Moving app to docker from host increases HTTP lag by 5 seconds

I have an app that I noticed was performing badly when making outgoing HTTP requests (an extra lag of 5 seconds). Through a lot of trials / tests, I realized that moving the app outside of docker into the host machine eliminated the weird HTTP lag.

I'm using alpine linux for the docker image, and ubuntu is hosting the parent machine.

Docker Info:

Docker version 1.11.2, build b9f10c9

      "NetworkSettings": {
        "Bridge": "",
        "SandboxID": "3ab81b8a66a99c6e9b1a1f49c5410d8260db37eee96c9231c0d83c1b40f84fa5",
        "HairpinMode": false,
        "LinkLocalIPv6Address": "",
        "LinkLocalIPv6PrefixLen": 0,
        "Ports": {
            "8084/tcp": null
        },
        "SandboxKey": "/var/run/docker/netns/3ab81b8a66a9",
        "SecondaryIPAddresses": null,
        "SecondaryIPv6Addresses": null,

        "EndpointID": "464acfb299941bbd301051ea05451823a7e527161185570c00f8569ce2afde88",
        "Gateway": "172.17.0.1",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "IPAddress": "172.17.0.3",
        "IPPrefixLen": 16,
        "IPv6Gateway": "",
        "MacAddress": "02:42:ac:11:00:03",
        "Networks": {
            "bridge": {
                "IPAMConfig": null,
                "Links": null,
                "Aliases": null,
                "NetworkID": "32ebc75bc4c98106c6775905906723405c58bc3de914283234a8e1273cba7193",
                "EndpointID": "464acfb299941bbd301051ea05451823a7e527161185570c00f8569ce2afde88",

                "Gateway": "172.17.0.1",
                "IPAddress": "172.17.0.3",
                "IPPrefixLen": 16,
                "IPv6Gateway": "",
                "GlobalIPv6Address": "",
                "GlobalIPv6PrefixLen": 0,
                "MacAddress": "02:42:ac:11:00:03"
            }
        }
    }

I ran the docker container without anything fancy:

docker run -d test

My code (python) times how long it takes for the whole request cycle:

now = datetime.now()
response = http.request('POST', url, body=request_body, headers=headers)

print(
    "nTotal Time: ",
    (datetime.now() - now).total_seconds()
)

The constant times are 5-6 seconds, where outside the container, its less than once second.

I did a drill to check DNS and a tcpdump from inside the container. The doesn't seem to be anything interesting to report from there. DNS looks fine, and the packet captures report 0.2 sec requests times.

The only interesting thing I found from the packet capture was that it took 5 seconds to see the beginning of the packet from when the http.request was called.

I'm convinced there is a docker networking misconfiguration here somewhere. Please let me know if there any more information I need to add. We are using docker for 20 other services without this problem.

Thanks!