cmd/mesh-controller/plans_one_at_a_time_test.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"testing"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// novox/hq issue 213: for the moment a machine hands its controller over, the container and the
+// process both run the plan timer on one store. Only the one holding the plans moves them; the other
+// leaves them alone, and moves them once they are let go.
+func TestAControllerLeavesThePlansToTheOneHoldingThem(t *testing.T) {
+	open := aMesh(t)
+	ctx := t.Context()
+	now := time.Now().UTC()
+	// Every tier done: the next step is the plan's last, and needs nothing but the store.
+	plan := inventory.Plan{ID: "plan-213", Repository: "r", Commit: "abc", Created: now, Updated: now,
+		State: inventory.PlanRolling, Tier: 1, Tiers: [][]string{{"app"}},
+		Modules: map[string]*inventory.PlanModule{"app": {State: "built"}}}
+	if err := open.inventory.SavePlan(ctx, plan); err != nil {
+		t.Fatal(err)
+	}
+
+	// The other controller: its own connections to the same store, holding the plans.
+	other, err := inventory.Open(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(other.Close)
+	release, err := other.HoldPlans(ctx, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(release) // before the close above: a pool waits for a connection still held
+
+	advancePlans(ctx, open)
+	if p, err := open.inventory.PlanByID(ctx, "plan-213"); err != nil || !p.Open() {
+		t.Fatalf("a controller moved a plan another held: %+v %v", p, err)
+	}
+
+	release()
+	advancePlans(ctx, open)
+	if p, err := open.inventory.PlanByID(ctx, "plan-213"); err != nil || p.State != inventory.PlanDone {
+		t.Fatalf("the plan did not move once it was let go: %+v %v", p, err)
+	}
+}

cmd/mesh-controller/release_plan.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"sort"
@@ -296,6 +297,15 @@ func askTier(ctx context.Context, inv *inventory.Inventory, p *inventory.Plan) e
 // build's request time is not known, and such an outcome is taken as before.
 func planBuilt(ctx context.Context, open *stores, module, commit, failed string, asked time.Time) {
 	inv := open.inventory
+	// One controller works the plans at a time (novox/hq issue 213); an outcome waits its turn rather
+	// than write over what the holder is about to save. Not taken, it is still in the build records,
+	// which the holder settles the plan from (issue 214).
+	release, err := inv.HoldPlans(ctx, true)
+	if err != nil {
+		fmt.Printf("plans: %s's outcome is left to the build records: %v\n", module, err)
+		return
+	}
+	defer release()
 	plans, err := inv.OpenPlans(ctx)
 	if err != nil {
 		fmt.Printf("plans: cannot read them: %v\n", err)
@@ -342,13 +352,30 @@ func planBuilt(ctx context.Context, open *stores, module, commit, failed string,
 			fmt.Printf("%s: %s; the tiers after it are not asked\n", p.ID, p.Note)
 		}
 	}
-	advancePlans(ctx, open)
+	advanceHeld(ctx, open)
 }
 
 // advancePlans moves every open plan as far as the facts allow: a tier whose modules are all built
 // and whose gates are applied gives way to the next; the last tier done is the plan done. Called
 // after every outcome and on a timer, so a plan waiting on a machine's report moves when it comes.
+//
+// **One controller at a time** (novox/hq issue 213). A plan is read, changed and saved whole; two
+// controllers — the old and the new while a machine hands its controller over — would each ask a
+// tier the other had just asked. Taken without waiting: whoever holds the plans is moving them.
 func advancePlans(ctx context.Context, open *stores) {
+	release, err := open.inventory.HoldPlans(ctx, false)
+	if err != nil {
+		if !errors.Is(err, inventory.ErrPlansBusy) {
+			fmt.Printf("plans: cannot hold them: %v\n", err)
+		}
+		return
+	}
+	defer release()
+	advanceHeld(ctx, open)
+}
+
+// advanceHeld is advancePlans for a caller already holding the plans.
+func advanceHeld(ctx context.Context, open *stores) {
 	inv := open.inventory
 	plans, err := inv.OpenPlans(ctx)
 	if err != nil {
@@ -676,6 +703,19 @@ func plansCommand(ctx context.Context, args []string) error {
 		}
 		p.State = inventory.PlanFailed
 		p.Note = "stopped by hand at tier " + fmt.Sprint(p.Tier)
+		release, err := inv.HoldPlans(ctx, true)
+		if err != nil {
+			return err
+		}
+		defer release()
+		if p, err = inv.PlanByID(ctx, positionals[1]); err != nil {
+			return err
+		}
+		if !p.Open() {
+			return fmt.Errorf("%s is already %s", p.ID, p.State)
+		}
+		p.State = inventory.PlanFailed
+		p.Note = "stopped by hand at tier " + fmt.Sprint(p.Tier)
 		if err := inv.SavePlan(ctx, p); err != nil {
 			return err
 		}

cmd/mesh-controller/upgrades.go

@@ -315,6 +315,13 @@ func (f following) SourceMoved(ctx context.Context, m link.SourceMoved) error {
 	for _, e := range moved {
 		movedNames = append(movedNames, e.Manifest.Module)
 	}
+	// Written and its first tier asked as one act on the plans (novox/hq issue 213): a timer on
+	// another controller reading it between the two would ask the tier again.
+	release, err := inv.HoldPlans(ctx, true)
+	if err != nil {
+		return notNow(err)
+	}
+	defer release()
 	plan := planOfMerge(m, movedNames, edges)
 	if hasCycle(plan.Tiers, edges) {
 		fmt.Printf("  the last tier depends on itself: %s — built together, in no order\n",

internal/inventory/hold.go

@@ -87,3 +87,62 @@ func (i *Inventory) tryHold(ctx context.Context, sorted []string) (func(), strin
 	}
 	return release, "", nil
 }
+
+// ErrPlansBusy is the plans held by another act — on a machine replacing its controller, the other
+// controller — for longer than a caller waits, or at all for one that does not wait.
+var ErrPlansBusy = errors.New("another controller is working the plans")
+
+// HoldPlans makes working the plans one act at a time, across every controller on the store
+// (novox/hq issue 213). A plan is read, changed and written whole; two controllers doing that at
+// once — the old and the new for the moment a machine hands its controller over, or a controller
+// and a person's `plans stop` — each act on what the other has not saved yet: a tier asked twice,
+// an outcome written over. A session-level advisory lock on one connection, released by the
+// returned function and by the session ending, so a controller that dies holding it holds nothing.
+//
+// wait false gives ErrPlansBusy at once when another holds them — the timer's way: the holder is
+// moving the plans already. wait true looks again every HoldPoll for up to HoldWaitFor — an
+// outcome's or a merge's way, which must be written.
+func (i *Inventory) HoldPlans(ctx context.Context, wait bool) (func(), error) {
+	deadline := time.Now().Add(HoldWaitFor)
+	for {
+		release, took, err := i.tryLock(ctx, "mesh-plans")
+		if err != nil || took {
+			return release, err
+		}
+		if !wait || time.Now().After(deadline) {
+			return nil, ErrPlansBusy
+		}
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-time.After(HoldPoll):
+		}
+	}
+}
+
+// tryLock takes one named advisory lock on a connection of its own, or gives the connection back.
+func (i *Inventory) tryLock(ctx context.Context, key string) (func(), bool, error) {
+	conn, err := i.store.Pool().Acquire(ctx)
+	if err != nil {
+		return nil, false, err
+	}
+	var once sync.Once
+	release := func() {
+		once.Do(func() {
+			if _, err := conn.Exec(context.WithoutCancel(ctx), `select pg_advisory_unlock_all()`); err != nil {
+				_ = conn.Conn().Close(context.WithoutCancel(ctx))
+			}
+			conn.Release()
+		})
+	}
+	var took bool
+	if err := conn.QueryRow(ctx, `select pg_try_advisory_lock(hashtext($1)::bigint)`, key).Scan(&took); err != nil {
+		release()
+		return nil, false, err
+	}
+	if !took {
+		release()
+		return nil, false, nil
+	}
+	return release, true, nil
+}

internal/inventory/hold_plans_test.go

@@ -0,0 +1,38 @@
+package inventory
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+// novox/hq issue 213: while a machine hands its controller over from the container to the process,
+// two controllers run on one store for a moment. Working the plans is one act at a time across them.
+func TestThePlansAreWorkedByOneControllerAtATime(t *testing.T) {
+	first := ForTest(t)
+	// A second controller: its own connections to the same store.
+	second, err := Open(t.Context())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(second.Close)
+
+	release, err := first.HoldPlans(t.Context(), false)
+	if err != nil {
+		t.Fatalf("the plans could not be held when nobody held them: %v", err)
+	}
+	t.Cleanup(release) // a pool closing waits for a connection still held; release is idempotent
+	if _, err := second.HoldPlans(t.Context(), false); !errors.Is(err, ErrPlansBusy) {
+		t.Fatalf("a second controller held the plans while the first did: %v", err)
+	}
+	// A waiter gets them once they are let go.
+	was := HoldPoll
+	HoldPoll = 10 * time.Millisecond
+	defer func() { HoldPoll = was }()
+	go func() { time.Sleep(50 * time.Millisecond); release() }()
+	again, err := second.HoldPlans(t.Context(), true)
+	if err != nil {
+		t.Fatalf("a waiting controller never got the plans once they were let go: %v", err)
+	}
+	again()
+}

internal/link/receive_nats.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"log"
 	"strings"
 	"time"
 
@@ -78,10 +79,15 @@ func (n *natsInbound) Receive(ctx context.Context, act func(context.Context, Con
 	// than creating one here: the consumer is an object with a configuration — ack policy, ack
 	// wait, redelivery — and a client that creates its own would be a second opinion about it.
 	control := make(chan *nats.Msg, Prefetch)
-	said, err := js.ChanSubscribe("", control, nats.Bind("CONTROL", broker.ControllerName))
+	said, err := standingBy(ctx, log.Default(), "CONTROL", func() (*nats.Subscription, error) {
+		return js.ChanSubscribe("", control, nats.Bind("CONTROL", broker.ControllerName))
+	})
 	if err != nil {
 		return fmt.Errorf("subscribing to what nodes say: %w", err)
 	}
+	if said == nil {
+		return nil // stopped while standing by
+	}
 	defer func() { _ = said.Unsubscribe() }()
 
 	// Heartbeats, on core NATS and off any stream (design 25 §3). Their own subscription because
@@ -97,10 +103,15 @@ func (n *natsInbound) Receive(ctx context.Context, act func(context.Context, Con
 	var events chan *nats.Msg
 	if len(n.follows) > 0 {
 		events = make(chan *nats.Msg, Prefetch)
-		followed, err := js.ChanSubscribe("", events, nats.Bind("EVENTS", broker.ControllerName))
+		followed, err := standingBy(ctx, log.Default(), "EVENTS", func() (*nats.Subscription, error) {
+			return js.ChanSubscribe("", events, nats.Bind("EVENTS", broker.ControllerName))
+		})
 		if err != nil {
 			return fmt.Errorf("subscribing to what the catalogue says: %w", err)
 		}
+		if followed == nil {
+			return nil
+		}
 		defer func() { _ = followed.Unsubscribe() }()
 	}
 
@@ -324,3 +335,44 @@ func (m *natsControl) forget() {
 type replyAddressed struct {
 	ReplyTo string `json:"reply_to,omitempty"`
 }
+
+// StandbyPoll is how often a controller standing by looks again for its consumers. A variable so a
+// test need not wait.
+var StandbyPoll = 2 * time.Second
+
+// standingBy binds one of the controller's consumers, waiting while another controller holds it.
+//
+// **Two controllers, one consumer** (novox/hq issue 213). The controller's consumers are push
+// consumers with no delivery group, so the server lets one subscription bind each — on purpose:
+// two would each act on every message (issue 146). When a machine hands its controller over from
+// the container to the process, the host starts the process first and removes the container only
+// once the process is up; the process then finds the consumers bound. Exiting on that would never
+// be up, so the container would never go. It stands by instead — the seat's verbs are already
+// served from a queue group, and the plans wait on their lock — and binds as soon as the other lets
+// go. Nil and no error is ctx ending while it waited.
+func standingBy(ctx context.Context, logger interface{ Printf(string, ...any) }, stream string,
+	bind func() (*nats.Subscription, error)) (*nats.Subscription, error) {
+	said := false
+	for {
+		sub, err := bind()
+		if err == nil {
+			if said {
+				logger.Printf("took the controller's consumer on %s: the controller that held it let go", stream)
+			}
+			return sub, nil
+		}
+		if !strings.Contains(err.Error(), "already bound") {
+			return nil, err
+		}
+		if !said {
+			logger.Printf("another controller holds the controller's consumer on %s; standing by "+
+				"until it lets go", stream)
+			said = true
+		}
+		select {
+		case <-ctx.Done():
+			return nil, nil
+		case <-time.After(StandbyPoll):
+		}
+	}
+}

internal/link/standby_nats_test.go

@@ -0,0 +1,69 @@
+package link
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/broker"
+)
+
+// novox/hq issue 213: while a machine hands its controller over, the new controller (the process)
+// is started while the old one (the container) still holds the controller's consumers. It must not
+// exit — the host would read that as a replacement that did not come up and never remove the
+// container — and must not act on what the old one is handed. It stands by, and takes the consumers
+// when the old one lets go.
+func TestNatsASecondControllerStandsByAndTakesOverWhenTheFirstLetsGo(t *testing.T) {
+	js := aBus(t)
+	was := StandbyPoll
+	StandbyPoll = 50 * time.Millisecond
+	defer func() { StandbyPoll = was }()
+
+	old := &counted{}
+	_, stopOld := servingOn(t, js, old)
+	eventually(t, "the first controller binding its consumer", func() bool {
+		info, err := js.Context().ConsumerInfo("CONTROL", broker.ControllerName)
+		return err == nil && info.PushBound
+	})
+
+	// The new one, on a connection of its own as the process would have.
+	second, err := broker.Dial(os.Getenv("MESH_TEST_NATS"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(second.Close)
+	fresh := &counted{}
+	s := &Server{inbound: Nats(second), bus: OverNATS{Conn: second.Conn(), JS: second.Context()},
+		listener: fresh, log: quiet()}
+	ctx, stopNew := context.WithCancel(context.Background())
+	defer stopNew()
+	ended := make(chan error, 1)
+	go func() { ended <- s.Serve(ctx) }()
+
+	select {
+	case err := <-ended:
+		t.Fatalf("the second controller stopped instead of standing by: %v", err)
+	case <-time.After(500 * time.Millisecond):
+	}
+
+	report := func(declared string) {
+		body, _ := json.Marshal(Report{Node: "anchor", Declared: declared, Applied: []string{"store"}})
+		if _, err := js.Context().Publish(ReportSubject("anchor"), body); err != nil {
+			t.Fatal(err)
+		}
+	}
+	report("d1")
+	eventually(t, "the holding controller hearing the report", func() bool { return old.count() == 1 })
+	if fresh.count() != 0 {
+		t.Fatal("the controller standing by acted on a report the holder was handed")
+	}
+
+	stopOld()
+	report("d2")
+	eventually(t, "the second controller taking over once the first let go", func() bool { return fresh.count() == 1 })
+	if old.count() != 1 {
+		t.Errorf("the first controller heard %d reports", old.count())
+	}
+}