openresty/lua-nginx-module

ngx.pipe.spawn shell mode child process not killed after openresty exits

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#1,855 opened on Feb 19, 2021

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good first issue

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Description

When using ngx.pipe.spawn in shell mode (args is a string), sh -c in invoked internally. While OpenResty exists, SIGKILL is sent to sh process, but it's not able to propogate to child process. The child process is then left alive.

POC:

init_work_by_lua_block {
  require("ngx.pipe").spawn("/tmp/a.py")
}

$ cat /tmp/a.py:

#!/usr/bin/env python3
import time
time.sleep(23333)

Then signal stop the OpenResty/Nginx process.

Contributor guide

Research direction
Examine the implementation of ngx.pipe.spawn in shell mode within the lua nginx module, specifically in `ngx pipe.c` or similar files. Identify how the child process is spawned via `sh c` and how OpenResty's shutdown sends SIGKILL. Investigate whether using process groups (e.g., `setsid`) or signal forwarding could propagate the kill to the grandchild. Look at existing comments or linked discussions for partial solutions. Test a fix by modifying the spawn logic to create a process group and kill the group on shutdown.
Tech stack
cshell
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Unix process signalsOpenResty internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25