Allow overriding hostnames

README.md

@@ -239,6 +239,10 @@ When `false`, the k0s binary downloading is performed on the target host itself
 
 A path to a file on the local host that contains a k0s binary to be uploaded to the host. Can be used to test drive a custom development build of k0s.
 
+###### `spec.hosts[*].hostname` <string> (optional)
+
+Override host's hostname. When not set, the hostname reported by the operating system is used.
+
 ###### `spec.hosts[*].installFlags` <sequence> (optional)
 
 Extra flags passed to the `k0s install` command on the target host. See `k0s install --help` for a list of options.

config/cluster/host.go

@@ -30,6 +30,7 @@ type Host struct {
 	InstallFlags     Flags             `yaml:"installFlags,omitempty"`
 	Files            []UploadFile      `yaml:"files,omitempty"`
 	OSIDOverride     string            `yaml:"os,omitempty"`
+	HostnameOverride string            `yaml:"hostname,omitempty"`
 	Hooks            Hooks             `yaml:"hooks,omitempty"`
 
 	UploadBinaryPath string       `yaml:"-"`
@@ -204,6 +205,9 @@ func (h *Host) K0sInstallCommand() string {
 			extra = Flags{unQE(old)}
 		}
 		extra.AddUnlessExist(fmt.Sprintf("--node-ip=%s", h.PrivateAddress))
+		if h.HostnameOverride != "" {
+			extra.AddOrReplace(fmt.Sprintf("--hostname-override=%s", h.HostnameOverride))
+		}
 		flags.AddOrReplace(fmt.Sprintf("--kubelet-extra-args=%s", strconv.Quote(extra.Join())))
 	}
 

phase/gather_facts.go

@@ -1,6 +1,9 @@
 package phase
 
 import (
+	"fmt"
+	"strconv"
+
 	"github.com/k0sproject/k0sctl/config/cluster"
 	log "github.com/sirupsen/logrus"
 )
@@ -32,7 +35,34 @@ func (p *GatherFacts) investigateHost(h *cluster.Host) error {
 	h.Metadata.Arch = output
 	p.IncProp(h.Metadata.Arch)
 
-	h.Metadata.Hostname = h.Configurer.Hostname(h)
+	extra := h.InstallFlags.GetValue("--kubelet-extra-args")
+	if extra != "" {
+		unq, err := strconv.Unquote(extra)
+		if err != nil {
+			return err
+		}
+		ef := cluster.Flags{unq}
+		if over := ef.GetValue("--hostname-override"); over != "" {
+			unq, err = strconv.Unquote(over)
+			if err != nil {
+				return err
+			}
+			if over != "" {
+				if h.HostnameOverride != unq {
+					return fmt.Errorf("hostname and installFlags kubelet-extra-args hostname-override mismatch, only define either one")
+				}
+				h.HostnameOverride = unq
+			}
+		}
+	}
+
+	if h.HostnameOverride != "" {
+		log.Infof("%s: using %s from configuration as hostname", h, h.HostnameOverride)
+		h.Metadata.Hostname = h.HostnameOverride
+	} else {
+		h.Metadata.Hostname = h.Configurer.Hostname(h)
+		log.Infof("%s: using %s as hostname", h, h.Metadata.Hostname)
+	}
 
 	if h.PrivateAddress == "" {
 		if h.PrivateInterface == "" {