SwarmKit Overlay Network Integration¶

Problem¶

SwarmCracker currently implements custom VXLAN overlay, ignoring SwarmKit's built-in overlay networking.

Current behavior: - Allocates IPs locally via hash(taskID) - Creates custom VXLAN tunnels - Requires manual peer configuration

SwarmKit provides: - Centralized IPAM (IP allocation coordinated by manager) - Automatic VXLAN tunnel setup - Service discovery via DNS - Automatic peer discovery via control plane

Solution¶

Use SwarmKit overlay networks by default:

1. Respect SwarmKit-Allocated IPs¶

When NetworkAttachment.Addresses has IPs, use them instead of allocating locally:

// In createTapDevice
if len(network.Addresses) > 0 {
    // Use SwarmKit-provided IP (from overlay network IPAM)
    ipAddr = parseIPFromAddress(network.Addresses[0])
} else if nm.ipAllocator != nil {
    // Local allocation only when no SwarmKit network
    ipAddr, err = nm.ipAllocator.Allocate(taskID)
}

2. Use SwarmKit Overlay Bridge¶

SwarmKit creates bridge br-<network-id[:12]> for overlay networks. Use this bridge instead of custom VXLAN:

if network.Network.Spec.Driver == "overlay" {
    bridgeName = "br-" + network.Network.ID[:12]
}

3. Remove Custom VXLAN for Overlay¶

When using SwarmKit overlay, skip custom VXLAN setup: - SwarmKit handles VXLAN tunnel creation - SwarmKit handles FDB entries - SwarmKit handles peer discovery

Implementation Plan¶

1. Update createTapDevice:
2. Check network.Addresses first
3. Use SwarmKit-provided IP if present

4. Fall back to local allocation only for bridge networks

5. Update PrepareNetwork:

6. Skip VXLAN setup for overlay networks

7. Let SwarmKit's infrastructure handle overlay

8. Remove VXLAN flag dependency:

9. VXLAN setup only for custom bridge networks
10. Overlay networks use SwarmKit's built-in VXLAN

Testing¶

1. Create SwarmKit overlay network via API
2. Deploy services attached to overlay
3. Verify cross-node communication works
4. Verify IP allocation is coordinated by manager