Occassional "transport: Error while dialing only one connection allowed" errors

Start by reproducing the reported docker build -t docker-cli-dev -f ./dockerfiles/Dockerfile.dev . failure and inspect the gRPC session setup shown in the logs. No source file or test is identified, and reproduction is intermittent; done would mean identifying the cause of the single-connection dialing error and adding a verified fix or regression coverage.

Don't have a way to reproduce, but this happened to me on a couple of occasions when building the docker/cli repository;

docker build  -t docker-cli-dev -f ./dockerfiles/Dockerfile.dev .
[+] Building 0.0s (2/2) FINISHED                                                                                                                                                                                        
 => ERROR [internal] load .dockerignore                                                                                                                                                                            0.0s
 => => transferring context:                                                                                                                                                                                       0.0s
 => ERROR [internal] load build definition from Dockerfile.dev                                                                                                                                                     0.0s
 => => transferring dockerfile:                                                                                                                                                                                    0.0s
------
 > [internal] load .dockerignore:
------
------
 > [internal] load build definition from Dockerfile.dev:
------
failed to resolve dockerfile: rpc error: code = Unavailable desc = all SubConns are in TransientFailure, latest connection error: connection error: desc = "transport: Error while dialing only one connection allowed"
make: *** [build_docker_image] Error 1

Logs that look to be related to this;

=u80j74ehsqre5zenxww4x0mvx sessionID=u80j74ehsqre5zenxww4x0mvx
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.054243261Z" level=debug msg="Calling GET /_ping"
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.060894052Z" level=debug msg="Calling POST /session"
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.062535801Z" level=info msg="parsed scheme: \"\"" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.062582397Z" level=info msg="scheme \"\" not registered, fallback to default scheme" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.062769002Z" level=info msg="ccResolverWrapper: sending new addresses to cc: [{ 0  <nil>}]" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.062787116Z" level=info msg="ClientConn switching balancer to \"pick_first\"" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.062866517Z" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc43b62c1a0, CONNECTING" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.063982801Z" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc43b62c1a0, READY" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.064010389Z" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc43b62c1a0, TRANSIENT_FAILURE" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.064023179Z" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc43b62c1a0, CONNECTING" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.065463930Z" level=warning msg="grpc: addrConn.createTransport failed to connect to { 0  <nil>}. Err :connection error: desc = \"transport: Error while dialing only one connection allowed\". Reconnecting..." module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.065531653Z" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc43b62c1a0, TRANSIENT_FAILURE" module=grpc
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.069936740Z" level=debug msg="Calling POST /v1.39/build?buildargs=%7B%7D&buildid=13fd68bf24a3e4796d9464b9f458f6711400bffb06ba84b4daaa743cff31ea1d&cachefrom=%5B%5D&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile.dev&labels=%7B%7D&memory=0&memswap=0&networkmode=default&remote=client-session&rm=1&session=2tf3kj212c1fiq66nib001m2a&shmsize=0&t=docker-cli-dev&target=&ulimits=null&version=2"
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.083537626Z" level=debug msg="reusing ref for local: jlv21o58mudf9vdykymxq6cxj"
2018-12-11T11:20:55Z docker time="2018-12-11T11:20:55.097137031Z" level=debug msg="reusing ref for local: 69b5pv1cz6iuauwilmaxmruof"

Docker version;

Client: Docker Engine - Community
 Version:           18.09.0
 API version:       1.39
 Go version:        go1.10.4
 Git commit:        4d60db4
 Built:             Wed Nov  7 00:47:43 2018
 OS/Arch:           darwin/amd64
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          18.09.0
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.4
  Git commit:       4d60db4
  Built:            Wed Nov  7 00:55:00 2018
  OS/Arch:          linux/amd64
  Experimental:     true

Docker info

Containers: 14
 Running: 2
 Paused: 0
 Stopped: 12
Images: 144
Server Version: 18.09.0
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host ipvlan macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: active
 NodeID: g5l8yjyurr8xpie3k9xb08uqz
 Is Manager: true
 ClusterID: jrnii2o76lmneq8jrt9nz72ye
 Managers: 1
 Nodes: 1
 Default Address Pool: 10.0.0.0/8  
 SubnetSize: 24
 Orchestration:
  Task History Retention Limit: 5
 Raft:
  Snapshot Interval: 10000
  Number of Old Snapshots to Retain: 0
  Heartbeat Tick: 1
  Election Tick: 10
 Dispatcher:
  Heartbeat Period: 5 seconds
 CA Configuration:
  Expiry Duration: 3 months
  Force Rotate: 0
 Autolock Managers: false
 Root Rotation In Progress: false
 Node Address: 192.168.65.3
 Manager Addresses:
  192.168.65.3:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.125-linuxkit
Operating System: Docker for Mac
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 1.952GiB
Name: linuxkit-025000000001
ID: L3VR:6SGF:FS5T:YB7O:7IJZ:IOK3:2F2I:73K6:M5MP:55PZ:YDMN:YHUT
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 54
 Goroutines: 199
 System Time: 2018-12-11T11:30:49.96729541Z
 EventsListeners: 4
HTTP Proxy: gateway.docker.internal:3128
HTTPS Proxy: gateway.docker.internal:3129
Registry: https://index.docker.io/v1/
Labels:
Experimental: true
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false
Product License: Community Engine