Give each overlay container its own designated IP from the band

Instead of all containers trying the same candidate list and competing
(causing allocation failures), each container now gets only its specific
IP based on its overlay index within the config.

Author: firecow

main.go

@@ -220,6 +220,7 @@ func (m *manager) run(config *Config) {
 	}
 	m.l.WithField("networks", networkNames).Debugf("Networks: %s", networkNames)
 
+	overlayIndex := 0
 	for _, c := range config.Containers {
 
 		var networks []string = nil
@@ -229,14 +230,19 @@ func (m *manager) run(config *Config) {
 		}
 		networks = lo.Ternary(len(networks) > 0, networks, []string{"bridge"})
 
-		err = m.ensureContainer(c, networks)
+		currentIndex := overlayIndex
+		if c.AttachAllNetwork {
+			overlayIndex++
+		}
+
+		err = m.ensureContainer(c, networks, currentIndex)
 		if err != nil {
 			m.l.WithField("name", c.Name).WithError(err).Errorf("failed to enure container %s", c.Name)
 		}
 	}
 }
 
-func (m *manager) ensureContainer(config Container, networks []string) error {
+func (m *manager) ensureContainer(config Container, networks []string, overlayIndex int) error {
 	containers, err := m.cli.ContainerList(m.ctx, container.ListOptions{All: true, Filters: filters.NewArgs(filters.Arg("name", fmt.Sprintf("^/%s$", config.Name)))})
 	if err != nil {
 		return err
@@ -282,7 +288,7 @@ func (m *manager) ensureContainer(config Container, networks []string) error {
 					return e.Name == config.Name
 				})
 				if !alreadyAttached {
-					m.connectNetworkHighIP(n, config.Name, config.Name)
+					m.connectNetworkHighIP(n, config.Name, config.Name, overlayIndex)
 				}
 			}
 
@@ -409,7 +415,7 @@ func (m *manager) ensureContainer(config Container, networks []string) error {
 		// Connect networks after start so overlay handshakes happen immediately
 		// and NetworkConnect returns the real error on IP conflict
 		for _, n := range networks {
-			m.connectNetworkHighIP(n, c.ID, config.Name)
+			m.connectNetworkHighIP(n, c.ID, config.Name, overlayIndex)
 		}
 
 		return nil
@@ -509,8 +515,8 @@ func (m *manager) detachNetwork(network string, container string) {
 // connectNetworkHighIP connects a container to a network using an IP from the
 // upper end of the subnet. If the chosen IP conflicts, it falls back to
 // Docker-assigned.
-func (m *manager) connectNetworkHighIP(networkName string, containerID string, containerName string) {
-	candidates := m.highIPCandidates(networkName)
+func (m *manager) connectNetworkHighIP(networkName string, containerID string, containerName string, overlayIndex int) {
+	candidates := m.highIPCandidates(networkName, overlayIndex)
 	if candidates == nil {
 		err := m.cli.NetworkConnect(m.ctx, networkName, containerID, nil)
 		if err != nil {
@@ -542,7 +548,7 @@ func (m *manager) connectNetworkHighIP(networkName string, containerID string, c
 
 // highIPCandidates returns IPs from a tight band at the top of the network's
 // subnet, using the overlay Peers list for deterministic per-node positioning.
-func (m *manager) highIPCandidates(networkName string) []net.IP {
+func (m *manager) highIPCandidates(networkName string, overlayIndex int) []net.IP {
 	networkInfo, err := m.cli.NetworkInspect(m.ctx, networkName, types.NetworkInspectOptions{})
 	if err != nil {
 		return nil
@@ -574,7 +580,11 @@ func (m *manager) highIPCandidates(networkName string) []net.IP {
 		peerIPs[i] = p.IP
 	}
 
-	return computeIPCandidates(ipNet, peerIPs, m.nodeAddr, m.overlayContainers)
+	candidates := computeIPCandidates(ipNet, peerIPs, m.nodeAddr, m.overlayContainers)
+	if overlayIndex >= len(candidates) {
+		return nil
+	}
+	return []net.IP{candidates[overlayIndex]}
 }
 
 func computeIPCandidates(ipNet *net.IPNet, peerIPs []string, nodeAddr string, overlayContainers int) []net.IP {