envoyproxy/envoy

Do not close health check connections when draining

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#20,748 opened on Apr 8, 2022

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area/health_checkinghelp wanted

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Description

Description: When Envoy is draining (via /healthcheck/fail) the HttpConnectionManager will send a GOAWAY or Connection:close on both application and health check connections – even if the health check requests are setting Connection: keep-alive.

In an active health checking setup, this causes unnecessary connection churn for health check connections – clients will continue to send health check requests, but will need to open a new connection each time.

This is problematic for servers that (a) receive a lot of health checks (b) use mTLS even for health check requests.

I would expect that if the health check filter is configured, Envoy would keep these connections alive.

Repro steps:

  • Configure Envoy as below
  • Drain Envoy with healthcheck/fail
  • Send HTTP/1 health check request with Connection: keep-alive
  • Observe 503 response with Connection: close header

Config:

  • HttpConnectionManager
  • HTTP Health Check filter

If this behaviour seems reasonable to folks, would love to hear how to approach adding this to Envoy.

Contributor guide

Research direction
Examine the HttpConnectionManager's drain logic in source/common/http/conn manager impl.cc. Identify where GOAWAY or Connection:close are sent to health check connections. Modify the logic to skip sending those on health check connections by checking if the connection is used for health checks (e.g., via the health check filter or a flag). Ensure health check connections remain alive during draining.
Tech stack
cpp
Domain
backendinfrastructure
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
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++HTTPnetworking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40