rotate: narrow a pair credential to one consuming module (hq issue 268)

A machine runs many consumers of one provision, each with its own
credential. When one module leaks its credential, `rotate <provision>
--consumer <machine>` was the narrowest act and replaced every module's
on that machine, restarting all of them. --module (and the verb's
module argument beside provision) rotates only that module's.

cmd/mesh-controller/main.go

@@ -232,7 +232,7 @@ func usage() {
   licence add|list|use|key       model access, under the name a person calls it
   licence manager <name> <node>  the node that holds a refreshable licence's refresh token
   licence refresh <name>         mint a new access token and seal it to every holder
-  rotate <provision> [--consumer <n>]  a new credential for every holder, both ends at once
+  rotate <provision> [--consumer <n>] [--module <m>]  a new credential for every holder, both ends at once
   ask <module> <tool> [json]           call one of a module's tools over the broker, and print its answer
   pin <node> <provision> <from-node> <module>
                                  which provider this one gets a provision from: the module, and its node

cmd/mesh-controller/rotate.go

@@ -6,6 +6,8 @@ import (
 	"flag"
 	"fmt"
 	"sort"
+
+	"github.com/novox/mesh-controller/internal/inventory"
 )
 
 // rotateCommand replaces a credential and moves both ends together.
@@ -33,12 +35,16 @@ func rotateCommand(ctx context.Context, args []string) error {
 	// One consumer rather than all of them. Ordinary: a credential is suspected on one machine,
 	// and rotating the other nine would be a great deal of disruption for one suspicion.
 	only := set.String("consumer", "", "only this machine's credential, rather than every holder's")
+	// One consuming module rather than every module on the machine. A machine runs many consumers
+	// of one provision, each with its own credential; one module that leaked its credential (novox/hq
+	// issue 268) is no reason to restart every other one on the machine.
+	module := set.String("module", "", "only this consuming module's credential")
 	positionals, err := parseAround(set, args)
 	if err != nil {
 		return err
 	}
 	if len(positionals) != 1 {
-		return errors.New("rotate <provision> [--consumer <machine>]")
+		return errors.New("rotate <provision> [--consumer <machine>] [--module <module>]")
 	}
 	provision := positionals[0]
 
@@ -53,6 +59,12 @@ func rotateCommand(ctx context.Context, args []string) error {
 	if err != nil {
 		return err
 	}
+	holders = ofModule(holders, *module)
+	if len(holders) == 0 && *module != "" {
+		return fmt.Errorf(
+			"no module %s%s holds a credential for %q, so there is nothing to rotate. `plan <machine>` "+
+				"says what a machine holds", *module, onMachine(*only), provision)
+	}
 	if len(holders) == 0 {
 		// Said, not silent. "Nobody holds this" and "this did not run" must never look the same —
 		// and a rotation somebody believes happened is worse than one they know did not.
@@ -116,6 +128,27 @@ func rotateCommand(ctx context.Context, args []string) error {
 	return nil
 }
 
+// ofModule is the holders whose consuming module is this one; all of them when none is named.
+func ofModule(holders []inventory.Holder, module string) []inventory.Holder {
+	if module == "" {
+		return holders
+	}
+	var out []inventory.Holder
+	for _, h := range holders {
+		if h.ConsumerModule == module {
+			out = append(out, h)
+		}
+	}
+	return out
+}
+
+func onMachine(machine string) string {
+	if machine == "" {
+		return ""
+	}
+	return " on " + machine
+}
+
 // asLocal names the credential inside the consumer where it holds several (ADR 0094).
 func asLocal(local string) string {
 	if local == "" {

cmd/mesh-controller/rotate_test.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// One consuming module's credential, and not its neighbours' on the same machine (novox/hq issue
+// 268): a module that leaked its database password is no reason to restart every other consumer.
+func TestARotationNarrowedToAModuleTouchesOnlyThatModulesCredential(t *testing.T) {
+	holders := []inventory.Holder{
+		{Provision: "postgres-database", Consumer: "ace", ConsumerModule: "letta", Provider: "ace"},
+		{Provision: "postgres-database", Consumer: "ace", ConsumerModule: "n8n", Provider: "ace"},
+		{Provision: "postgres-database", Consumer: "ace", ConsumerModule: "letta", Local: "reader", Provider: "ace"},
+	}
+	got := ofModule(holders, "letta")
+	if len(got) != 2 || got[0].ConsumerModule != "letta" || got[1].Local != "reader" {
+		t.Fatalf("narrowed to letta: %+v", got)
+	}
+	if len(ofModule(holders, "")) != 3 {
+		t.Fatal("no module named narrowed anyway")
+	}
+	if len(ofModule(holders, "absent")) != 0 {
+		t.Fatal("a module holding nothing matched")
+	}
+}

cmd/mesh-controller/seatverbs.go

@@ -371,6 +371,11 @@ func (a *verbArguments) commandLine() ([]string, error) {
 			if c := str("consumer"); c != "" {
 				argv = append(argv, "--consumer", c)
 			}
+			// With a provision, module narrows to one consuming module (novox/hq issue 268); node
+			// and secret stay the other shape's, and are refused as passed over.
+			if m := str("module"); m != "" {
+				argv = append(argv, "--module", m)
+			}
 			return argv, nil
 		}
 		_, node := a.given["node"]

cmd/mesh-controller/seatverbs_test.go

@@ -43,6 +43,10 @@ func TestRotateTakesAProvisionOrAnOwnSecret(t *testing.T) {
 	if strings.Join(argv, " ") != "rotate postgres-database --consumer ace" {
 		t.Fatalf("a pair credential: %v", argv)
 	}
+	argv, _ = argvFor("rotate", map[string]any{"provision": "postgres-database", "consumer": "ace", "module": "letta"})
+	if strings.Join(argv, " ") != "rotate postgres-database --consumer ace --module letta" {
+		t.Fatalf("one consuming module's pair credential: %v", argv)
+	}
 	argv, _ = argvFor("rotate", map[string]any{"node": "ace", "module": "nodered", "secret": "api-token"})
 	if strings.Join(argv, " ") != "secret rotate ace nodered api-token" {
 		t.Fatalf("an own secret: %v", argv)

internal/catalogue/verbs.go

@@ -142,7 +142,7 @@ var ControllerVerbs = []Verb{
 			"node":   "the machine's name; without it, every machine that is behind",
 			"behind": "\"true\": every machine that is behind, the whole mesh — the same as naming none, said outright; not with node",
 		}, nil, "behind")},
-	{Name: "rotate", Description: "Replace a credential. A pair credential, by provision (and a consuming machine, " +
+	{Name: "rotate", Description: "Replace a credential. A pair credential, by provision (and a consuming machine and module, " +
 		"else every holder): both ends are re-sent together. Or a module's own secret, by machine, module and " +
 		"name: made anew and the machine sent, so the module starts again on it — only for a secret its " +
 		"definition says it reads at start; a value given to the mesh, or one the module applies to a backend, is refused with the reason.",
@@ -150,7 +150,7 @@ var ControllerVerbs = []Verb{
 			"provision": "a pair credential: the provision whose credential to replace",
 			"consumer":  "with provision: only the holder on this machine (optional)",
 			"node":      "an own secret: the machine",
-			"module":    "an own secret: the module",
+			"module":    "an own secret: the module; with provision: only this consuming module's credential (optional)",
 			"secret":    "an own secret: its name in the module's definition",
 		}, nil)},
 	{Name: "issue", Description: "Give a module on a machine its account on the bus: minted, and sealed to the " +