Curling docker.local after running nginx container hangs for ~5 seconds

Docker Desktop
1

Expected behavior

After running docker run -d -p 80:80 nginx, curl docker.local should respond in a reasonable amount of time.

Actual behavior

curl docker.local consistently hangs for around 5 seconds. Some other potentially relevant things:

  • ping docker.local: perfoms normally
  • ping 192.168.64.2: performs normally
  • curl 192.168.64.2: performs normally (name resolution problems?)
  • nc -z docker.local 80: hangs for 5 seconds then succeeds
  • nc -z 192.168.64.2 80: performs normally

Information

  • pinata diagnose -u:
OS X: version 10.11.4 (build: 15E65)
Docker.app: version v1.11.0-beta8.2
Running diagnostic tests:
[OK]      docker-cli
[OK]      Moby booted
[OK]      driver.amd64-linux
[OK]      vmnetd
[OK]      osxfs
[OK]      db
[OK]      slirp
[OK]      menubar
[OK]      environment
[OK]      Docker
[OK]      VT-x
Docker logs are being collected into /tmp/20160428-141528.tar.gz
Most specific failure is: No error was detected
Your unique id is: 0E586D17-BE5B-4D6E-ABC4-54F06F25DFE7
Please quote this in all correspondence.

Steps to reproduce the behavior

  1. Install Docker for Mac beta.
  2. Run docker run -d -p 80:80 nginx
  3. Run curl docker.local
2

Digging into this more with tcpdump, it does indeed appear that it has something to do with dns cacheing—when the request is made with curl, there’s 5 seconds worth of mDNS traffic before the HTTP request goes out, whereas in the browser, this does not happen, presumably due to browser-internal DNS cacheing. Now that I think about it, I remember the browser hanging for 5 seconds the very first time I used it to make a request to docker.local. Also plausibly related is this cryptic blog post. I’m going to dig into it more and see if I can figure out exactly what’s wrong with mDNS.

3

Here is a tcpdump of what happens during the curl, in case it’s interesting:

16:15:35.536113 IP 192.168.64.1.mdns > 224.0.0.251.mdns: 0 [2q] A (QU)? docker.local. AAAA (QU)? docker.local. (36)
16:15:35.536522 IP 192.168.64.2.mdns > 192.168.64.1.mdns: 0*- [0q] 1/0/0 A 192.168.64.2 (40)
16:15:36.614929 IP 192.168.64.1.mdns > 224.0.0.251.mdns: 0 [1a] [2q] A (QM)? docker.local. AAAA (QM)? docker.local. (52)
16:15:36.615467 IP 192.168.64.2.mdns > 192.168.64.1.mdns: 0*- [0q] 1/0/0 A 192.168.64.2 (40)
16:15:38.988901 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [S], seq 577689276, win 65535, options [mss 1460,nop,wscale 5,nop,nop,TS val 1139119169 ecr 0,sackOK,eol], length 0
16:15:38.989408 IP 192.168.64.2.http > 192.168.64.1.60646: Flags [S.], seq 66653052, ack 577689277, win 28960, options [mss 1460,sackOK,TS val 1018688 ecr 1139119169,nop,wscale 7], length 0
16:15:38.989447 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [.], ack 1, win 4117, options [nop,nop,TS val 1139119169 ecr 1018688], length 0
16:15:38.989515 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [P.], seq 1:77, ack 1, win 4117, options [nop,nop,TS val 1139119169 ecr 1018688], length 76: HTTP: GET / HTTP/1.1
16:15:38.989774 IP 192.168.64.2.http > 192.168.64.1.60646: Flags [.], ack 77, win 227, options [nop,nop,TS val 1018688 ecr 1139119169], length 0
16:15:38.989923 IP 192.168.64.2.http > 192.168.64.1.60646: Flags [P.], seq 1:239, ack 77, win 227, options [nop,nop,TS val 1018688 ecr 1139119169], length 238: HTTP: HTTP/1.1 200 OK
16:15:38.989949 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [.], ack 239, win 4110, options [nop,nop,TS val 1139119170 ecr 1018688], length 0
16:15:38.990010 IP 192.168.64.2.http > 192.168.64.1.60646: Flags [P.], seq 239:851, ack 77, win 227, options [nop,nop,TS val 1018688 ecr 1139119169], length 612: HTTP
16:15:38.990029 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [.], ack 851, win 4091, options [nop,nop,TS val 1139119170 ecr 1018688], length 0
16:15:38.990163 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [F.], seq 77, ack 851, win 4096, options [nop,nop,TS val 1139119170 ecr 1018688], length 0
16:15:38.990460 IP 192.168.64.2.http > 192.168.64.1.60646: Flags [F.], seq 851, ack 78, win 227, options [nop,nop,TS val 1018688 ecr 1139119170], length 0
16:15:38.990627 IP 192.168.64.1.60646 > 192.168.64.2.http: Flags [.], ack 852, win 4096, options [nop,nop,TS val 1139119170 ecr 1018688], length 0
4

Whoops, apparently this is a dup of Slow IP resolution of docker container. Also docker.local is not a thing anymore in beta9 anyway :slight_smile: