPathAdded
common.BGPPathDeleted
common.BGPPeerAdded
common.BGPPeerUpdated
common.BGPPeerDeleted
common.BGPFilterAddedOrUpdated
common.BGPFilterDeleted
common.BGPDefinedSetAdded
common.BGPDefinedSetDeleted
common.ConnectivityAdded
common.ConnectivityDeleted
common.SRv6PolicyAdded
common.SRv6PolicyDeleted
common.LocalPodAddressAdded
common.LocalPodAddressDeleted

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Separation of Watching vs Business Logic

Watching Logic (Observation)

Watcher	What It Watches	Where	Frequency
SecretWatcher	Kubernetes Secrets	K8s API	Real-time (watch)
BGPConfigurationWatcher	BGPConfiguration CRDs	Calico API	Real-time (watch)
PeerWatcher	BGPPeer CRDs	Calico API	Real-time (watch)
BGPFilterWatcher	BGPFilter CRDs	Calico API	Real-time (watch)
PrefixWatcher	IPAM prefix assignments	Calico backend	5-second poll
LocalSIDWatcher	VPP SRv6 LocalSID state	VPP API	10-second poll
BGPWatcher	GoBGP RIB changes	GoBGP stream	Real-time (gRPC)

Business Logic (Decision & Execution)

Handler	Business Logic	Programming Target
ConnectivityHandler	Tunnel setup, connectivity provider management	VPP (IPIP, VXLAN, Wireguard, IPsec, SRv6)
PeerHandler	BGP peer selection and configuration, secret management	GoBGP (peer config) [via BGPHandler]
BGPHandler	Route injection, filter policies, path management	GoBGP (RIB, policies, filters, defined sets)
RoutingHandler	Local prefix announcement, SNAT config, route cleanup	VPP (SNAT), GoBGP (announcements) [via BGPHandler]

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Made the changes on top of the abasu-peers-watcher-rem-pubsub branch for now, will rebase on top of master once those commits for single thread agent are merged.