title: "404 Not found" when trying to connect to dask dashboard
body: <p>I'm using dask.distributed on a remote machine accessible via SSH, and attempting to connect to the Dask dashboard. I remember it's worked before (in other virtual environments) when I was doing my first steps with Dask, but now any time I try to connect to <a href="http://localhost:8787/" rel="nofollow noreferrer">http://localhost:8787/</a> or <a href="http://localhost:8787/status" rel="nofollow noreferrer">http://localhost:8787/status</a> I get a "404 Not found" error. </p>
  
  <p>Since the machine is only accessible via SSH I've set up an SSH tunnel to be able to access the dashboard using a browser from my desktop, and that gives me that 404 -- so somehow the server is working and accepting connections but not serving the pages. Also, connecting to it locally on the command line using lynx or telnet yields the same error. I'm also sure that nothing else is running on port 8787.</p>
  
  <p>Are additional packages required for the dashboard to work? Here's my environment: </p>
  
  <pre><code>$ pip freeze
  click==7.1.2
  cloudpickle==1.4.1
  dask==2.18.1
  distributed==2.18.0
  HeapDict==1.0.1
  msgpack==1.0.0
  numpy==1.18.5
  psutil==5.7.0
  PyYAML==5.3.1
  sortedcontainers==2.2.2
  tblib==1.6.0
  toolz==0.10.0
  tornado==6.0.4
  zict==2.0.0
  $ python
  Python 3.7.5 (default, Nov 12 2019, 11:34:05)
  [GCC 4.4.7 20120313 (Red Hat 4.4.7-18)] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; from dask.distributed import Client
  &gt;&gt;&gt; client = Client()
  &gt;&gt;&gt; client
  &lt;Client: 'tcp://127.0.0.1:40076' processes=4 threads=16, memory=135.43 GB&gt;
  &gt;&gt;&gt; client.scheduler_info()
  {
    'type': 'Scheduler', 
    'id': 'Scheduler-1662a23e-a12b-4640-832e-75c5c45c83b0', 
    'address': 'tcp://127.0.0.1:40076', 
    'services': {
      'dashboard': 8787
    }, 
    'workers': {
      'tcp://127.0.0.1:34228': {
        'type': 'Worker', 
        'id': 1, 
        'host': '127.0.0.1', 
        'resources': {}, 
  ...
  </code></pre>
  
  <p>From another console: </p>
  
  <pre><code>$ telnet 127.0.0.1 8787
  Trying 127.0.0.1...
  Connected to 127.0.0.1.
  Escape character is '^]'.
  GET / HTTP/1.0
  
  HTTP/1.1 404 Not Found
  Server: TornadoServer/6.0.4
  Content-Type: text/html; charset=UTF-8
  Date: Mon, 15 Jun 2020 17:34:37 GMT
  Content-Length: 69
  
  &lt;html&gt;&lt;title&gt;404: Not Found&lt;/title&gt;&lt;body&gt;404: Not Found&lt;/body&gt;&lt;/html&gt;Connection closed by foreign host.
  $
  </code></pre>