incusd: Extend heartbeat data for minimum API extension count

This exposes not only the maximum API extension count as done today to
detect needed upgrades, but also the minimum value so newer servers can
restrict what they expose to clients while waiting for the cluster to be
consistent.

Signed-off-by: Stéphane Graber <stgraber@stgraber.org>

cmd/incusd/api_1.0.go

@@ -223,7 +223,7 @@ func api10Get(d *Daemon, r *http.Request) response.Response {
 	}
 
 	srv := api.ServerUntrusted{
-		APIExtensions: version.APIExtensions,
+		APIExtensions: version.APIExtensions[:d.apiExtensions],
 		APIStatus:     "stable",
 		APIVersion:    version.APIVersion,
 		Public:        false,

cmd/incusd/daemon.go

@@ -168,6 +168,9 @@ type Daemon struct {
 	// OVN clients.
 	ovnnb *ovn.NB
 	ovnsb *ovn.SB
+
+	// API info.
+	apiExtensions int
 }
 
 // DaemonConfig holds configuration values for Daemon.
@@ -197,6 +200,7 @@ func newDaemon(config *DaemonConfig, os *sys.OS) *Daemon {
 		shutdownCtx:    shutdownCtx,
 		shutdownCancel: shutdownCancel,
 		shutdownDoneCh: make(chan error),
+		apiExtensions:  len(version.APIExtensions),
 	}
 
 	d.serverCert = func() *localtls.CertInfo { return d.serverCertInt }
@@ -2384,6 +2388,10 @@ func (d *Daemon) nodeRefreshTask(heartbeatData *cluster.APIHeartbeat, isLeader b
 		return
 	}
 
+	if heartbeatData.Version.MinAPIExtensions > 0 && heartbeatData.Version.MinAPIExtensions != d.apiExtensions {
+		d.apiExtensions = heartbeatData.Version.MinAPIExtensions
+	}
+
 	// If the max version of the cluster has changed, check whether we need to upgrade.
 	if d.lastNodeList == nil || d.lastNodeList.Version.APIExtensions != heartbeatData.Version.APIExtensions || d.lastNodeList.Version.Schema != heartbeatData.Version.Schema {
 		err := cluster.MaybeUpdate(s)

internal/server/cluster/heartbeat.go

@@ -46,8 +46,9 @@ type APIHeartbeatMember struct {
 
 // APIHeartbeatVersion contains max versions for all nodes in cluster.
 type APIHeartbeatVersion struct {
-	Schema        int
-	APIExtensions int
+	Schema           int
+	APIExtensions    int
+	MinAPIExtensions int
 }
 
 // NewAPIHearbeat returns initialized APIHeartbeat.
@@ -74,7 +75,7 @@ type APIHeartbeat struct {
 // Update updates an existing APIHeartbeat struct with the raft and all node states supplied.
 // If allNodes provided is an empty set then this is considered a non-full state list.
 func (hbState *APIHeartbeat) Update(fullStateList bool, raftNodes []db.RaftNode, allNodes []db.NodeInfo, offlineThreshold time.Duration) {
-	var maxSchemaVersion, maxAPIExtensionsVersion int
+	var maxSchemaVersion, maxAPIExtensionsVersion, minAPIExtensionsVersion int
 
 	if hbState.Members == nil {
 		hbState.Members = make(map[int64]APIHeartbeatMember)
@@ -115,14 +116,19 @@ func (hbState *APIHeartbeat) Update(fullStateList bool, raftNodes []db.RaftNode,
 			maxAPIExtensionsVersion = node.APIExtensions
 		}
 
+		if minAPIExtensionsVersion == 0 || node.APIExtensions < minAPIExtensionsVersion {
+			minAPIExtensionsVersion = node.APIExtensions
+		}
+
 		if node.Schema > maxSchemaVersion {
 			maxSchemaVersion = node.Schema
 		}
 	}
 
 	hbState.Version = APIHeartbeatVersion{
-		Schema:        maxSchemaVersion,
-		APIExtensions: maxAPIExtensionsVersion,
+		Schema:           maxSchemaVersion,
+		APIExtensions:    maxAPIExtensionsVersion,
+		MinAPIExtensions: minAPIExtensionsVersion,
 	}
 
 	if len(raftNodeMap) > 0 && hbState.cluster != nil {