Receive: fix capnproto replication in endless loop

CHANGELOG.md

@@ -10,6 +10,10 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 ## Unreleased
 
+### Fixed
+
+- [#8254](https://github.com/thanos-io/thanos/issues/8254) Receive: Endless loop of retried replication with capnproto and distributors
+
 ## [v0.40.0](https://github.com/thanos-io/thanos/tree/release-0.40) - 2025 10 20 (in progress)
 
 ### Fixed
@@ -22,22 +26,21 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 - [#8366](https://github.com/thanos-io/thanos/pull/8366) Store: optionally ignore Parquet migrated blocks
 - [#8359](https://github.com/thanos-io/thanos/pull/8359) Tools: add `--shipper.upload-compacted` flag for uploading compacted blocks to bucket upload-blocks
-- [#8484](https://github.com/thanos-io/thanos/pull/8484) Query: add `/api/v1/status/tsdb` API endpoint.
 
 ### Changed
 
 - [#8370](https://github.com/thanos-io/thanos/pull/8370) Query: announced labelset now reflects relabel-config
 
 ### Removed
 
-## [v0.39.2](https://github.com/thanos-io/thanos/tree/release-0.39) - 2025 07 17
+### [v0.39.2](https://github.com/thanos-io/thanos/tree/release-0.39) - 2025 07 17
 
 ### Fixed
 
 - [#8374](https://github.com/thanos-io/thanos/pull/8374) Query: fix panic when concurrently accessing annotations map
 - [#8375](https://github.com/thanos-io/thanos/pull/8375) Query: fix native histogram buckets in distributed queries
 
-## [v0.39.1](https://github.com/thanos-io/thanos/tree/release-0.39) - 2025 07 01
+### [v0.39.1](https://github.com/thanos-io/thanos/tree/release-0.39) - 2025 07 01
 
 Fixes a memory leak issue on query-frontend. The bug only affects v0.39.0.
 

pkg/receive/writecapnp/client.go

@@ -117,17 +117,28 @@ func (r *RemoteWriteClient) connect(ctx context.Context) error {
 		return errors.Wrap(err, "failed to dial peer")
 	}
 	r.conn = rpc.NewConn(rpc.NewPackedStreamTransport(conn), nil)
-	r.writer = Writer(r.conn.Bootstrap(ctx))
+	writer := Writer(r.conn.Bootstrap(ctx))
+	if err := writer.Resolve(ctx); err != nil {
+		level.Warn(r.logger).Log("msg", "failed to bootstrap capnp writer, closing connection", "err", err)
+		r.closeUnlocked()
+		return errors.Wrap(err, "failed to bootstrap capnp writer")
+	}
+
+	r.writer = writer
 	return nil
 }
 
 func (r *RemoteWriteClient) Close() error {
 	r.mu.Lock()
+	r.closeUnlocked()
+	r.mu.Unlock()
+	return nil
+}
+
+func (r *RemoteWriteClient) closeUnlocked() {
 	if r.conn != nil {
 		conn := r.conn
 		r.conn = nil
 		go conn.Close()
 	}
-	r.mu.Unlock()
-	return nil
 }