JupyterHub startup aborted by failure to connect to an external service (behavior change between jh 4.1.5 and 5.0.0-5.2.0)

[consideRatio]

In JupyterHub version 4.1.5, failures like not being able to connect to an external service hasn't led to exiting jupyterhub, but does so in jupyterhub 5.2.0.

I think this could be seen as a regression, but possibly also a fix. I lean to think its a regression and an unwanted change, because I think jupyterhub should expect to startup independently of an external service, otherwise for example, what if the external service depends on jupyterhub to be available to startup itself?

I've not tried what happens in jupyterhub 5.2.0 if we have an external service initially accessible during startup, which we then loose contact with - does that also lead to an error and stopping jupyterhub?

JupyterHub 5.0.0b1 - 5.2.0 behavior

[E 2024-10-18 10:18:09.522 JupyterHub app:3652] Cannot connect to external service binder at http://binderhub:8090. Is it running?
[D 2024-10-18 10:18:09.522 JupyterHub application:1060] Exiting application: jupyterhub

JupyterHub 4.1.5 behavior

kubectl logs -n staging hub-74b7569bcb-8td2w -c hub | grep binderhub 

[I 2024-10-04 07:37:39.514 JupyterHub app:3224] Adding external service binder at http://binderhub:8090
[E 2024-10-04 07:37:40.531 JupyterHub app:3246] Cannot connect to external service binder at http://binderhub:8090. Is it running?
[W 2024-10-04 07:38:41.631 JupyterHub app:2508] Cannot connect to external service binder at http://binderhub:8090
[W 2024-10-04 07:39:41.542 JupyterHub app:2508] Cannot connect to external service binder at http://binderhub:8090
[W 2024-10-04 07:40:41.450 JupyterHub app:2508] Cannot connect to external service binder at http://binderhub:8090
[W 2024-10-04 07:41:41.450 JupyterHub app:2508] Cannot connect to external service binder at http://binderhub:8090

[consideRatio]

The change comes from PR #4381, introduced in 5.0.0b1, specifically here: https://github.com/jupyterhub/jupyterhub/pull/4381/files#diff-24343a4facb880f2c9c882604e6b13654dccabee03f69097793fb2a79ce45ef2L3180-R3362

I think the situation is like this, where service.from_config and service.managed are considered:

from_config	managed	possible?	service issues -> jh startup aborted? (current)	... (in jh v4)
true	true	yes	yes	yes
true	false	yes	yes (a bug I think)	no
false	false	yes	no	-
false	true	no	-	-