Access dashboard from scheduler with no public IP?

Is it possible to connect to a scheduler without a public IP running in the same AWS VPC?

**What happened**:

I'm running a jupyter lab on an AWS EC2 instance and I'm trying to connect to a scheduler with a private IP that was created with `dask-cloudprovider` running in the same VPC as the lab.

The dashboard gets picked up by the extension as expected, all buttons become orange:


But if I open any of them, they remain blank for a while until they error out with a "took too long to respond" message:



**What you expected to happen**:

The extension showing the requested plots and metrics.

**Anything else we need to know?**:

Accessing the dashboard from the lab terminal with curl works, showing that it's not a basic networking issue:


Nothing apparent in the console:


Extensions:

```
jovyan@201435007e31:~$ jupyter serverextension list
config dir: /usr/local/etc/jupyter
dask_labextension enabled
- Validating...
dask_labextension 5.0.1 OK
jupyter_server_proxy enabled
- Validating...
jupyter_server_proxy OK
jupyterlab enabled
- Validating...
jupyterlab 3.0.16 OK
```

**Environment**:

- Dask version: 2021.5.0
- Python version: 3.8.8
- Operating System: Ubuntu Bionic
- Install method (conda, pip, source): pip