Change RKE upgrade logic for zero downtime

cluster/validation.go

@@ -3,14 +3,14 @@ package cluster
 import (
 	"context"
 	"fmt"
-	"github.com/rancher/rke/metadata"
-	"k8s.io/api/core/v1"
 	"strings"
 
 	"github.com/rancher/rke/log"
+	"github.com/rancher/rke/metadata"
 	"github.com/rancher/rke/pki"
 	"github.com/rancher/rke/services"
 	"github.com/rancher/rke/util"
+	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/util/validation"
 )
 
@@ -196,6 +196,39 @@ func ValidateHostCount(c *Cluster) error {
 	return nil
 }
 
+func (c *Cluster) ValidateHostCountForUpgrade() error {
+	var inactiveControlPlaneHosts, inactiveWorkerOnlyHosts []string
+	var workerOnlyHosts int
+	for _, host := range c.InactiveHosts {
+		if host.IsControl {
+			inactiveControlPlaneHosts = append(inactiveControlPlaneHosts, host.HostnameOverride)
+		}
+		if !host.IsEtcd && !host.IsControl {
+			inactiveWorkerOnlyHosts = append(inactiveWorkerOnlyHosts, host.HostnameOverride)
+		}
+		// not breaking out of the loop so we can log all of the inactive hosts
+	}
+	if len(inactiveControlPlaneHosts) >= 1 {
+		return fmt.Errorf("cannot proceed with upgrade of controlplane if one or more controlplane hosts are inactive; found inactive hosts: %v", strings.Join(inactiveControlPlaneHosts, ","))
+	}
+
+	for _, host := range c.WorkerHosts {
+		if host.IsControl || host.IsEtcd {
+			continue
+		}
+		workerOnlyHosts++
+	}
+
+	maxUnavailable, err := services.CalculateMaxUnavailable(c.UpgradeStrategy.MaxUnavailable, workerOnlyHosts)
+	if err != nil {
+		return err
+	}
+	if len(inactiveWorkerOnlyHosts) >= maxUnavailable {
+		return fmt.Errorf("cannot proceed with upgrade of worker components since %v (>=maxUnavailable) hosts are inactive; found inactive hosts: %v", len(inactiveWorkerOnlyHosts), strings.Join(inactiveWorkerOnlyHosts, ","))
+	}
+	return nil
+}
+
 func validateDuplicateNodes(c *Cluster) error {
 	for i := range c.Nodes {
 		for j := range c.Nodes {