Verify cluster creation options for dask_gateway works

[consideRatio]

In #2144 we have a basic example on how to use dask_gateway the client to create a dask cluster. But, the cluster creation options we are passed doesn't work. They are configured by us as 2i2c admins when setting up the dask-gateway the server via the dask-gateway helm chart here.

infrastructure/helm-charts/daskhub/values.yaml

Lines 154 to 214 in cf7bfc3

	optionHandler: |
	from dask_gateway_server.options import Options, Integer, Float, String, Mapping
	import string
	# Escape a string to be dns-safe in the same way that KubeSpawner does it.
	# Reference https://github.com/jupyterhub/kubespawner/blob/616f72c4aee26c3d2127c6af6086ec50d6cda383/kubespawner/spawner.py#L1828-L1835
	# Adapted from https://github.com/minrk/escapism to avoid installing the package
	# in the dask-gateway api pod which would have been problematic.
	def escape_string_label_safe(to_escape):
	safe_chars = set(string.ascii_lowercase + string.digits)
	escape_char = "-"
	chars = []
	for c in to_escape:
	if c in safe_chars:
	chars.append(c)
	else:
	# escape one character
	buf = []
	# UTF-8 uses 1 to 4 bytes per character, depending on the Unicode symbol
	# so we need to transform each byte to its hex value
	for byte in c.encode("utf8"):
	buf.append(escape_char)
	# %X is the hex value of the byte
	buf.append('%X' % byte)
	escaped_hex_char = "".join(buf)
	chars.append(escaped_hex_char)
	return u''.join(chars)
	def cluster_options(user):
	safe_username = escape_string_label_safe(user.name)
	def option_handler(options):
	if ":" not in options.image:
	raise ValueError("When specifying an image you must also provide a tag")
	extra_annotations = {
	"hub.jupyter.org/username": safe_username,
	"prometheus.io/scrape": "true",
	"prometheus.io/port": "8787",
	}
	extra_labels = {
	"hub.jupyter.org/username": safe_username,
	}
	return {
	"worker_cores_limit": options.worker_cores,
	"worker_cores": options.worker_cores,
	"worker_memory": "%fG" % options.worker_memory,
	"image": options.image,
	"scheduler_extra_pod_annotations": extra_annotations,
	"worker_extra_pod_annotations": extra_annotations,
	"scheduler_extra_pod_labels": extra_labels,
	"worker_extra_pod_labels": extra_labels,
	"environment": options.environment,
	}
	return Options(
	Integer("worker_cores", 2, min=1, label="Worker Cores"),
	Float("worker_memory", 4, min=1, label="Worker Memory (GiB)"),
	# The default image is set via DASK_GATEWAY__CLUSTER__OPTIONS__IMAGE env variable
	String("image", label="Image"),
	Mapping("environment", {}, label="Environment Variables"),
	handler=option_handler,
	)
	c.Backend.cluster_options = cluster_options

I assume we have a bug in these options, as I get this message.