server add records the floating address where the summary can read it

keepalived's file holds its password and is root's alone; the control plane
runs as llmgw and could not read it, so the CONTROL line never named the
floating address.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/cli/controlplanes.go

@@ -1,7 +1,6 @@
 package cli
 
 import (
-	"bufio"
 	"context"
 	"net"
 	"net/http"
@@ -15,8 +14,8 @@ import (
 	"gitea.mynodes.xyz/ilker/llmgw/internal/store"
 )
 
-// keepalivedPath is where `server add --vip` writes the floating address.
-const keepalivedPath = "/etc/keepalived/keepalived.conf"
+// floatingPath is where `server add --vip` records the floating address.
+const floatingPath = "/etc/llmgw/floating"
 
 // controlPlaneProbe answers the summary's question of which control plane
 // leads: it asks each one's /leader, on the client port every one of them
@@ -46,7 +45,7 @@ func newControlPlaneProbe(st *store.DB, listen string) *controlPlaneProbe {
 	self, _ := os.Hostname()
 	return &controlPlaneProbe{st: st, self: self,
 		leaderURL: func(host string) string { return "http://" + net.JoinHostPort(host, port) + "/leader" },
-		floating:  floatingAddress(keepalivedPath),
+		floating:  floatingAddress(floatingPath),
 		client:    &http.Client{Timeout: time.Second}}
 }
 
@@ -104,30 +103,18 @@ func (p *controlPlaneProbe) ask(ctx context.Context, host string) string {
 	return "not answering"
 }
 
-// floatingAddress is the address in the keepalived configuration server add
-// wrote, without its prefix; "" when there is none, or the file is someone
-// else's.
+// floatingAddress is the address in the file server add keeps beside the
+// keepalived configuration, without its prefix; "" when nothing floats.
+// keepalived's own file holds its password and is root's alone, and this
+// process is not root.
 func floatingAddress(path string) string {
-	f, err := os.Open(path) //nolint:gosec // a fixed system path
+	b, err := os.ReadFile(path) //nolint:gosec // a fixed path of our own
 	if err != nil {
 		return ""
 	}
-	defer f.Close()
-	sc := bufio.NewScanner(f)
-	ours, in := false, false
-	for sc.Scan() {
-		line := strings.TrimSpace(sc.Text())
-		switch {
-		case strings.HasPrefix(line, "# llmgw:"):
-			ours = true
-		case strings.HasPrefix(line, "virtual_ipaddress"):
-			in = true
-		case in && line == "}":
-			return ""
-		case in && ours && line != "":
-			addr, _, _ := strings.Cut(strings.Fields(line)[0], "/")
-			return addr
-		}
+	addr, _, _ := strings.Cut(strings.TrimSpace(string(b)), "/")
+	if net.ParseIP(addr) == nil {
+		return ""
 	}
-	return ""
+	return addr
 }

internal/cli/controlplanes_test.go

@@ -111,19 +111,18 @@ func TestOneControlPlaneIsNotASetOfThem(t *testing.T) {
 
 func TestTheFloatingAddressIsReadFromWhatServerAddWrote(t *testing.T) {
 	dir := t.TempDir()
-	ours := filepath.Join(dir, "ours.conf")
-	if err := os.WriteFile(ours, []byte(keepalivedConf("eth0", "10.0.0.161", 24, 110, "abcd1234")), 0o600); err != nil {
+	file := filepath.Join(dir, "floating")
+	if err := os.WriteFile(file, []byte("10.0.0.161/24\n"), 0o644); err != nil {
 		t.Fatal(err)
 	}
-	if got := floatingAddress(ours); got != "10.0.0.161" {
+	if got := floatingAddress(file); got != "10.0.0.161" {
 		t.Errorf("read %q", got)
 	}
-	theirs := filepath.Join(dir, "theirs.conf")
-	if err := os.WriteFile(theirs, []byte("vrrp_instance x {\n  virtual_ipaddress {\n    10.9.9.9/24\n  }\n}\n"), 0o600); err != nil {
+	if err := os.WriteFile(file, []byte("not an address\n"), 0o644); err != nil {
 		t.Fatal(err)
 	}
-	if got := floatingAddress(theirs); got != "" {
-		t.Errorf("someone else's keepalived read as ours: %q", got)
+	if got := floatingAddress(file); got != "" {
+		t.Errorf("nonsense read as %q", got)
 	}
 	if got := floatingAddress(filepath.Join(dir, "none")); got != "" {
 		t.Errorf("no file read as %q", got)

internal/cli/serveradd.go

@@ -489,6 +489,12 @@ sudo systemctl restart keepalived`, []byte(conf)); err != nil {
 			return fmt.Errorf("on %s: %v: %s", m.name, err, strings.TrimSpace(string(out)))
 		}
 	}
+	// Where the summary reads it, on both: readable, unlike keepalived's.
+	for _, r := range []onboard.Remote{here, sa.remote} {
+		if out, err := r.Run(ctx, "sudo sh -c 'cat > "+floatingPath+" && chmod 0644 "+floatingPath+"'", []byte(sa.vip+"\n")); err != nil {
+			return fmt.Errorf("recording it: %v: %s", err, strings.TrimSpace(string(out)))
+		}
+	}
 	sa.done("%s follows whichever control plane leads (keepalived on both)", sa.vip)
 	return nil
 }