cmd/mesh-controller/push.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -690,6 +691,39 @@ func sendTo(ctx context.Context, open *stores, names []string) error {
 		}
 		fmt.Printf("  sent %s %d resource(s)\n", s.node, len(s.declared.Resources))
 	}
+	// And every assignment on those machines its membership (novox/hq ADR 0160): composed from the
+	// same records the bus's accounts are, so what a runtime serves and what its account may are one
+	// composition. Issued after the declaration, because the runtime it is for arrives with it.
+	return issueMemberships(ctx, open, server, names)
+}
+
+// issueMemberships publishes the membership of every module on the named machines.
+func issueMemberships(ctx context.Context, open *stores, server *link.Server, names []string) error {
+	records, err := open.inventory.BusRecords(ctx)
+	if err != nil {
+		return err
+	}
+	where := broker.PlacementsOf(records, records.Interchangeable)
+	bus, ok := server.Bus().(link.OverNATS)
+	if !ok {
+		return nil
+	}
+	issued := 0
+	for _, node := range names {
+		for _, d := range records.Assigned[node] {
+			body, err := json.Marshal(broker.MembershipFor(node, d, where))
+			if err != nil {
+				return err
+			}
+			if err := bus.PublishMembership(ctx, node, d.Module, body); err != nil {
+				return err
+			}
+			issued++
+		}
+	}
+	if issued > 0 {
+		fmt.Printf("  issued %d membership(s)\n", issued)
+	}
 	return nil
 }
 

internal/broker/jetstream.go

@@ -144,6 +144,7 @@ func (j *JetStream) EnsureStream(s Stream) error {
 		MaxMsgsPerSubject: int64(s.MaxMsgsPerSubject),
 		Description:       s.Why,
 	}
+	want.AllowDirect = s.Direct
 	if s.Retention == RetentionLastPerSubject {
 		// Last-per-subject is a limits stream with one message kept per subject, not a
 		// retention policy of its own — the state shape, spelled the way the server spells it.

internal/broker/membership.go

@@ -0,0 +1,131 @@
+package broker
+
+import (
+	"sort"
+	"strings"
+)
+
+// What the mesh issues an assignment to serve and to reach (novox/hq ADR 0160).
+//
+// A module's code names its tools and its events; **where they land is the mesh's to decide**, and
+// it decided it twice — once in the runtime, once here, by one rule compiled into both. Now the
+// controller composes a membership for every module on every machine and publishes it to a subject
+// only that assignment reads; the runtime serves exactly what the membership says, and the account's
+// grant is the same composition read the other way. The shape issued today is the shape the mesh
+// already had, so nothing moves when a membership first arrives; only who decides it moves.
+
+// Membership is one assignment's subjects: what this instance of a module on this machine serves,
+// and what it may reach.
+type Membership struct {
+	Node   string `json:"node"`
+	Module string `json:"module"`
+	// Serves is every address a tool of this instance answers on. `{tool}` stands for the tool's
+	// own name, which the module knows and the mesh does not need to: the mesh issues the address,
+	// the runtime fills the name. An address with a queue is shared with the module's other
+	// instances, and the bus hands each call to one of them; an address without is this instance's.
+	Serves []Served `json:"serves"`
+	// Seats is every verb of a seat this instance holds, at the subject the seat's callers use.
+	Seats []SeatServed `json:"seats,omitempty"`
+	// Emits is where an event of this module lands; `{event}` stands for the event's name.
+	Emits string `json:"emits"`
+	// Reaches is each tool this module may call, `<module>.<tool>`, to the subjects that reach it:
+	// the first is whichever instance answers, when the mesh issued one; the rest name a machine.
+	Reaches map[string][]string `json:"reaches,omitempty"`
+	// Tools is where this instance answers what it serves — the runtime's one verb of its own.
+	Tools string `json:"tools"`
+}
+
+// Served is one address a tool is answered on.
+type Served struct {
+	Subject string `json:"subject"`
+	Queue   string `json:"queue,omitempty"`
+}
+
+// SeatServed is one verb of a held seat, where its callers ask.
+type SeatServed struct {
+	Seat    string `json:"seat"`
+	Verb    string `json:"verb"`
+	Subject string `json:"subject"`
+}
+
+// MembershipSubject is the one address a runtime derives for itself: where its own membership is
+// published, from the two names its credential carries. Everything else is in the membership.
+func MembershipSubject(node, module string) string {
+	return "mesh.assignment." + node + "." + module
+}
+
+// Placements is where every module runs, for deciding which instance answers for the module.
+type Placements struct {
+	// Nodes is each module's machines.
+	Nodes map[string][]string
+	// Interchangeable is each module whose definition says its instances are the same anywhere,
+	// so the module's plain subject is issued to all of them in one queue.
+	Interchangeable map[string]bool
+}
+
+// AnswersForTheModule says whether an instance of a module on one machine is issued the module's
+// plain subject: when it is the only instance, or when the definition says instances are
+// interchangeable. A stateful module on two machines gets only its machines' subjects, so a call
+// that names none reaches nothing rather than the wrong store.
+func (p Placements) AnswersForTheModule(module string) bool {
+	return len(p.Nodes[module]) <= 1 || p.Interchangeable[module]
+}
+
+// MembershipFor composes one assignment's membership from what it declared and where everything
+// runs. The subjects are the ones PermissionsFor grants, derived here once more only until the
+// grant itself is read from the membership — which is the next step, not this one.
+func MembershipFor(node string, d Declared, where Placements) Membership {
+	own := "mesh.mod." + d.Module
+	m := Membership{
+		Node: node, Module: d.Module,
+		Emits: own + ".event.{event}",
+		Tools: own + ".tool.tools",
+	}
+	// This machine's address always; the module's when this instance answers for the module.
+	m.Serves = append(m.Serves, Served{Subject: own + ".tool.{tool}." + node})
+	if where.AnswersForTheModule(d.Module) {
+		m.Serves = append(m.Serves, Served{Subject: own + ".tool.{tool}", Queue: "serve." + d.Module})
+	}
+	for _, s := range d.Holds {
+		for _, verb := range s.Serves {
+			m.Seats = append(m.Seats, SeatServed{Seat: s.Name, Verb: verb, Subject: seatToolSubject(s, verb, node)})
+		}
+	}
+	if len(d.Invokes) > 0 {
+		m.Reaches = map[string][]string{}
+		for _, t := range d.Invokes {
+			if t == "*" || strings.HasPrefix(t, "seat:") {
+				continue // every tool, or a role's: addressed by name, not resolved per instance
+			}
+			module, tool, ok := strings.Cut(t, ".")
+			if !ok {
+				continue
+			}
+			var reach []string
+			if where.AnswersForTheModule(module) {
+				reach = append(reach, "mesh.mod."+module+".tool."+tool)
+			}
+			nodes := append([]string{}, where.Nodes[module]...)
+			sort.Strings(nodes)
+			for _, n := range nodes {
+				reach = append(reach, "mesh.mod."+module+".tool."+tool+"."+n)
+			}
+			m.Reaches[t] = reach
+		}
+	}
+	return m
+}
+
+// PlacementsOf reads where everything runs from the records the bus's accounts are composed from.
+func PlacementsOf(r Records, interchangeable map[string]bool) Placements {
+	p := Placements{Nodes: map[string][]string{}, Interchangeable: interchangeable}
+	for node, declared := range r.Assigned {
+		for _, d := range declared {
+			p.Nodes[d.Module] = append(p.Nodes[d.Module], node)
+		}
+	}
+	for _, nodes := range p.Nodes {
+		sort.Strings(nodes)
+	}
+	return p
+}

internal/broker/membership_test.go

@@ -0,0 +1,75 @@
+package broker
+
+import (
+	"reflect"
+	"testing"
+)
+
+// The mesh issues an assignment's subjects (novox/hq ADR 0160): a module alone on one machine
+// answers for the module and for its machine; a stateful module on two machines answers only for
+// each machine; one that says its instances are interchangeable answers for the module everywhere;
+// a holder serves its seat's verbs; and what a module may reach is resolved the same way.
+func TestAMembershipIsIssuedFromWhereEverythingRuns(t *testing.T) {
+	records := Records{Assigned: map[string][]Declared{
+		"anchor": {
+			{Module: "postgres", Serves: []string{"query"}, Holds: []Seat{{Name: "mesh-store", Scope: "mesh", Serves: []string{"databases", "query"}}}},
+			{Module: "catalog", Invokes: []string{"postgres.query", "search.find"}},
+		},
+		"home-server": {
+			{Module: "postgres"},
+			{Module: "search"},
+			{Module: "dashboard", Invokes: []string{"postgres.query"}},
+		},
+		"laptop": {{Module: "search"}},
+	}, Interchangeable: map[string]bool{"search": true}}
+	where := PlacementsOf(records, records.Interchangeable)
+
+	pg := MembershipFor("anchor", records.Assigned["anchor"][0], where)
+	if !reflect.DeepEqual(pg.Serves, []Served{{Subject: "mesh.mod.postgres.tool.{tool}.anchor"}}) {
+		t.Fatalf("a stateful module on two machines answers only for its machine: %+v", pg.Serves)
+	}
+	if len(pg.Seats) != 2 || pg.Seats[0].Subject != "mesh.seat.mesh-store.tool.databases" {
+		t.Fatalf("the holder serves the seat's verbs at the seat's subjects: %+v", pg.Seats)
+	}
+	if pg.Emits != "mesh.mod.postgres.event.{event}" || pg.Tools != "mesh.mod.postgres.tool.tools" {
+		t.Fatalf("events and the tools verb: %+v", pg)
+	}
+
+	search := MembershipFor("laptop", records.Assigned["laptop"][0], where)
+	if !reflect.DeepEqual(search.Serves, []Served{
+		{Subject: "mesh.mod.search.tool.{tool}.laptop"},
+		{Subject: "mesh.mod.search.tool.{tool}", Queue: "serve.search"},
+	}) {
+		t.Fatalf("an interchangeable module answers for the module in the queue too: %+v", search.Serves)
+	}
+
+	dashboard := MembershipFor("home-server", records.Assigned["home-server"][2], where)
+	if !reflect.DeepEqual(dashboard.Serves, []Served{
+		{Subject: "mesh.mod.dashboard.tool.{tool}.home-server"},
+		{Subject: "mesh.mod.dashboard.tool.{tool}", Queue: "serve.dashboard"},
+	}) {
+		t.Fatalf("a module alone on one machine answers for the module: %+v", dashboard.Serves)
+	}
+	if !reflect.DeepEqual(dashboard.Reaches["postgres.query"],
+		[]string{"mesh.mod.postgres.tool.query.anchor", "mesh.mod.postgres.tool.query.home-server"}) {
+		t.Fatalf("reaching a stateful module names each machine and no plain subject: %v", dashboard.Reaches)
+	}
+	catalog := MembershipFor("anchor", records.Assigned["anchor"][1], where)
+	if !reflect.DeepEqual(catalog.Reaches["search.find"],
+		[]string{"mesh.mod.search.tool.find", "mesh.mod.search.tool.find.home-server", "mesh.mod.search.tool.find.laptop"}) {
+		t.Fatalf("reaching an interchangeable module offers the plain subject first: %v", catalog.Reaches)
+	}
+	if MembershipSubject("anchor", "postgres") != "mesh.assignment.anchor.postgres" {
+		t.Fatal("the one subject a runtime derives for itself")
+	}
+}
+
+func TestAnAccountMayReadItsOwnMembershipAndNoOthers(t *testing.T) {
+	perms, err := PermissionsFor(Principal{Kind: KindModule, Node: "anchor", Module: "postgres", PasswordHash: "x"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	has(t, perms.Subscribe, "mesh.assignment.anchor.postgres")
+	has(t, perms.Publish, "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.anchor.postgres")
+	hasNot(t, perms.Subscribe, "mesh.assignment.>")
+}

internal/broker/nats.go

@@ -298,6 +298,10 @@ func PermissionsFor(p Principal) (Permissions, error) {
 		// away — no other principal may subscribe this namespace, and a caller's authority is
 		// still granted per tool, by name, on the publish side.
 		sub = append(sub, own+".tool.>")
+		// Its own membership (ADR 0160): the one subject a runtime derives for itself, read
+		// directly from the stream and followed live. Nothing else's.
+		sub = append(sub, MembershipSubject(p.Node, p.Module))
+		pub = append(pub, "$JS.API.DIRECT.GET."+AssignmentsStream+"."+MembershipSubject(p.Node, p.Module))
 
 		// 1b. The tools it calls, if its manifest says it calls any (novox/hq ADR 0152). The same
 		//     grant a person gets and derived the same way, so "what may this module ask" is

internal/broker/streams.go

@@ -47,8 +47,14 @@ type Stream struct {
 	// Why is carried into the assertion so an operator reading the server's own state finds the
 	// reason there, rather than only in a repository they may not have.
 	Why string
+	// Direct lets a client read a subject's last message without a consumer, which is how a
+	// runtime reads its own membership with no JetStream API beyond one request (ADR 0160).
+	Direct bool
 }
 
+// AssignmentsStream holds every assignment's membership, the newest per subject.
+const AssignmentsStream = "ASSIGNMENTS"
+
 // MeshStreams is the foundation set, in the order a person reads it.
 //
 // **CONTROL names its subjects rather than taking `mesh.control.>`**, because heartbeats live
@@ -78,6 +84,14 @@ func MeshStreams() []Stream {
 			Why: "one declaration per node, always the newest; a node that sees sequence n refuses " +
 				"n-1 by construction (issue 107)",
 		},
+		{
+			Name:      AssignmentsStream,
+			Subjects:  []string{"mesh.assignment.*.*"},
+			Retention: RetentionLastPerSubject,
+			Direct:    true,
+			Why: "one membership per assignment, always the newest: what the mesh issued this module " +
+				"on this machine to serve and to reach (ADR 0160); read directly by the runtime it is for",
+		},
 		{
 			Name: EventsStream,
 			// A seat's own events ride here too: they are 1:many like any event, and the

internal/broker/streams_test.go

@@ -123,9 +123,10 @@ func subjectMatches(filter, subject string) bool {
 // Each relationship's retention is the thing that makes it what it is (design 29 §4).
 func TestEachStreamCarriesTheRetentionItsShapeNeeds(t *testing.T) {
 	want := map[string]Retention{
-		"CONTROL": RetentionWorkQueue,
-		"NODES":   RetentionLastPerSubject,
-		"EVENTS":  RetentionLimits,
+		"CONTROL":     RetentionWorkQueue,
+		"NODES":       RetentionLastPerSubject,
+		"EVENTS":      RetentionLimits,
+		"ASSIGNMENTS": RetentionLastPerSubject,
 	}
 	got := map[string]Retention{}
 	for _, s := range MeshStreams() {

internal/broker/testdata/composed.conf

@@ -37,18 +37,18 @@ accounts {
         subscribe: { allow: ["_DELIVER.one", "_DELIVER.one.>", "_INBOX.node.one.>", "mesh.node.one.declare"] }
       } }
       { user: "one.telegram", password: "$2a$11$tttttttttttttttttttttt", permissions: {
-        publish: { allow: ["$JS.ACK.EVENTS.one_telegram.>", "$JS.ACK.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker.>", "$JS.API.CONSUMER.INFO.EVENTS.one_telegram", "$JS.API.CONSUMER.INFO.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.one_telegram", "mesh.seat.telegram-sender.event.delivered", "mesh.seat.telegram-sender.event.failed"] }
-        subscribe: { allow: ["_DELIVER.SEAT_TELEGRAM_SENDER_worker", "_DELIVER.SEAT_TELEGRAM_SENDER_worker.>", "_INBOX.one.telegram.>", "mesh.mod.telegram.tool.>", "mesh.seat.telegram-sender.accept.send"] }
+        publish: { allow: ["$JS.ACK.EVENTS.one_telegram.>", "$JS.ACK.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker.>", "$JS.API.CONSUMER.INFO.EVENTS.one_telegram", "$JS.API.CONSUMER.INFO.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.one_telegram", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.one.telegram", "mesh.seat.telegram-sender.event.delivered", "mesh.seat.telegram-sender.event.failed"] }
+        subscribe: { allow: ["_DELIVER.SEAT_TELEGRAM_SENDER_worker", "_DELIVER.SEAT_TELEGRAM_SENDER_worker.>", "_INBOX.one.telegram.>", "mesh.assignment.one.telegram", "mesh.mod.telegram.tool.>", "mesh.seat.telegram-sender.accept.send"] }
         allow_responses: { max: 1, ttl: "1m" }
       } }
       { user: "two.audit", password: "$2a$11$aaaaaaaaaaaaaaaaaaaaaa", permissions: {
-        publish: { allow: ["$JS.ACK.EVENTS.two_audit.>", "$JS.API.CONSUMER.INFO.EVENTS.two_audit", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_audit"] }
-        subscribe: { allow: ["_INBOX.two.audit.>", "mesh.mod.audit.tool.>", "mesh.mod.shop.event.order.placed"] }
+        publish: { allow: ["$JS.ACK.EVENTS.two_audit.>", "$JS.API.CONSUMER.INFO.EVENTS.two_audit", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_audit", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.two.audit"] }
+        subscribe: { allow: ["_INBOX.two.audit.>", "mesh.assignment.two.audit", "mesh.mod.audit.tool.>", "mesh.mod.shop.event.order.placed"] }
         allow_responses: { max: 1, ttl: "1m" }
       } }
       { user: "two.shop", password: "$2a$11$ssssssssssssssssssssss", permissions: {
-        publish: { allow: ["$JS.ACK.EVENTS.two_shop.>", "$JS.API.CONSUMER.INFO.EVENTS.two_shop", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_shop", "mesh.mod.shop.event.order.placed", "mesh.seat.telegram-sender.accept.send"] }
-        subscribe: { allow: ["_INBOX.two.shop.>", "mesh.mod.shop.tool.>"] }
+        publish: { allow: ["$JS.ACK.EVENTS.two_shop.>", "$JS.API.CONSUMER.INFO.EVENTS.two_shop", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_shop", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.two.shop", "mesh.mod.shop.event.order.placed", "mesh.seat.telegram-sender.accept.send"] }
+        subscribe: { allow: ["_INBOX.two.shop.>", "mesh.assignment.two.shop", "mesh.mod.shop.tool.>"] }
         allow_responses: { max: 1, ttl: "1m" }
       } }
     ]

internal/broker/users.go

@@ -47,6 +47,9 @@ type Records struct {
 	Enrolling []string
 	// People is each person's name against the tools they may invoke, `*` for an administrator.
 	People map[string][]string
+	// Interchangeable is each module whose definition says its instances are the same anywhere
+	// (ADR 0160), which decides whether the module's plain subject is issued to every instance.
+	Interchangeable map[string]bool
 }
 
 // Users is every user the composed file should contain, in the order it will be written.

internal/catalogue/manifest.go

@@ -293,6 +293,12 @@ type Manifest struct {
 	// module claiming a seat answers what that seat's protocol promises (novox/hq ADR 0118).
 	Tools []string `json:"tools,omitempty"`
 
+	// Instances says whether this module's instances are the same anywhere — `interchangeable` —
+	// so a call that names no machine may be answered by any of them (novox/hq ADR 0160). A fact
+	// about the software, not about the bus: a stateless web tool says it; a database does not,
+	// and its instances are then each addressed by machine, never confused for one another.
+	Instances string `json:"instances,omitempty"`
+
 	// Invokes are the tools this module calls, each `<module>.<tool>` or a role's `seat:<seat>.<verb>`,
 	// or the single entry `*` for every tool on the mesh (novox/hq ADR 0152, ADR 0154).
 	//
@@ -1173,6 +1179,11 @@ func ParseManifest(raw []byte) (Manifest, error) {
 				m.Module, r))
 		}
 	}
+	if m.Instances != "" && m.Instances != InstancesInterchangeable {
+		problems = append(problems, fmt.Sprintf(
+			"%s says its instances are %q; the one word is %q, for a module that is the same on every machine",
+			m.Module, m.Instances, InstancesInterchangeable))
+	}
 	for _, offer := range m.Provides {
 		p := offer.Name
 		if !name.MatchString(p) {
@@ -1960,3 +1971,7 @@ func (o OwnSecrets) Paths() map[string]string {
 	}
 	return out
 }
+
+// InstancesInterchangeable is the one value of a definition's `instances`: the module is the same
+// on every machine, so any instance may answer for the module.
+const InstancesInterchangeable = "interchangeable"

internal/inventory/busrecords.go

@@ -49,7 +49,8 @@ func (i *Inventory) BusRecords(ctx context.Context) (broker.Records, error) {
 		}
 	}
 
-	out := broker.Records{Assigned: map[string][]broker.Declared{}, People: map[string][]string{}}
+	out := broker.Records{Assigned: map[string][]broker.Declared{}, People: map[string][]string{},
+		Interchangeable: map[string]bool{}}
 	for _, n := range nodes {
 		out.Nodes = append(out.Nodes, n.Name)
 		modules, err := i.Assigned(ctx, n.Name)
@@ -72,6 +73,9 @@ func (i *Inventory) BusRecords(ctx context.Context) (broker.Records, error) {
 						"be derived", module, n.Name)
 			}
 			out.Assigned[n.Name] = append(out.Assigned[n.Name], declaredFor(m, seats))
+			if m.Instances == catalogue.InstancesInterchangeable {
+				out.Interchangeable[m.Module] = true
+			}
 		}
 	}
 

internal/link/bus.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"github.com/novox/mesh-controller/internal/broker"
 	"time"
 
 	"github.com/nats-io/nats.go"
@@ -145,6 +146,16 @@ func (b OverNATS) PublishSeatEvent(ctx context.Context, seat, event string, body
 	return nil
 }
 
+// PublishMembership issues one assignment what it serves and reaches (novox/hq ADR 0160), last per
+// subject, so the runtime that connects later reads the current one and one that is running follows.
+func (b OverNATS) PublishMembership(ctx context.Context, node, module string, body []byte) error {
+	_, err := b.JS.Publish(broker.MembershipSubject(node, module), body, nats.Context(ctx))
+	if err != nil {
+		return fmt.Errorf("issuing %s on %s its membership: %w", module, node, err)
+	}
+	return nil
+}
+
 func (b OverNATS) PublishDeclaration(ctx context.Context, node string, body []byte) error {
 	_, err := b.JS.Publish(DeclareSubject(node), body, nats.Context(ctx))
 	if err != nil {