Execute PLAN_AGGREGATOR.md

cmd/aggregator/subscriber.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"context"
+	"log"
+	"time"
+
+	pb "git.ipng.ch/ipng/nginx-logtail/proto/logtailpb"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+// CollectorSub maintains a persistent StreamSnapshots connection to one
+// collector. It reconnects with exponential backoff on any error and marks
+// the collector degraded (zeroing its contribution) after 3 consecutive
+// failures.
+type CollectorSub struct {
+	addr   string
+	merger *Merger
+}
+
+func NewCollectorSub(addr string, merger *Merger) *CollectorSub {
+	return &CollectorSub{addr: addr, merger: merger}
+}
+
+// Run blocks until ctx is cancelled.
+func (cs *CollectorSub) Run(ctx context.Context) {
+	backoff := 100 * time.Millisecond
+	const maxBackoff = 30 * time.Second
+	fails := 0
+	degraded := false
+
+	for {
+		if ctx.Err() != nil {
+			return
+		}
+
+		gotOne, err := cs.stream(ctx)
+
+		if ctx.Err() != nil {
+			return
+		}
+
+		if gotOne && degraded {
+			// Recovered: contribution is already flowing in again via Apply.
+			degraded = false
+			fails = 0
+			backoff = 100 * time.Millisecond
+			log.Printf("subscriber: collector %s recovered", cs.addr)
+		}
+
+		if err != nil {
+			fails++
+			log.Printf("subscriber: collector %s error (fail %d): %v", cs.addr, fails, err)
+			if fails >= 3 && !degraded {
+				degraded = true
+				cs.merger.Zero(cs.addr)
+				log.Printf("subscriber: collector %s degraded — contribution zeroed", cs.addr)
+			}
+		}
+
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(backoff):
+		}
+		backoff = min(backoff*2, maxBackoff)
+	}
+}
+
+// stream opens a single StreamSnapshots RPC and feeds snapshots into the
+// merger until the stream errors or ctx is cancelled. Returns (gotAtLeastOne, err).
+func (cs *CollectorSub) stream(ctx context.Context) (bool, error) {
+	conn, err := grpc.NewClient(cs.addr,
+		grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		return false, err
+	}
+	defer conn.Close()
+
+	client := pb.NewLogtailServiceClient(conn)
+	stream, err := client.StreamSnapshots(ctx, &pb.SnapshotRequest{})
+	if err != nil {
+		return false, err
+	}
+
+	log.Printf("subscriber: connected to collector %s", cs.addr)
+	gotOne := false
+	for {
+		snap, err := stream.Recv()
+		if err != nil {
+			return gotOne, err
+		}
+		gotOne = true
+		cs.merger.Apply(snap)
+	}
+}