Requests with sufficiently big headers hang on hybrid swarm cluster

[riccaa]

Synopsis

On a hybrid swarm cluster (1 Ubuntu node and 1 Windows Server node) on Azure, when making an http request from a linux container (on linux node) to a windows container (on a windows node) all seems to be working fine with small size requests, but calls systematically stop working with sufficiently big headers.
Issue possibly related to the following: #41051

---

VM #1 (Windows)

• Base image : Windows Server 2019 Datacenter with containers
• Name : test-w-001
• Size : D2s v3 (https://docs.microsoft.com/en-us/azure/virtual-machines/acu)
• NIC Private IP : 10.1.0.13
• Azure VM Networking, inbound port rules : Allow for any Port, any Protocol, any Source, any Destination
• Azure VM Networking, outbound port rules : Allow for any Port, any Protocol, any Source, any Destination
• Windows update and then reboot
• Windows Defender Firewall : Disabled for Domain Profile, Private Profile, Public Profile ... And then reboot

Output of "docker version":

Client: Docker Engine - Enterprise
 Version:           19.03.5
 API version:       1.40
 Go version:        go1.12.12
 Git commit:        2ee0c57608
 Built:             11/13/2019 08:00:16
 OS/Arch:           windows/amd64
 Experimental:      false

Server: Docker Engine - Enterprise
 Engine:
  Version:          19.03.5
  API version:      1.40 (minimum version 1.24)
  Go version:       go1.12.12
  Git commit:       2ee0c57608
  Built:            11/13/2019 07:58:51
  OS/Arch:          windows/amd64
  Experimental:     false

Output of "docker info":

Client:
 Debug Mode: false
 Plugins:
  cluster: Manage Docker clusters (Docker Inc., v1.2.0)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 3
 Server Version: 19.03.5
 Storage Driver: windowsfilter
  Windows:
 Logging Driver: json-file
 Plugins:
  Volume: local
  Network: ics internal l2bridge l2tunnel nat null overlay private transparent
  Log: awslogs etwlogs fluentd gcplogs gelf json-file local logentries splunk syslog
 Swarm: inactive
 Default Isolation: process
 Kernel Version: 10.0 17763 (17763.1.amd64fre.rs5_release.180914-1434)
 Operating System: Windows Server 2019 Datacenter Version 1809 (OS Build 17763.1369)
 OSType: windows
 Architecture: x86_64
 CPUs: 2
 Total Memory: 8GiB
 Name: test-w-001
 ID: IMUI:CELM:ENKE:SJOT:KM5S:OZKW:KCSE:VJM2:CBM5:HBBZ:5RHW:2M46
 Docker Root Dir: C:\ProgramData\docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

---

VM #2 (Ubuntu)

• Base image : Ubuntu Server 18.04 LTS
• Name : test-l-001
• Size : D2s v3 (https://docs.microsoft.com/en-us/azure/virtual-machines/acu)
• NIC Private IP : 10.1.0.14
• Azure VM Networking, inbound port rules : Allow for any Port, any Protocol, any Source, any Destination
• Azure VM Networking, outbound port rules : Allow for any Port, any Protocol, any Source, any Destination
• System upgraded, updated etc. and then reboot
• Docker installed, "hello-world:latest" ok, reboot
• System upgraded, updated etc. and then reboot

Output of "docker version":

Client: Docker Engine - Community
 Version:           19.03.12
 API version:       1.40
 Go version:        go1.13.10
 Git commit:        48a66213fe
 Built:             Mon Jun 22 15:45:36 2020
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.12
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.13.10
  Git commit:       48a66213fe
  Built:            Mon Jun 22 15:44:07 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.2.13
  GitCommit:        7ad184331fa3e55e52b890ea95e65ba581ae3429
 runc:
  Version:          1.0.0-rc10
  GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683

Output of "docker info":

Client:
 Debug Mode: false

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 1
 Server Version: 19.03.12
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: false
 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: inactive
 Runtimes: runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 7ad184331fa3e55e52b890ea95e65ba581ae3429
 runc version: dc9208a3303feef5b3839f4323d9beb36df0a9dd
 init version: fec3683
 Security Options:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.3.0-1034-azure
 Operating System: Ubuntu 18.04.5 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 2
 Total Memory: 7.749GiB
 Name: test-l-001
 ID: 55PM:NZ2D:OVTG:4RIK:3TPN:ZP3B:NGZB:AGM6:XRSS:S2XX:AKQH:OTYT
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No swap limit support

---

That said:

1. VM Whiteouts in layers #2 (Ubuntu)
   Execute the following command:
   

    sudo docker swarm init --advertise-addr 10.1.0.14:2377
   

   This should be the result:

    Swarm initialized: current node ([REDACTED]) is now a manager.
   
    To add a worker to this swarm, run the following command:
   
    	docker swarm join --token [REDACTED] 10.1.0.14:2377
   
    To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.
   

2. VM Container tagging / naming #1 (Windows)
   Execute the following command:
   

    docker swarm join --token [REDACTED] 10.1.0.14:2377
   

   This should be the result:

    This node joined a swarm as a worker.
   

3. VM Whiteouts in layers #2 (Ubuntu)
   Execute the following command:
   

    sudo docker node ls
   

   This should be the result:

    ID             HOSTNAME            STATUS              AVAILABILITY        MANAGER STATUS      ENGINE VERSION
    [REDACTED] *   test-l-001          Ready               Active              Leader              19.03.12
    [REDACTED]     test-w-001          Ready               Active                                  19.03.5
   

4. VM Whiteouts in layers #2 (Ubuntu)
   Execute the following command:
   

    sudo docker pull curlimages/curl:latest
   

5. VM Container tagging / naming #1 (Windows)
   Execute the following command:
   

    docker pull mcr.microsoft.com/windows/servercore/iis
   

6. VM Whiteouts in layers #2 (Ubuntu)
   Create the following docker-compose, lets call it "docker-compose-test.yml":

    version: "3"
    services:
      curlc:
    	image: curlimages/curl:latest
    	command: tail -f /dev/null
    	deploy:
    	  mode: replicated
    	  replicas: 1
    	  placement:
    		constraints:
    		  - node.platform.os == linux
      iisc:
    	image: mcr.microsoft.com/windows/servercore/iis
    	deploy:
    	  mode: replicated
    	  replicas: 1
    	  placement:
    		constraints:
    		  - node.platform.os == windows
   

   ... and then launch it:

        docker stack deploy --compose-file docker-compose-test.yml test
   

   Check that the service is up:

    sudo docker container ls
   

   This should be the result:

    CONTAINER ID        IMAGE                    COMMAND                  CREATED             STATUS              PORTS               NAMES
    55dee8bf697b        curlimages/curl:latest   "/entrypoint.sh tail…"   22 seconds ago      Up 21 seconds                           test_curlc.1.wtd82bk3nysly017fvp56mghy
   

7. VM Container tagging / naming #1 (Windows) : check that the service is up : docker container ls

    CONTAINER ID        IMAGE                                             COMMAND                   CREATED             STATUS              PORTS               NAMES
    39c34be1aae7        mcr.microsoft.com/windows/servercore/iis:latest   "C:\\ServiceMonitor.e…"   2 minutes ago       Up 2 minutes                            test_iisc.1.lq7hio5vgvwhcfwn1ojd8xj0l
   

8. VM Whiteouts in layers #2 (Ubuntu)
   Execute the following command, keep in mind that the number of "a" is a very strict constraint:

    docker exec <curlc CONTAINER ID> curl -H "a:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" http://iisc
   

   This should be the result:

      % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
    								 Dload  Upload   Total   Spent    Left  Speed
    100   703  100   703    0     0   3739      0 --:--:-- --:--:-- --:--:--  3739
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
    <title>IIS Windows Server</title>
    <style type="text/css">
    <!--
    body {
    		color:#000000;
    		background-color:#0072C6;
    		margin:0;
    }
   
    #container {
    		margin-left:auto;
    		margin-right:auto;
    		text-align:center;
    		}
   
    a img {
    		border:none;
    }
   
    -->
    </style>
    </head>
    <body>
    <div id="container">
    <a href="http://go.microsoft.com/fwlink/?linkid=66138&amp;clcid=0x409"><img src="iisstart.png" alt="IIS" width="960" height="600" /></a>
    </div>
    </body>
    </html>
   

   That said, when adding a sufficient amount of characters to the header, the call hangs:

      % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
    								 Dload  Upload   Total   Spent    Left  Speed
      0     0    0     0    0     0      0      0 --:--:--  0:02:05 --:--:--     0
    curl: (56) Recv failure: Connection reset by peer
   

[thaJeztah]

The length of your header value is 1255 characters (1255*8=10040 bytes, assuming 8-bit).

Could this be a RequestLimit on the IIS server? https://docs.microsoft.com/en-us/iis/configuration/system.webserver/security/requestfiltering/requestlimits/ does the IIS-container receive the request? Anything in the logs for that container?

[riccaa]

The IIS values are the following:

{[maxAllowedContentLength, 30000000], [maxUrl, 4096], [maxQueryString, 2048]}

From the Windows machine I've used the command...

docker exec <curlc CONTAINER ID> curl -H "a:aaa[...]" http://iisc

... With many more "a", but all was fine, that is: IIS work as expected.

From Ubuntu, I execute the "usual" command with too many "a":

docker exec <curlc CONTAINER ID> curl -H "a:aaa[...]" http://iisc/

On Windows, using netstat, this is the result:

TCP    10.1.0.13:51416        [REDACTED]:http     ESTABLISHED

After a while (minutes, not seconds) the netstat's result is always the same.

[riccaa]

I have found the culprit and the workaround.

Culprit: mr. MTU

Workaround: see here and here.

That is...

1. VM #1 (Windows):
In C:\ProgramData\docker\config create the "daemon.json" file, if it is not present, and add "mtu": 1450.
If the file was empty the result should be something like this:

{
   "mtu": 1450
}

Restart the Docker service.

2. VM #2 (Ubuntu):
Change the "docker-compose-test.yml":

version: "3"

services:

  curlc:
    image: curlimages/curl:latest
    command: tail -f /dev/null
    deploy:
      mode: replicated
      replicas: 1
      placement:
        constraints:
          - node.platform.os == linux
    networks:
      test-network: null  
    
  iisc:
    image: mcr.microsoft.com/windows/servercore/iis
    deploy:
      mode: replicated
      replicas: 1
      placement:
        constraints:
          - node.platform.os == windows
    networks:
      test-network: null    

networks:
  test-network:
    driver: overlay
    driver_opts:
      com.docker.network.driver.mtu: 1400

Remove the old stack - if still present - and create a new one.

2. VM #2 (Ubuntu):
Execute the following comand:
sudo docker exec <curlc_CONTAINER_ID> curl -H "a:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa2aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" http://iisc
The header is three times bigger than the header used in the step nr. 8 but nonetheless the result is as expected:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>IIS Windows Server</title>
<style type="text/css">
<!--
body {
        color:#000000;
        background-color:#0072C6;
        margin:0;
}

#container {
        margin-left:auto;
        margin-right:auto;
        text-align:center;
        }

a img {
        border:none;
}

-->
</style>
</head>
<body>
<div id="container">
<a href="http://go.microsoft.com/fwlink/?linkid=66138&amp;clcid=0x409"><img src="iisstart.png" alt="IIS" width="960" height="600" /></a>
</div>
</body>
100   703  100   703    0     0   3429      0 --:--:-- --:--:-- --:--:--  3429

I've checked the issue using an hybrid swarm in...

• AWS
• Azure
• Google Cloud

... Without errors.