All-zero weights: is it allowed and how is traffic distributed

[linki]

There is unclarity how an all-zero traffic weight is handled and interpreted.

Handled (currently):

• rejected by at least one client (zkubectl)
• Not handled by the server (stackset controller allows this setting)

Interpretation (currently)

• stackset-controller resolves all-zero weights to equal traffic distribution
  • this seems undesireable by a majority of users at the moment

Clarify what's the desired behaviour:

• Should all-zero weights be possible at all
  • where to make the validation and reject the request?
• How to interpret all-zero weights if allowed
  • equal distribution or zero traffic

[szuecs]

What does reject the request mean?
Maybe 404?
What if we have routes / and /api and traffic to /api will be set to 0 for all. The http routing tree will probably delete the route and will send the traffic to the routes for /, which might not be what the user thought "all 0" means.

The longer I think about this case the more I think we should disallow this setting.