Support for Dask Gateway clusters from config

Right now, IIUC, to create a cluster using the button the config takes a python class, args, and kwargs to create the cluster. This isn’t flexible enough for dask-gateway, which requires creating an intermediate Gateway object.

Two options

1. Expand the logic of the lab extension’s cluster creation to take a snippet of code to run.
2. Update dask-gateway to have a “simple” way of creating a cluster that just uses the defaults (cc @jcrist).

https://github.com/dask/dask-gateway/issues/55 is related, but more focused on expanding dask-labextension to take advantage of dask-gateway

[jcrist]

dask-gateway doesn’t require creating an intermediate Gateway object - you can already call dask_gateway.GatewayCluster directly (we might want to update our docs to better show this). I’ve verified things work with dask-labextension with default parameters just like any other cluster.

[thomafred]

I see that @consideRatio found a fix using the GatewayCluster-class (https://github.com/dask/dask-labextension/issues/203). Confirmed to work with the daskhub helm-chart:

jupyterhub:
  hub:
    extraConfig:
      10-patch-dask-labextension-config: |-
        c.KubeSpawner.environment.setdefault("DASK_LABEXTENSION__FACTORY__MODULE", "dask_gateway")
        c.KubeSpawner.environment.setdefault("DASK_LABEXTENSION__FACTORY__CLASS", "GatewayCluster")
        c.KubeSpawner.environment.setdefault("DASK_LABEXTENSION__FACTORY__ARGS", "[]")
        c.KubeSpawner.environment.setdefault("DASK_LABEXTENSION__FACTORY__KWARGS", "{}")

However, the DASK DASHBOARD URL is not set correctly as mentioned by Erik in the issue above.