Magento2: Queue consumers

[luckyraul]

Preconditions (*)

Then you deploy a next release you still have queue consumers running from the old releases. And where is no way to stop them

Steps to reproduce (*)

run cron on the first release
release new version
run cron on the second release
release new version
run cron on the third release

Expected result (*)

only new process running

releases/745/bin/magento queue:consumers:start product_action_attribute.website.update

Actual result (*)

still running old processes

releases/743/bin/magento queue:consumers:start product_action_attribute.website.update
releases/744/bin/magento queue:consumers:start product_action_attribute.website.update
releases/745/bin/magento queue:consumers:start product_action_attribute.website.update

[m2-assistant[bot]]

Hi @luckyraul. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• [ ] Summary of the issue
• [ ] Information on your environment
• [ ] Steps to reproduce
• [ ] Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

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For more details, please, review the Magento Contributor Assistant documentation.

@luckyraul do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• [x] yes
• [ ] no

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[engcom-Charlie]

Hello @luckyraul ! Can you provide more steps how to reproduce it ?

[luckyraul]

I don't do anything except running cron before and after release. Updated issue description

[slackerzz]

You need to share the var directory between releases

[luckyraul]

you cannot share var

[slackerzz]

@luckyraul why not? I'm using capistrano with https://github.com/davidalger/capistrano-magento2 to deploy and i assure you that you can:

[hostep]

@slackerzz: it's not really recommended to share the full var directory in between releases. Especially if you use file based caching for example. You want the cache to not be shared in between releases.

The examples in the repo's README you reference also shares only specific individual files or directories within the var directory:

set :linked_files, [
  'app/etc/env.php',
  'app/etc/config.local.php',
  'var/.setup_cronjob_status',
  'var/.update_cronjob_status'
]

set :linked_dirs, [
  'pub/media',
  'pub/sitemaps',
  'var/backups', 
  'var/composer_home', 
  'var/importexport', 
  'var/import_history', 
  'var/log',
  'var/session', 
  'var/tmp'
]

Can you tell us a bit more about those .pid files in the var directory btw, how do those work exactly? (I'm assuming you reference to those in your statement about sharing the var directory?)

I'm also running against the problem of @luckyraul with our capistrano-style deployments and I'm wondering if those .pid files can help resolve that or not, but I don't fully understand how they work yet?

Thanks!

[slackerzz]

Hi @hostep, you're right, it's not ideal but i'm not using files for caching, i use Redis.
However I created a systemd service to run my consumer because at the time of Magento 2.1 there wasn't an option to run it by cron.

When the consumer is started for the first time it creates a pid file in the magento var directory.
Every subsequent cron execution checks for the pid file, if this exists the consumer is not started again. Take a look at https://github.com/magento/magento2/blob/2.3-develop/app/code/Magento/MessageQueue/Model/Cron/ConsumersRunner.php

When you deploy a new release and with a non shared var directory the pid file is not there and so magento creates another process.

Maybe it could be better to create a var/pid directory and share only this between releases.

Another solution can be to stop consumers before deploying a new release. For example on Magento Cloud Commerce all cron processes are killed during a deploy.

[luckyraul]

@slackerzz
Firstly there is no command to stop them.
Secondly it is not a var/pid.
Lastly, If we keep pid files shared it will not start a new one if there is old running? Am I correct? This creates a new problem because old code will be still running

[hostep]

Out of curiosity: is it safe to kill these queue:consumers:start processes? What if some message is just being handled by that process and in the middle of it you kill that process, what happens then? (sorry for asking stupid questions, I don't quite understand yet how the whole message queueing works in Magento and how stable it is).

Also: what we are seeing, is that no new queue:consumers:start processes get started up, even if the PID files are gone and when the old queue:consumers:start processes are still running while pointing to a release which no longer exists and also pointing to PID files which no longer exists. These processes are then still using code from the old release loaded in memory I guess.
Update: this statement doesn't seem to be correct, still trying to figure it out, but weird things happen after deploys on our server.

I also noticed Magento came with something called a poison pill feature in Magento 2.3.2, but I don't know if that is relevant here and if we can use that somehow to tell the queues to stop and restart from a new release?

[slackerzz]

@luckyraul

Firstly there is no command to stop them.

kill will do the work

Secondly it is not a var/pid.

I was suggesting that we can think to submit a pull request to change the pid file location to var/pid to not share all the var directory between release. I know that there is no var/pid directory.

Lastly, If we keep pid files shared it will not start a new one if there is old running? Am I correct? This creates a new problem because old code will be still running

You're right

@hostep i didn't know about the PoisonPill, maybe this can resolve the last point of @luckyraul

My "personal" solution was to add

'cron_consumers_runner' => [
        'cron_run' => false
    ]

to app/etc/env.php to disable automatic consumer start by cron.
Then I create a systemd service to manage my consumer. In this way i can service myconsumer start, service myconsumer restart etc

[arnoudhgz]

I can also easily reproduce it by just manually creating an export job with a lot of products. After that all other cron tasks get status missed (payments, indexers etc).

So this is not only happening when doing a new release.

Small exports are fine though....

[alaa-almaliki]

I just came across the issue today and seen tasks from old releases keep running in memory. This has caused a memory issue and dev server has went irresponsive. Killed all the queue tasks and disabled them to avoid memory issue.

'cron_consumers_runner' => [
        'cron_run' => false,
        'max_messages' => 20000,
        'consumers' => [],
 ],

The memory is reclaimed now and no more issues post deployments.

[hostep]

Be aware that certain tasks being executed in the backend will no longer work when you disable all the consumers. These are the things listed under Merchant tool enhancements in the 2.3.2 release notes.

Anyway, I've created a feature request for an easy-to-use action to stop running consumer processes. We could then use this during a deployment. If somebody has some ideas, feel free to contribute: https://github.com/magento/community-features/issues/181

Until this feature is implemented, I'm currently solving it by reading the var/*.pid files from the previous release, and killing all those pid's using the kill command. Not sure how safe it is to do it like that, but that resolved our deployment problems for now.

[giacmir]

There are two problems with the current PoisonPill implementation:

1. the current poisonpill version is invalidated only when config is saved or a new website/store/store-view is added,it could happen that a new deploy doesn't trigger one of these two events.
2. the consumer check for the poisonpill only when it receives a message, so if your messages aren't very frequent (let say in a test environment) you may have several old consumers waiting for the message that will kill them. All those strand processes can easily saturate a test machine.

[hostep]

@giacmir indeed!

See https://github.com/magento/architecture/pull/232/files?short_path=81c5aa0#diff-81c5aa0b55a519b20c0ffd8b3f57b21b for a proposal for some new functionality in Magento for how to handle those. Especially "Problem 2" is relevant here.

[Zyles]

Same problem. Our server died because old consumers were running and spiked CPU load after we moved to a new release.

Is consumers supposed to be running 24/7? "ps aux | grep consumers" have 4 consumers running at all times.

[hostep]

@Zyles: yes, that's how it was designed, if you don't need the functionality provided by those consumers, you can disable all or some of them, see docs.

Magento 2.3.4 came with a new option consumers-wait-for-messages, which will kill the consumer process just after it got started up and noticed no messages were in the queue. This means that every minute a new process starts up, takes a lot of memory, looks for pending message, if any found processes them, and then kills itself. This feels like too much overhead to me.

Therefore I proposed a different idea for doing the check on pending messages before the processes start up, see here, option only-spawn-when-message-available. Work on this hasn't started as far as I'm aware, but I'm not in the loop, so maybe it has started already, who knows ... :)

[amenk]

Then I create a systemd service to manage my consumer. In this way i can service myconsumer > start, service myconsumer restart etc

The solution by @slackerzz sounds very reasonable to me. Those systemd services should be in the devdocs :)

Starting the consumers via cron also seems to have the side-effect, that the first cron-run never returns