SkyServe: warn/raise on min_replicas: 0

[concretevitamin]

Tried the http server example with min_replicas: 0 and got

Services
NAME  UPTIME  STATUS        REPLICAS  ENDPOINT
http  -       REPLICA_INIT  0/0       172.190.62.140:30001

Service Replicas
No existing replicas.

At this point there's no way to curl and trigger a scale-up.

We should consider raising a ValueError / NotImplementedError about this.

cc @MaoZiming @cblmemo

[cblmemo]

Humm, did you specify max_replicas=<some positive integer>? If not, the default value of max_replicas is min_replicas, and no autoscaling is enabled. I think if you specify min_replicas=0, max_replicas=1 and curl the endpoint, then it will trigger a scale-up.

[MaoZiming]

@cblmemo I think we need special handling for min_replicas=0, I believe currently it will take multiple curl's + some delay to trigger a scale-up when num replicas is 0.
User might prefer immediate scale-up when there is request.
It also shows REPLICA_INIT when there is no replica with no scale-up.

[concretevitamin]

+1. I believe I set min_replicas: 0 and max_replicas: 1.

[cblmemo]

Sounds great! Lets keep min_replicas>0 for now