chore: add multi VPC attachment test

[pau-hedgehog]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for testing multi-VPC attachments in the testing framework. It enables servers to be attached to multiple VPCs simultaneously using a primary+next pattern for VPC selection.

Key changes:

• Added multi-VPC server selection logic that chooses servers by connection type (unbundled, bundled, mclag, eslag)
• Modified VPC attachment creation to support multiple attachments per server with proper naming
• Updated connectivity testing to test all attachment combinations between servers

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
pkg/hhfab/testing.go	Main implementation of multi-VPC attachment logic, modified VPC setup and connectivity testing
pkg/hhfab/hhnet.sh	Added addvlan command to support adding VLANs to existing bonds
cmd/hhfab/main.go	Added CLI flag --servers-with-multi-vpc to control the feature

[Copilot]

The edge case handling for wraparound when currentVPCID equals vpcID could be simplified. Consider using a while loop to ensure we always get a different VPC ID rather than hardcoding the +2 offset.

Suggested change

	// If wraparound results in same VPC (edge case with single VPC), skip to avoid duplicate
	if currentVPCID == vpcID && totalVPCs > 1 {
	currentVPCID = (vpcID + 2) % totalVPCs
	// If wraparound results in same VPC, increment until different (avoids duplicate)
	for currentVPCID == vpcID && totalVPCs > 1 {
	currentVPCID = (currentVPCID + 1) % totalVPCs

[Copilot]

The interface name format "bond0.%d" is hardcoded in multiple places. Consider defining it as a constant to improve maintainability.

Suggested change

	sourceInterface := fmt.Sprintf("bond0.%d", attachA.VLAN)
	sourceInterface := fmt.Sprintf(BondInterfaceFormat, attachA.VLAN)

[Copilot]

The iperf3 -B flag expects an IP address or interface name, but sourceInterface contains a VLAN interface name (e.g., "bond0.1000"). This may not work correctly with iperf3. Consider using the IP address of the interface instead.

Suggested change

	cmd += fmt.Sprintf(" -B %s", sourceInterface)
	bindAddr := sourceInterface
	// If sourceInterface looks like an interface name (not an IP), resolve to IP
	if netip.ParseAddr(sourceInterface).IsValid() == false {
	ip, err := getInterfaceIP(sourceInterface)
	if err != nil {
	return fmt.Errorf("could not resolve IP for interface %q: %w", sourceInterface, err)
	}
	bindAddr = ip
	}
	cmd += fmt.Sprintf(" -B %s", bindAddr)

[Copilot]

The interface name format "bond0.%d" is duplicated again. This reinforces the need for a constant to avoid inconsistencies.

Suggested change

	sourceInterface := fmt.Sprintf("bond0.%d", attach.VLAN)
	sourceInterface := fmt.Sprintf(BondInterfaceFormat, attach.VLAN)

[Frostman]

I think we shouldn't be doing it now, there are too many things to do:

• SetupVPCs is already overloaded, and to make it properly configurable, it would be difficult w/o rewriting and introducing some kind of simple lang to define VPCs (similar to the peerings)
• We cannot rely on bond0 - what if you have multiple multihomed connections at the same time
• We should calculate source interface for pings/iperfs/curls very carefully and it technically could be a list to test, not just a single one
• When we're doing multi-attach to servers we would need to test all permutations - check connectivity from all attachments of all servers to all attachments of all servers to make sure that traffic will not go through where we don't expect it