{"record":{"id":"614e3d239ebdbc7b","repo":"hashicorp/nomad","slug":"failed-to-open-a-streaming-connection-v","errorCode":null,"errorMessage":"failed to open a streaming connection: %v","messagePattern":"failed to open a streaming connection: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"helper/pool/pool.go","lineNumber":501,"sourceCode":"\t\t\tretries++\n\t\t\tgoto START\n\t\t}\n\t\treturn nil, nil, fmt.Errorf(\"failed to start stream: %v\", err)\n\t}\n\treturn conn, client, nil\n}\n\n// StreamingRPC is used to make an streaming RPC call.  Callers must\n// close the connection when done.\nfunc (p *ConnPool) StreamingRPC(region string, addr net.Addr) (net.Conn, error) {\n\tconn, err := p.acquire(region, addr)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to get conn: %v\", err)\n\t}\n\n\ts, err := conn.session.Open()\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to open a streaming connection: %v\", err)\n\t}\n\n\tif _, err := s.Write([]byte{byte(RpcStreaming)}); err != nil {\n\t\tconn.Close()\n\t\treturn nil, err\n\t}\n\n\treturn s, nil\n}\n\n// RPC is used to make an RPC call to a remote host\nfunc (p *ConnPool) RPC(region string, addr net.Addr, method string, args interface{}, reply interface{}) error {\n\t// Get a usable client\n\tconn, sc, err := p.getRPCClient(region, addr)\n\tif err != nil {\n\t\treturn fmt.Errorf(\"rpc error: %w\", err)\n\t}\n\tdefer conn.releaseUse()","sourceCodeStart":483,"sourceCodeEnd":519,"githubUrl":"https://github.com/hashicorp/nomad/blob/482b49bf1aec006f089bcfc7e632d8f6ac303e5e/helper/pool/pool.go#L483-L519","documentation":"After acquiring a conn, StreamingRPC opens a yamux stream on the connection's session. If session.Open fails, the error is wrapped as 'failed to open a streaming connection: <err>'. The connection is a TCP session multiplexed via yamux; opening a new stream can fail if the underlying session died.","triggerScenarios":"pool.StreamingRPC where conn.session.Open() errors — typically because the pooled TCP connection was closed/reset by the peer between acquire and open.","commonSituations":"Idle pooled connection silently dropped by the server or a NAT/load balancer; agent restart closing the session; yamux window exhaustion under load.","solutions":["Retry the StreamingRPC call; a fresh connection will be dialed after the dead one is cleared","Check for NAT/firewall idle timeouts killing long-lived TCP sessions","Verify the target agent hasn't restarted (sessions die on restart)","Check server logs for connection resets around the failure time"],"exampleFix":null,"handlingStrategy":"retry","validationCode":null,"typeGuard":null,"tryCatchPattern":"conn, err := pool.StreamingRPC(region, addr)\nif err != nil && strings.Contains(err.Error(), \"failed to open a streaming connection\") {\n    // stale yamux session; retrying dials a fresh connection\n    time.Sleep(100 * time.Millisecond)\n    conn, err = pool.StreamingRPC(region, addr)\n}\nif err != nil { return err }\ndefer conn.Close()","preventionTips":["Tune NAT/firewall idle timeouts above the connection keepalive interval","Retry streaming opens once — dead pooled conns are refreshed on retry","Detect agent restarts and re-establish streams instead of reusing them"],"tags":["rpc","yamux","streaming"],"backgroundTag":"rpc-stream-setup-failed","analyzedSha":"482b49bf1aec006f089bcfc7e632d8f6ac303e5e","analyzedAt":"2026-09-04T07:54:14.808Z","contentChangedAt":"2026-09-04T07:54:14.808Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}