Docker attach timing bug

about.md

When starting and attaching to a container with a pseudo-tty, the initial bash prompt will only appear if the 'attach' request comes very quickly after the 'start' request (<0.1 seconds, in my tests).

Note how in the first run (attach immediately after starting), a chunk is received containing the prompt, but in the second run (start, then sleep 1s, then attach), it hangs after receiving the response headers.

This is an issue when trying to run a bash container from a Docker client that is geographically distant from the Docker server - the prompt doesn't appear, and you have to hit Enter to get one. From a UX standpoint, it appears as if Docker is simply hanging, which is pretty frustrating!

output

root@docker:~# python test.py localhost 4000 0
curl --verbose http://localhost:4000/v1.5/containers/create -d '{"Hostname":"","Domainname":"","User":"","Memory":0,"MemorySwap":0,"CpuShares":0,"AttachStdin":true,"AttachStdout":true,"AttachStderr":true,"PortSpecs":null,"Tty":true,"OpenStdin":true,"StdinOnce":true,"Env":null,"Cmd":["bash"],"Dns":null,"Image":"ubuntu","Volumes":{},"VolumesFrom":"","WorkingDir":"","Entrypoint":[],"NetworkDisabled":false,"Privileged":false}' -H 'Content-Type: application/json'

Created container 668b00739999

curl --verbose http://localhost:4000/v1.5/containers/668b00739999/start -d '{"Binds":null,"ContainerIDFile":"","LxcConf":[]}'

Sending u'POST /v1.5/containers/668b00739999/attach?logs=1&stderr=1&stdin=1&stdout=1&stream=1 HTTP/1.1\r\n\r\n'

Got chunk: 'HTTP/1.1 200 OK\r\nContent-Type: application/vnd.docker.raw-stream\r\n\r\n'

Got chunk: 'root@668b00739999:/# '

^CTraceback (most recent call last):
  File "test.py", line 42, in <module>
    chunk = s.recv(4096)
KeyboardInterrupt







root@docker:~# python test.py localhost 4000 1
curl --verbose http://localhost:4000/v1.5/containers/create -d '{"Hostname":"","Domainname":"","User":"","Memory":0,"MemorySwap":0,"CpuShares":0,"AttachStdin":true,"AttachStdout":true,"AttachStderr":true,"PortSpecs":null,"Tty":true,"OpenStdin":true,"StdinOnce":true,"Env":null,"Cmd":["bash"],"Dns":null,"Image":"ubuntu","Volumes":{},"VolumesFrom":"","WorkingDir":"","Entrypoint":[],"NetworkDisabled":false,"Privileged":false}' -H 'Content-Type: application/json'

Created container d61c1660a7d2

curl --verbose http://localhost:4000/v1.5/containers/d61c1660a7d2/start -d '{"Binds":null,"ContainerIDFile":"","LxcConf":[]}'

Sending u'POST /v1.5/containers/d61c1660a7d2/attach?logs=1&stderr=1&stdin=1&stdout=1&stream=1 HTTP/1.1\r\n\r\n'

Got chunk: 'HTTP/1.1 200 OK\r\nContent-Type: application/vnd.docker.raw-stream\r\n\r\n'

^CTraceback (most recent call last):
  File "test.py", line 42, in <module>
    chunk = s.recv(4096)
KeyboardInterrupt

test.py

import sys
import subprocess
import json
import time
import socket
from pipes import quote

argv = sys.argv[1:]

if len(argv) != 3:
    print "Usage: test.py DOCKER_HOST DOCKER_PORT SLEEP_TIME"
    exit(1)

host, port, sleep_time = argv[0], argv[1], float(argv[2])

def curl(*args):
    print " ".join(map(quote, ["curl", "--verbose"] + list(args)))
    return ["curl", "--fail", "--silent"] + list(args)

post_data = '{"Hostname":"","Domainname":"","User":"","Memory":0,"MemorySwap":0,"CpuShares":0,"AttachStdin":true,"AttachStdout":true,"AttachStderr":true,"PortSpecs":null,"Tty":true,"OpenStdin":true,"StdinOnce":true,"Env":null,"Cmd":["bash"],"Dns":null,"Image":"ubuntu","Volumes":{},"VolumesFrom":"","WorkingDir":"","Entrypoint":[],"NetworkDisabled":false,"Privileged":false}'

container_response = subprocess.check_output(curl("http://%s:%s/v1.5/containers/create" % (host, port), "-d", post_data, "-H", "Content-Type: application/json"))
print

container_id = json.loads(container_response)['Id']
print "Created container", container_id
print

subprocess.check_call(curl("http://%s:%s/v1.5/containers/%s/start" % (host, port, container_id), "-d", '{"Binds":null,"ContainerIDFile":"","LxcConf":[]}'))
print

time.sleep(sleep_time)

attach_request = "POST /v1.5/containers/%s/attach?logs=1&stderr=1&stdin=1&stdout=1&stream=1 HTTP/1.1\r\n\r\n" % container_id
print "Sending", repr(attach_request)
print

s = socket.create_connection((host, port))
s.send(attach_request)

while True:
    chunk = s.recv(4096)

    if not chunk:
        break

    print 'Got chunk:', repr(chunk)
    print