envoyproxy/envoy

subset lb: support customized response code when using NO_FALLBACK

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#11,983 opened on Jul 9, 2020

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area/load balancingdesign proposalhelp wanted

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Description

We have a use case for the subset LB in which we'd like to return a 404 when there is no metadata/subset match. Right now, a 503 (no healthy hosts) response is the only possible response:

https://github.com/envoyproxy/envoy/blob/master/api/envoy/config/cluster/v3/cluster.proto#L206

We could make this knob something specific to the subset LB; or we could make it something generic for all LBs similar to ClusterNotFoundResponseCode (e.g.: EndpointNotFoundResponseCode):

https://github.com/envoyproxy/envoy/blob/master/api/envoy/config/route/v3/route_components.proto#L794

Thoughts?

cc: @zuercher @fishcakez @janephilipps @mattklein123

Contributor guide

Research direction
Examine the subset LB code and the ClusterNotFoundResponseCode pattern, then implement a customizable response code for no fallback.
Tech stack
cpp
Domain
backendapi
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++Protocol BuffersEnvoy development setup
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40