Why does calling instance.exec with ready: true kill the whole container?

[ayushn21]

I've just been experimenting with async-container without any clear goals. I've got a basic project (attached) with a web executable that just logs to a file. It's meant to be a placeholder for a potential web server.

I start it in a container with instance.exec with ready: true. This instantly kills the container with the following logs:

  0.0s     info: Async::Container::Notify::Console [oid=0x258] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | {status: "Initializing controller..."}
  0.0s     info: WebController [oid=0x270] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Controller starting...
  0.0s     info: WebController [oid=0x270] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Starting container...
  0.0s    debug: Async::Container::Forked [oid=0x278] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Starting child...
               | {
               |   "child": {
               |     "key": null,
               |     "name": "Web",
               |     "restart": false,
               |     "health_check_timeout": null
               |   },
               |   "statistics": {
               |     "spawns": 1,
               |     "restarts": 0,
               |     "failures": 0,
               |     "restart_rate": 0.0,
               |     "failure_rate": 0.0
               |   }
               | }
  0.0s    debug: Async::Container::Forked [oid=0x278] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Started child.
               | {
               |   "child": {
               |     "name": "Web",
               |     "pid": 44682,
               |     "status": null
               |   },
               |   "spawn": {
               |     "key": null,
               |     "restart": false,
               |     "health_check_timeout": null
               |   },
               |   "statistics": {
               |     "spawns": 1,
               |     "restarts": 0,
               |     "failures": 0,
               |     "restart_rate": 0.0,
               |     "failure_rate": 0.0
               |   }
               | }
  0.0s     info: WebController [oid=0x270] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Waiting for startup...
  0.0s    debug: Async::Container::Forked [oid=0x278] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Waiting for ready:
               | 	#<Async::Container::Forked::Child name="Web" status=nil pid=44682>: {}
  0.0s    debug: Async::Container::Group [oid=0x298] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Waiting for children...
               | {
               |   "duration": null,
               |   "running": {
               |     "#<IO:0x000000011c796ea0>": "#<Fiber:0x000000011c79af00 /Users/ayush/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/async-container-0.34.4/lib/async/container/generic.rb:217 (suspended)>"
               |   }
               | }
  0.0s    debug: Async::Container::Forked [oid=0x278] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | All ready:
               | 	#<Async::Container::Forked::Child name="Web" status=nil pid=44682>: {ready: true, status: "(exec)"}
  0.0s     info: WebController [oid=0x270] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Finished startup.
  0.0s     info: Async::Container::Notify::Console [oid=0x258] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | {ready: true, size: 1, status: "Running with 1 children."}
  0.0s     info: WebController [oid=0x270] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Controller started.
  0.0s    debug: Async::Container::Group [oid=0x298] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Waiting for children...
               | {
               |   "duration": 0.9999979995191097,
               |   "running": {
               |     "#<IO:0x000000011c796ea0>": "#<Fiber:0x000000011c79af00 /Users/ayush/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/async-container-0.34.4/lib/async/container/generic.rb:217 (suspended)>"
               |   }
               | }
  0.0s    debug: Async::Container::Forked::Child [oid=0x288] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Waiting for process to exit...
               | {
               |   "child": {
               |     "process_id": 44682
               |   },
               |   "timeout": 0.1
               | }
 0.11s     warn: Async::Container::Forked::Child [oid=0x288] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Process is blocking, sending kill signal...
               | {
               |   "child": {
               |     "process_id": 44682
               |   },
               |   "timeout": 0.1
               | }
 0.11s    debug: Async::Container::Forked::Child [oid=0x288] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Process exited.
               | {
               |   "child": {
               |     "process_id": 44682,
               |     "status": "pid 44682 SIGKILL (signal 9)"
               |   }
               | }
 0.11s    error: Async::Container::Forked [oid=0x278] [ec=0x280] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Child exited with error!
               | {
               |   "status": "pid 44682 SIGKILL (signal 9)",
               |   "stopping": false
               | }
 0.11s     info: Async::Container::Forked [oid=0x278] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Stopping container...
               | {
               |   "timeout": false
               | }
 0.11s    debug: Async::Container::Group [oid=0x298] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Stopping all processes...
               | {
               |   "graceful": false
               | }
 0.11s     info: Async::Container::Forked [oid=0x278] [ec=0x260] [pid=44665] [2026-04-06 21:22:10 +0100]
               | Group has stopped.

Why does this happen when ready is set to true but not false?

Here's my project: async-container-ready.zip

To reproduce:

$ cd async-container-ready
$ bundle install
$ bundle exec start

[ioquatix]

Thanks for your report, I will take a look.

[ioquatix]

We may need this fix: #55

[ayushn21]

Yep that seems to have fixed it, thanks!! I did try to look into the code yesterday but tied myself into knots!

After your fix, this line is logged at regular intervals:

| Waiting for children...
| {
|   "duration": 9.999797999858856,
|   "running": {
|     "#<IO:0x000000011fe631b8>": "#<Fiber:0x000000011fe66b38 /Users/ayush/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/bundler/gems/async-container-0a71bb9d9bd7/lib/async/container/generic.rb:217 (suspended)>"
|   }
| }

This happens when setting ready: true or setting ready: false and manually sending the ready! notification. Based on my understanding of the code, this comes from group.rb:

# Begin any outstanding queued processes and wait for them indefinitely.
def wait
  with_health_checks do |duration|
    self.wait_for_children(duration)
  end
end

As such it means that the container is healthy and running? Is that interpretation correct?

[ioquatix]

Yes, that's the internal health check.

[ayushn21]

Thanks! Might be worth improving the log message there? It confused me for a bit thinking it was waiting and checking for the children to be ready. I'll have a poke around and make a PR when I get some time.

[ioquatix]

Yep, I'd be okay with a PR to improve the log message - I think it's an internal debug message.