The mesh's one resolver: its seat, a provider's address, zones, and a node's hosts file (hq ADR 0194, 0196, 0199)

- mesh-dns-resolver: a mesh seat delivering wildcard-resolution, so every node's resolver
  configuration resolves to its one holder; node-dns-resolver kept until nothing claims it.
- ${bound:<provision>:address}: the providing machine's private address, for the one consumer
  that cannot use a name — a machine's resolver configuration.
- zone: a module declares the zone it answers and the listen that answers it; the controller
  settles it per node, refuses duplicates and shadowing, and hands the resolver .Zones to forward.
- node-hosts-file: a node seat whose holder owns /etc/hosts, with entries/add/remove.
The resolver tests follow the catalogue: no runtime dns (containers copy the machine's resolvers),
live-restore held by resolv-conf, resolv.conf naming the resolver by address then a public one.

cmd/mesh-controller/network_test.go

@@ -254,11 +254,10 @@ func theResolver(t *testing.T) catalogue.Manifest {
 	return m
 }
 
-// The resolver is handed every machine on the private network as a wildcard, the same set and the
+// The resolver is handed every machine on the private network as a wildcard, and is handed it again
-// same source as the hosts file, and is handed it again when a machine leaves — through the
+// when a machine leaves — through the module's own manifest asking for the fact, with no module of the
-// module's own manifest asking for the fact, with no module of the mesh's own in between (hal
+// mesh's own in between (hal dnsmasq-app conversion, novox/hq 08-connectivity). It is the mesh's one
-// dnsmasq-app conversion, novox/hq 08-connectivity). The runtime on that machine is pointed at the
+// resolver (ADR 0194), and the container runtime is given no resolver of its own (ADR 0196).
-// machine's own address, where the resolver answers for its containers.
 func TestTheResolverIsToldEveryMachineOnTheNetworkAndToldAgainWhenOneLeaves(t *testing.T) {
 	open := aMesh(t)
 	ctx := t.Context()
@@ -293,11 +292,12 @@ func TestTheResolverIsToldEveryMachineOnTheNetworkAndToldAgainWhenOneLeaves(t *t
 			t.Errorf("the resolver's machines lack %q:\n%s", want, first)
 		}
 	}
+	// The container runtime is given no resolver of its own (novox/hq ADR 0196): it copies its
+	// machine's, which name the mesh's resolver first. A `dns` key would be a second account of where a
+	// container asks, read only when the runtime starts.
 	for _, r := range composed(t, open, "anchor").Resources {
 		if r["id"] == "dnsmasq.runtime-dns" {
-			if !strings.Contains(r["content"].(string), `"10.77.0.1"`) || r["into"] != "json" {
+			t.Errorf("the resolver still writes the runtime's own dns: %v", r)
-				t.Errorf("the runtime is not pointed at this machine's own address, written into its file: %v", r)
-			}
 		}
 	}
 

cmd/mesh-controller/plan.go

@@ -657,6 +657,13 @@ func renderingFor(ctx context.Context, open *stores, node string,
 		machines[name] = at
 	}
 
+	// And every zone a module in the mesh answers itself (novox/hq ADR 0199), for the mesh's resolver
+	// to forward.
+	zones, err := zonesInTheMesh(ctx, open)
+	if err != nil {
+		return catalogue.Rendering{}, inventory.Node{}, err
+	}
+
 	// **The bus is never public** (novox/hq ADR 0169). It was a foundation port — widened from the
 	// broker's own `from: mesh` to from-anywhere on the broker's host, so a machine could enrol
 	// before it had an address on the private network. A machine joins through the tunnel now, and
@@ -726,14 +733,79 @@ func renderingFor(ctx context.Context, open *stores, node string,
 		BusMembership: memberships[node],
 		Settings:      settings, Generators: gens, Grants: grants, Needed: needed, Ports: ports,
 		Certificate: certificate, Authority: authority, Mesh: private, Names: names,
-		Machines: machines,
+		Machines: machines, Zones: zones,
-		Suffix:   overlay.Suffix(), MeshRange: meshRange, TunnelInterface: overlay.Interface, Accounts: accounts, Foundation: foundation,
+		Suffix: overlay.Suffix(), MeshRange: meshRange, TunnelInterface: overlay.Interface, Accounts: accounts, Foundation: foundation,
 		Kept: kept, Adopted: record.Adopted, OutwardLinks: outwardLinks,
 		Given: given, Taken: taken, Seats: seats, ArtifactStore: artifactStore, Built: built,
 		BusUsers: busUsers,
 	}, record, nil
 }
 
+// zonesInTheMesh is every zone a module in the mesh declares, where the mesh placed it (novox/hq ADR
+// 0199): the zone settled from that node's settings, the node's private address, the port the
+// answering listen is published on there.
+//
+// Read across every machine's resolution, as the roster once read routed names: a node whose set does
+// not compose declares nothing and is passed over, so one broken machine does not cost the rest their
+// zones; a store that cannot be read is raised, naming the machine, because returning the zones
+// without it would withdraw them from the resolver as if the operator had (novox/hq 04-ISSUES/152).
+// What the mesh refuses about the zones together — one declared twice, one shadowing the mesh's
+// suffix or a node's public domain — is refused here, by name.
+func zonesInTheMesh(ctx context.Context, open *stores) ([]catalogue.ZoneAt, error) {
+	inv := open.inventory
+	places, err := inv.Overlays(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("where the machines are cannot be read: %w", err)
+	}
+	address := map[string]string{}
+	for _, p := range places {
+		if strings.TrimSpace(p.Address) != "" {
+			address[p.Name] = p.Address
+		}
+	}
+	nodes, err := inv.Nodes(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("which machines the mesh has cannot be read: %w", err)
+	}
+	var zones []catalogue.ZoneAt
+	var public []string
+	for _, n := range nodes {
+		plan, _, err := planFor(ctx, open, n.Name)
+		switch {
+		case unresolvable(err):
+			continue
+		case err != nil:
+			return nil, fmt.Errorf("the zones %s answers cannot be read: %w", n.Name, err)
+		}
+		if plan.PublicDomain != "" {
+			public = append(public, plan.PublicDomain)
+		}
+		for _, m := range plan.Modules {
+			if m.Zone == nil {
+				continue
+			}
+			at := address[n.Name]
+			if at == "" {
+				// Not on the private network yet: nothing could reach its answerer.
+				continue
+			}
+			published, layers, err := portsGivenOn(ctx, inv, n.Name, m)
+			if err != nil {
+				return nil, fmt.Errorf("the zone %s declares on %s cannot be read: %w", m.Module, n.Name, err)
+			}
+			z, err := catalogue.ZoneOn(m, layers, published, n.Name, at)
+			if err != nil {
+				return nil, err
+			}
+			zones = append(zones, *z)
+		}
+	}
+	if problems := catalogue.ZonesProblems(zones, overlay.Suffix(), public); len(problems) > 0 {
+		return nil, fmt.Errorf("the mesh's zones cannot be forwarded:\n  - %s", strings.Join(problems, "\n  - "))
+	}
+	return zones, nil
+}
+
 // certificateFor is what the mesh certifies about one machine's internal name.
 //
 // It reaches across two contexts and reads neither one's store from the other: `inventory` knows

internal/catalogue/bound_into_files.go

@@ -21,8 +21,9 @@ import (
 // formats and gains no fields.
 //
 // **It stays name-agnostic** ([ADR 0027]). The mesh does not learn what a `postgres-database` is:
-// `at`, `as` and `from` are facts about any provision at all, and everything else comes from what
+// `at`, `as`, `from` and `address` (the providing machine's private address, novox/hq ADR 0194) are
-// the provider said it serves — whose keys are agreed by the requirement's name, not by this file.
+// facts about any provision at all, and everything else comes from what the provider said it
+// serves — whose keys are agreed by the requirement's name, not by this file.
 
 // bound is where a module says a value from one of its bindings belongs:
 // ${bound:<provision>.<key>}.

internal/catalogue/bound_into_files_test.go

@@ -232,3 +232,34 @@ func TestTwoModulesOnOneNodeAreTwoIdentities(t *testing.T) {
 		t.Fatal("one module on two machines shares an identity")
 	}
 }
+
+// A machine's resolver configuration must name its resolver by address — it cannot resolve the name
+// of the thing it resolves names with (novox/hq ADR 0194). So a binding offers the providing
+// machine's private address beside its name, and only when the machine has one.
+func TestABindingOffersTheProvidersAddress(t *testing.T) {
+	consumer := func() Resolution {
+		return Resolution{
+			Node: "workstation",
+			Modules: []Manifest{{
+				Module:   "resolv-conf",
+				Requires: []string{"wildcard-resolution"},
+				Resources: []map[string]any{{
+					"id": "resolv", "type": "file", "path": "/etc/resolv.conf", "mode": "0644",
+					"content": "nameserver ${bound:wildcard-resolution:address}\n",
+				}},
+			}},
+			Needs: []Needed{{Name: "wildcard-resolution", From: "anchor", At: "anchor.internal", For: "resolv-conf"}},
+		}
+	}
+	out, err := consumer().Declaration(Rendering{Machines: map[string]string{"anchor.internal": "10.77.0.1"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fileNamed(out, "resolv-conf.resolv")["content"]; got != "nameserver 10.77.0.1\n" {
+		t.Fatalf("the resolver is not named by its address: %q", got)
+	}
+	// A machine with no address yet: refused, never written with a blank where the address belongs.
+	if _, err := consumer().Declaration(Rendering{}); err == nil {
+		t.Fatal("a file naming an address the mesh does not have was composed")
+	}
+}

internal/catalogue/declaration.go

@@ -155,6 +155,10 @@ type Rendering struct {
 	// standing beside the machines and looking as real as they do.
 	Machines map[string]string
 
+	// Zones is every zone a module in the mesh answers itself, where it is answered (novox/hq ADR
+	// 0199): the mesh's resolver forwards each one there.
+	Zones []ZoneAt
+
 	Settings   SettingsBy
 	Generators map[string]Generator
 	// Grants are the credentials this node must create, for the provisions it offers. Passed in
@@ -732,6 +736,16 @@ func (r Resolution) compose(with Rendering, owner map[string]string,
 				known[provision] = values
 			}
 		}
+		// And the providing machine's private address, beside its name (novox/hq ADR 0194). A name is
+		// what nearly every consumer wants; the one that cannot use it is a machine's resolver
+		// configuration, which must reach the resolver before it can resolve anything — the resolver's
+		// own name included. Absent when the machine has no address yet, so a file naming it is refused
+		// rather than written with a blank where an address belongs.
+		for _, values := range known {
+			if address := with.Machines[values["at"]]; address != "" {
+				values["address"] = address
+			}
+		}
 		// And what the module is called through each requirement it contributes to (novox/hq
 		// 04-ISSUES/122) — the same composition its binding file carries.
 		for provision, values := range known {
@@ -901,7 +915,7 @@ func (r Resolution) compose(with Rendering, owner map[string]string,
 		// plane's; making a name resolve is the module's software. Emitted as ordinary files under
 		// this module's name, so they are applied, reported and removed exactly as anything else
 		// it declares.
-		given, err := FactsInto(m, r, with.Names, with.Machines, with.Accounts, with.Suffix)
+		given, err := FactsWithZonesInto(m, r, with.Names, with.Machines, with.Accounts, with.Suffix, with.Zones)
 		if err != nil {
 			return nil, err
 		}

internal/catalogue/manifest.go

@@ -540,6 +540,10 @@ type Manifest struct {
 	// `restart-on` names to restart when the roster changes.
 	Facts map[string]RosterFile `json:"facts,omitempty"`
 
+	// Zone is the zone of names this module answers itself, and the listen that answers it (novox/hq
+	// ADR 0199). The mesh's resolver forwards the zone to it; nothing here names an address.
+	Zone *Zone `json:"zone,omitempty"`
+
 	// Certificate is where this module wants a certificate for its machine's name inside the
 	// mesh, and where the key that goes with it can be found.
 	//
@@ -1742,6 +1746,7 @@ func ParseManifest(raw []byte) (Manifest, error) {
 		}
 	}
 
+	problems = append(problems, zoneProblems(m)...)
 	if len(problems) > 0 {
 		sort.Strings(problems)
 		return Manifest{}, fmt.Errorf("this manifest cannot be used:\n  - %s",

internal/catalogue/resolver_manifests_test.go

@@ -48,9 +48,12 @@ func TestTheResolverForwardsToFixedUpstreamsAndNeverReadsResolvConf(t *testing.T
 	}
 	for _, want := range []string{
 		"\nno-resolv\n", "\nserver=1.1.1.1\n", "\nserver=8.8.8.8\n",
-		// Loopback is the mesh-wide setting's default; a machine answering its own LAN adds its
+		// The private address and loopback, never a LAN's (novox/hq ADR 0194): a device that is not a
-		// address there (novox/hq issue 198).
+		// member cannot reach what the mesh's names point at.
-		"\nlisten-address=${setting:listen-addresses}\n", "\nlisten-address=${machine:address}\n", "\nbind-dynamic\n",
+		"\nlisten-address=127.0.0.1\n", "\nlisten-address=${machine:address}\n", "\nbind-dynamic\n",
+		// No hosts file and no operator's files: the mesh's resolver answers every node (ADR 0199).
+		"\nno-hosts\n",
+		"\nconf-file=" + m.Facts["zones"].Path + "\n",
 		"\ndomain-needed\n", "\nbogus-priv\n",
 		"\nconf-file=" + m.Facts["node-zones"].Path + "\n",
 	} {
@@ -73,7 +76,15 @@ func TestTheResolverForwardsToFixedUpstreamsAndNeverReadsResolvConf(t *testing.T
 			t.Errorf("the resolver listens on %s", taken)
 		}
 	}
-	// And the file that decides what the machine asks names it there, alone.
+	// Never a directory or a file the operator keeps: a line written for one machine's programs would
+	// become an answer for every node (ADR 0199).
+	for _, never := range []string{"conf-dir=", "addn-hosts=", "listen-address=${setting:"} {
+		if strings.Contains(config, never) {
+			t.Errorf("the mesh's resolver still reads or listens on %q", never)
+		}
+	}
+	// And the file that decides what the machine asks names the mesh's resolver first, by address,
+	// and a public one second, asked only when the first is silent (ADR 0196).
 	var resolv string
 	for _, r := range catalogueManifest(t, "resolv-conf").Resources {
 		if r["path"] == "/etc/resolv.conf" {
@@ -86,13 +97,16 @@ func TestTheResolverForwardsToFixedUpstreamsAndNeverReadsResolvConf(t *testing.T
 			nameservers = append(nameservers, strings.TrimPrefix(line, "nameserver "))
 		}
 	}
-	if len(nameservers) != 1 || nameservers[0] != "127.0.0.1" {
+	if len(nameservers) != 2 || nameservers[0] != "${bound:wildcard-resolution:address}" || nameservers[1] != "1.1.1.1" {
-		t.Errorf("resolv.conf names %v; the predecessor's names the mesh's resolver alone at 127.0.0.1", nameservers)
+		t.Errorf("resolv.conf names %v; the mesh's resolver by address first, a public one second", nameservers)
 	}
-	// The split-DNS alternative points at the same address, or a machine that keeps
+	if !strings.Contains(resolv, "\noptions timeout:1 attempts:1") {
+		t.Errorf("the fallback is not reached after one short attempt:\n%s", resolv)
+	}
+	// The split-DNS alternative points at the same resolver, or a machine that keeps
 	// systemd-resolved in charge would route the mesh's suffix to nothing.
 	for _, r := range catalogueManifest(t, "resolved-split-dns").Resources {
-		if content, _ := r["content"].(string); content != "" && !strings.Contains(content, "DNS=127.0.0.1\n") {
+		if content, _ := r["content"].(string); content != "" && !strings.Contains(content, "DNS=${bound:wildcard-resolution:address}\n") {
 			t.Errorf("resolved-split-dns does not point at the resolver's address:\n%s", content)
 		}
 	}
@@ -100,7 +114,8 @@ func TestTheResolverForwardsToFixedUpstreamsAndNeverReadsResolvConf(t *testing.T
 
 // The resolver and what points the machine at it compose on one machine, and what arrives is the
 // mesh's account of every machine as a wildcard, the suffix kept local, the daemon restarting on
-// that file, and the runtime pointed at this machine's own address.
+// that file, the machine pointed at the resolver by address, and the runtime given no resolver of
+// its own but kept running across a restart (ADR 0196).
 func TestTheResolverAndWhatAsksItComposeOnOneMachine(t *testing.T) {
 	got, err := Resolve(resolverShelf(t), []string{"dnsmasq", "resolv-conf"},
 		Node{Name: "anchor", At: "anchor.internal"}, World{})
@@ -115,6 +130,7 @@ func TestTheResolverAndWhatAsksItComposeOnOneMachine(t *testing.T) {
 		// issue 111) — the resolver's zones read only the second, and in this scenario the two
 		// happen to be the same map, since nothing routed is part of it.
 		Names: twoMachines, Machines: twoMachines, Suffix: "internal",
+		Zones:    []ZoneAt{{Zone: "incus", Address: "10.42.0.2", Port: 5353}},
 		Needed:   map[string]map[string]string{"dnsmasq": {"broker": "sealed"}},
 		Settings: SettingsBy{"dnsmasq": {{From: "the mesh", Values: map[string]any{"listen-addresses": "127.0.0.1"}}}},
 	})
@@ -144,24 +160,29 @@ func TestTheResolverAndWhatAsksItComposeOnOneMachine(t *testing.T) {
 	for _, id := range service["restart-on"].([]any) {
 		reflects[id.(string)] = true
 	}
-	if !reflects["dnsmasq.config"] || !reflects["dnsmasq.fact-node-zones"] {
+	if !reflects["dnsmasq.config"] || !reflects["dnsmasq.fact-node-zones"] || !reflects["dnsmasq.fact-zones"] {
-		t.Errorf("the daemon does not restart on its configuration and the machines file both: %v", service["restart-on"])
+		t.Errorf("the daemon does not restart on its configuration, the machines and the zones: %v", service["restart-on"])
+	}
+	if z, _ := ids["dnsmasq.fact-zones"]["content"].(string); !strings.Contains(z, "server=/incus/10.42.0.2#5353\n") {
+		t.Errorf("the resolver was not told to forward the zone to its answerer:\n%s", z)
 	}
 
-	// The runtime's own file, written into (novox/hq ADR 0102) with the keys this module states:
+	// The runtime's own file, written into (novox/hq ADR 0102) with one key, by what decides how the
-	// where containers resolve, and that a restart keeps them running — because the runtime reads
+	// machine resolves: a restart keeps every container running. No `dns` — a container copies its
-	// `dns` only when it starts, and the one restart that needs is the operator's (issue 110).
+	// machine's resolvers (ADR 0196), and the mesh's resolver is not written into the runtime twice.
-	runtime := ids["dnsmasq.runtime-dns"]
+	if ids["dnsmasq.runtime-dns"] != nil {
+		t.Errorf("the resolver still writes the runtime's dns: %v", ids["dnsmasq.runtime-dns"])
+	}
+	runtime := ids["resolv-conf.runtime-config"]
 	if runtime == nil || runtime["path"] != "/etc/docker/daemon.json" || runtime["into"] != "json" {
-		t.Fatalf("the runtime's dns is not written into its file: %v", runtime)
+		t.Fatalf("live-restore is not written into the runtime's file: %v", runtime)
 	}
 	var keys map[string]any
 	if err := json.Unmarshal([]byte(runtime["content"].(string)), &keys); err != nil {
 		t.Fatalf("the runtime's keys are not JSON: %v", err)
 	}
-	dns, _ := keys["dns"].([]any)
+	if len(keys) != 1 || keys["live-restore"] != true {
-	if len(keys) != 2 || len(dns) != 1 || dns[0] != "10.42.0.1" || keys["live-restore"] != true {
+		t.Errorf("the runtime is given %v; live-restore and nothing else", keys)
-		t.Errorf("the runtime is given %v; containers resolve at this machine's own private-network address, a restart keeps them, and nothing else is written", keys)
 	}
 	// The runtime is reloaded when that file changes, and never restarted: a restart stops every
 	// container on the machine (ADR 0102), and a reload is what turns live-restore on.
@@ -171,10 +192,10 @@ func TestTheResolverAndWhatAsksItComposeOnOneMachine(t *testing.T) {
 			continue
 		}
 		if _, restarts := r["restart-on"]; restarts {
-			t.Errorf("the resolver orders the runtime restarted, which stops every container (ADR 0102): %v", r)
+			t.Errorf("the runtime is ordered restarted, which stops every container (ADR 0102): %v", r)
 		}
 		for _, on := range asStrings(r["reload-on"]) {
-			if on == "dnsmasq.runtime-dns" {
+			if on == "resolv-conf.runtime-config" {
 				reloaded = true
 			}
 		}
@@ -184,8 +205,8 @@ func TestTheResolverAndWhatAsksItComposeOnOneMachine(t *testing.T) {
 	}
 
 	resolv := ids["resolv-conf.resolv"]
-	if resolv == nil || !strings.Contains(resolv["content"].(string), "\nnameserver 127.0.0.1\n") {
+	if resolv == nil || !strings.Contains(resolv["content"].(string), "\nnameserver 10.42.0.1\nnameserver 1.1.1.1\n") {
-		t.Fatalf("the machine is not pointed at the resolver: %v", resolv)
+		t.Fatalf("the machine is not pointed at the resolver by address, with the public fallback: %v", resolv)
 	}
 }
 

internal/catalogue/roster.go

@@ -61,6 +61,16 @@ type rosterView struct {
 	Suffix   string
 	Names    []rosterEntry
 	Machines []rosterEntry
+	// Zones is every zone a module in the mesh answers itself, with where its answerer is (novox/hq
+	// ADR 0199) — what the mesh's resolver forwards. Ordered by zone.
+	Zones []rosterZone
+}
+
+// rosterZone is one zone as a template sees it: the zone, and the address and port answering it.
+type rosterZone struct {
+	Zone    string
+	Address string
+	Port    int
 }
 
 // rosterEntry is one machine as a template sees it: its bare name, its full mesh name, its address,
@@ -80,6 +90,12 @@ type rosterEntry struct {
 // `machines` is only the machines — the two must not be confused (novox/hq 04-ISSUES/111), so both
 // are given and the template chooses.
 func FactsInto(m Manifest, r Resolution, every, machines, accounts map[string]string, suffix string) ([]map[string]any, error) {
+	return FactsWithZonesInto(m, r, every, machines, accounts, suffix, nil)
+}
+
+// FactsWithZonesInto is FactsInto with the mesh's zones in the view, for a template that ranges them.
+func FactsWithZonesInto(m Manifest, r Resolution, every, machines, accounts map[string]string, suffix string,
+	zones []ZoneAt) ([]map[string]any, error) {
 	if len(m.Facts) == 0 {
 		return nil, nil
 	}
@@ -94,6 +110,7 @@ func FactsInto(m Manifest, r Resolution, every, machines, accounts map[string]st
 		Suffix:   strings.TrimPrefix(suffixOr(suffix), "."),
 		Names:    entriesFrom(every, accounts, suffix),
 		Machines: entriesFrom(machines, accounts, suffix),
+		Zones:    zonesFrom(zones),
 	}
 
 	out := make([]map[string]any, 0, len(names))
@@ -223,3 +240,13 @@ func sortedNames(addresses map[string]string) []string {
 	sort.Strings(out)
 	return out
 }
+
+// zonesFrom is the zones a template ranges, ordered by zone so two renderings of one mesh are one file.
+func zonesFrom(zones []ZoneAt) []rosterZone {
+	out := make([]rosterZone, 0, len(zones))
+	for _, z := range zones {
+		out = append(out, rosterZone{Zone: z.Zone, Address: z.Address, Port: z.Port})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Zone < out[j].Zone })
+	return out
+}

internal/catalogue/seats.go

@@ -107,7 +107,31 @@ var defaultSeats = []Seat{
 	// that machine unresolvable in the meantime. Deleted once no registered manifest claims it.
 	{Name: "mesh-build-machine", Scope: ScopeMesh,
 		Accepts: []string{"build"}, Emits: []string{"started", "built", "log.*"}, Decision: "novox/hq ADR 0190"},
+	// **The mesh's one resolver** (novox/hq ADR 0194, 0196): every node's internal domain, held in one
+	// place, and every node and container asks it first. Delivers what a machine's resolver
+	// configuration requires, so that requirement resolves to the holder wherever it is placed.
+	{Name: "mesh-dns-resolver", Scope: ScopeMesh, Delivers: "wildcard-resolution", Decision: "novox/hq ADR 0194"},
+	// **Retired by ADR 0194, kept while a manifest still claims it** — the same reason as
+	// mesh-build-machine above: a machine still holds it until the mesh's resolver replaces it, and
+	// removing the row first would make that machine unresolvable. Deleted once nothing claims it.
 	{Name: "node-dns-resolver", Scope: ScopeNode, Decision: "novox/hq ADR 0121"},
+	// **A machine's /etc/hosts is one module's** (novox/hq ADR 0199): its holder writes the machine's
+	// own lines and keeps every other line as the operator's, changed through these three verbs on that
+	// machine alone. The controller holds none of it.
+	{Name: "node-hosts-file", Scope: ScopeNode, Decision: "novox/hq ADR 0199",
+		Serves: []Verb{
+			{Name: "entries", Description: "Every line of this machine's /etc/hosts, each marked whose it is: " +
+				"the operator's, or the block of the module or tool that writes it.",
+				Input: schema(map[string]string{}, nil)},
+			{Name: "add", Description: "Add one address and its names to the operator's lines of this machine's " +
+				"/etc/hosts — a name for this machine's own programs, not the mesh's.",
+				Input: schema(map[string]string{"address": "the IPv4 or IPv6 address",
+					"names": "the names for it, separated by spaces"}, []string{"address", "names"})},
+			{Name: "remove", Description: "Remove one name, or every line of one address, from the operator's " +
+				"lines of this machine's /etc/hosts. A line a module writes is refused, naming the module.",
+				Input: schema(map[string]string{"name": "a host name, or an address to remove every line of"},
+					[]string{"name"})},
+		}},
 	// The intrusion prevention's verbs (novox/hq ADR 0179): what a person asks a machine's ban list
 	// whatever keeps it — who is banned and why, ban one address, let one go. Every holder serves all
 	// four; the jails themselves are composed from the modules the machine runs (to-be 31).

internal/catalogue/seats_test.go

@@ -44,10 +44,10 @@ func TestTheSeatsAreAClosedSetAndEachNamesItsDecision(t *testing.T) {
 			delivered[s.Delivers] = s.Name
 		}
 	}
-	// Seventeen since node-build-agent (novox/hq ADR 0190) — sixteen once the retired
+	// Nineteen since mesh-dns-resolver (novox/hq ADR 0194) and node-hosts-file (ADR 0199) — two fewer
-	// mesh-build-machine row goes, when no registered manifest claims it any more.
+	// once the retired mesh-build-machine and node-dns-resolver rows go, when no manifest claims either.
-	if len(Seats()) != 17 {
+	if len(Seats()) != 19 {
-		t.Errorf("the mesh defines %d seats rather than 17; the set is closed, so a change here is "+
+		t.Errorf("the mesh defines %d seats rather than 19; the set is closed, so a change here is "+
 			"a decision (novox/hq ADR 0110): %s", len(Seats()), seatNames())
 	}
 }

internal/catalogue/zones.go

@@ -0,0 +1,117 @@
+package catalogue
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Zones: names a module answers itself (novox/hq ADR 0199).
+//
+// The mesh's resolver holds each node's internal domain and nothing else (ADR 0191, 0194). A module
+// whose names are its own — the lab's scenario machines, known only while a scenario runs — declares
+// the zone it answers and the listen that answers it; the controller hands the resolver's holder every
+// zone with the declaring node's private address and the port that listen is published on, and the
+// holder forwards the zone there. **A definition names no address** (ADR 0112): the zone is a setting,
+// the listen is the module's own, and where they are is the mesh's fact.
+
+// Zone is the manifest's declaration that a module answers the names in one zone.
+type Zone struct {
+	// Name is the zone: a label or a dotted name, normally `${setting:<key>}`, so the operator chooses
+	// it and the definition does not.
+	Name string `json:"name"`
+	// Listen names one of the module's listens: the DNS answerer for the zone.
+	Listen string `json:"listen"`
+}
+
+// ZoneAt is a declared zone where the mesh placed it: what the resolver's holder forwards, and where.
+type ZoneAt struct {
+	Zone    string
+	Node    string
+	Module  string
+	Address string
+	Port    int
+}
+
+// zoneProblems is what is wrong with a module's zone declaration on its own, before any node.
+func zoneProblems(m Manifest) []string {
+	if m.Zone == nil {
+		return nil
+	}
+	var problems []string
+	if strings.TrimSpace(m.Zone.Name) == "" {
+		problems = append(problems, fmt.Sprintf("%s declares a zone with no name", m.Module))
+	}
+	if !m.hasListen(m.Zone.Listen) {
+		problems = append(problems, fmt.Sprintf(
+			"%s declares zone %q answered by listen %q, and has no listen of that name",
+			m.Module, m.Zone.Name, m.Zone.Listen))
+	}
+	return problems
+}
+
+func (m Manifest) hasListen(name string) bool {
+	if name == "" {
+		return false
+	}
+	for _, l := range m.Listens {
+		if l.Name == name {
+			return true
+		}
+	}
+	return false
+}
+
+// ZoneOn is one module's zone as one node places it: the name settled from the node's settings, the
+// port its answering listen is published on there. Nothing when the module declares no zone.
+func ZoneOn(m Manifest, layers []Layer, published map[int]int, node, address string) (*ZoneAt, error) {
+	if m.Zone == nil {
+		return nil, nil
+	}
+	settled, err := Settle(map[string]any{"zone": m.Zone.Name}, layers)
+	if err != nil {
+		return nil, fmt.Errorf("%s's zone on %s: %w", m.Module, node, err)
+	}
+	zone := strings.Trim(strings.ToLower(fmt.Sprint(settled["zone"])), ".")
+	var port int
+	for _, l := range m.Listens {
+		if l.Name == m.Zone.Listen {
+			port = l.Port
+			if at, given := published[l.Port]; given {
+				port = at
+			}
+		}
+	}
+	return &ZoneAt{Zone: zone, Node: node, Module: m.Module, Address: address, Port: port}, nil
+}
+
+// ZonesProblems is what the mesh refuses about its zones together: one zone declared twice, a zone
+// that is the mesh's suffix or under it, a zone that is a node's public domain or under one. A module
+// may not shadow names the mesh's resolver or the public DNS answers.
+func ZonesProblems(zones []ZoneAt, suffix string, publicDomains []string) []string {
+	var problems []string
+	under := func(zone, domain string) bool {
+		domain = strings.Trim(strings.ToLower(domain), ".")
+		return domain != "" && (zone == domain || strings.HasSuffix(zone, "."+domain))
+	}
+	seen := map[string]ZoneAt{}
+	for _, z := range zones {
+		if other, twice := seen[z.Zone]; twice && (other.Node != z.Node || other.Module != z.Module) {
+			problems = append(problems, fmt.Sprintf("zone %q is declared by %s on %s and by %s on %s; one module answers a zone",
+				z.Zone, other.Module, other.Node, z.Module, z.Node))
+		}
+		seen[z.Zone] = z
+		if under(z.Zone, suffix) {
+			problems = append(problems, fmt.Sprintf("%s on %s declares zone %q, which is the mesh's own suffix or under it",
+				z.Module, z.Node, z.Zone))
+		}
+		for _, d := range publicDomains {
+			if under(z.Zone, d) {
+				problems = append(problems, fmt.Sprintf("%s on %s declares zone %q, which is the public domain %q or under it",
+					z.Module, z.Node, z.Zone, d))
+			}
+		}
+	}
+	sort.Strings(problems)
+	return problems
+}

internal/catalogue/zones_test.go

@@ -0,0 +1,78 @@
+package catalogue
+
+import (
+	"strings"
+	"testing"
+)
+
+// A zone names the listen that answers it, or there is nothing to forward to (novox/hq ADR 0199).
+func TestAZoneMustNameOneOfTheModulesListens(t *testing.T) {
+	_, err := ParseManifest([]byte(`{"module":"lab","version":"1",
+		"listens":[{"name":"dns","port":5353,"protocol":"udp","from":"mesh","why":"the lab's names"}],
+		"zone":{"name":"${setting:zone}","listen":"web"}}`))
+	if err == nil || !strings.Contains(err.Error(), `has no listen of that name`) {
+		t.Fatalf("a zone answered by a listen the module does not have was accepted: %v", err)
+	}
+	if _, err := ParseManifest([]byte(`{"module":"lab","version":"1",
+		"listens":[{"name":"dns","port":5353,"protocol":"udp","from":"mesh","why":"the lab's names"}],
+		"zone":{"name":"${setting:zone}","listen":"dns"}}`)); err != nil {
+		t.Fatalf("a well-formed zone was refused: %v", err)
+	}
+}
+
+// The zone is the operator's (a setting) and the port is where this machine publishes the listen —
+// neither is the definition's to state.
+func TestAZoneIsPlacedFromTheNodesSettingAndPublishedPort(t *testing.T) {
+	m := Manifest{Module: "lab", Zone: &Zone{Name: "${setting:zone}", Listen: "dns"},
+		Listens: []Listening{{Name: "dns", Port: 5353, From: FromMesh}}}
+	z, err := ZoneOn(m, []Layer{{From: "node", Values: map[string]any{"zone": "Incus."}}},
+		map[int]int{5353: 15353}, "workstation", "10.77.0.3")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if z.Zone != "incus" || z.Address != "10.77.0.3" || z.Port != 15353 || z.Node != "workstation" {
+		t.Fatalf("the zone was placed as %+v", *z)
+	}
+	if _, err := ZoneOn(m, nil, nil, "workstation", "10.77.0.3"); err == nil {
+		t.Fatal("a zone nobody named was placed")
+	}
+}
+
+// One module answers a zone, and none may shadow the mesh's names or a public domain.
+func TestTheMeshRefusesAZoneTwiceOrOneThatShadows(t *testing.T) {
+	one := ZoneAt{Zone: "incus", Node: "workstation", Module: "lab", Address: "10.77.0.3", Port: 53}
+	if p := ZonesProblems([]ZoneAt{one}, "internal", []string{"example.tld"}); len(p) != 0 {
+		t.Fatalf("one ordinary zone was refused: %v", p)
+	}
+	twice := one
+	twice.Node, twice.Module = "laptop", "other"
+	cases := map[string][]ZoneAt{
+		"declared by":       {one, twice},
+		"mesh's own suffix": {{Zone: "lab.internal", Node: "a", Module: "m"}},
+		"public domain":     {{Zone: "dev.example.tld", Node: "a", Module: "m"}},
+	}
+	for want, zones := range cases {
+		p := strings.Join(ZonesProblems(zones, "internal", []string{"example.tld"}), "\n")
+		if !strings.Contains(p, want) {
+			t.Errorf("not refused for %q: %q", want, p)
+		}
+	}
+}
+
+// The resolver's template sees every zone with where it is answered, in zone order.
+func TestTheResolversTemplateRangesTheZones(t *testing.T) {
+	m := Manifest{Module: "dnsmasq", Facts: map[string]RosterFile{"zones": {
+		Path:     "/etc/mesh-resolver/zones.conf",
+		Template: "{{range .Zones}}server=/{{.Zone}}/{{.Address}}#{{.Port}}\n{{end}}",
+	}}}
+	out, err := FactsWithZonesInto(m, Resolution{Node: "anchor"}, nil, nil, nil, "", []ZoneAt{
+		{Zone: "zeta", Address: "10.77.0.2", Port: 53},
+		{Zone: "incus", Address: "10.77.0.3", Port: 15353},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := out[0]["content"]; got != "server=/incus/10.77.0.3#15353\nserver=/zeta/10.77.0.2#53\n" {
+		t.Fatalf("the resolver was told %q", got)
+	}
+}