I have an app which requires long running processes - typically over 2 hours (recording streaming media). Based on Heroku's website, my worker server running these processes will be restarted randomly, at least once per day.
Is there anyway to control/avoid these restarts, so as not to interrupt my long running processes?
Do other paas providers avoid this issue?
I don't know, How to control/avoid these restarts. I was also going through their documentation, They clearly state that "Dynos are also cycled at least once per day, in addition to being restarted as needed for the overall health of the system and your app."
I think, Dynos restart should only take placed when system behaves unexpected or Dynos are found in crashed state OR In month or week to clear cache memories.
You can try App42 PaaS which monitors your Apps continuously to make sure that they are up and running. If any kontena is found in crashed state, Health Monitor try to bring it back to working state. if unable than that particular kontena is deleted & replaced with a new one.
Disclaimer: I work for App42 PaaS.
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I have an application that is hosted on Heroku. The application has a process that is run on the server, that the user has the ability to start and stop. Once the user clicks 'Start', the process is supposed to stay running until the user presses 'Stop'. The functionality of the app should allow that the process can be run for extended periods of times (6 months or so) continuously.
I have deployed my app on a Heroku free dyno. While reading the Heroku documentation, I came across this page that states that Heroku Dynos are restarted automatically every 24 hours. Here is the relevant passage:
Dynos are also restarted (cycled) at least once per day to help maintain the health of applications running on Heroku. Any changes to the local filesystem will be deleted. The cycling happens once every 24 hours (plus up to 216 random minutes, to prevent every dyno for an application from restarting at the same time). Manual restarts (heroku ps:restart) and releases (deploys or changing config vars) will reset this 24 hour period. Cycling happens for all dynos, including one-off dynos, so dynos will run for a maximum of 24 hours + 216 minutes. If you have multiple dynos, they should cycle at different times based on the random 0 to 216 minutes difference. If you continually make changes to your application without a 24 hour gap, you won’t see cycling at all.
Does this mean that the user process that he/she has started will automatically be stopped when the dyno restarts? If yes, does it automatically resume the user process where it left off?
If not, I will have to find a different hosting solution since the process may need to be run 24x7x365.
Does this mean that the user process that he/she has started will automatically be stopped when the dyno restarts?
Yes it does. As it will when you change config variables, or deploy updates, or add / remove addons.
If yes, does it automatically resume the user process where it left off?
No it doesn't. Any safe-and-resume behaviour you have to implement in your application. When stopping processes, Heroku will send them a SIGTERM signal and give them 30 seconds to safe their work.
If not, I will have to find a different hosting solution since the process may need to be run 24x7x365.
I doubt that there is any hosting solution that will give you what you want. In a cloud environment restarts are a thing that happens all the time, at least for you updating your application, bugfixes, security fixes. Every hosting provider or platform that provides you with 24x7x365 uptime will also restart and replace your dynos all the time.
I have a Hobby Dyno that hosts an application in Heroku in which users can upload images.
What I've noticed is the Dyno restarts during his cycle causing all images to be gone.
2018-07-27T16:23:09.914767+00:00 heroku[web.1]: Cycling
2018-07-27T16:23:09.915421+00:00 heroku[web.1]: State changed from up to starting
I am aware of solutions that involve a third-party storage or host the app in another platform altogheter.
I am wondering if there is a way to stop a dyno cycle and never make it restart such as is always in the up state?
Thank you.
There is no way to prevent dyno cycling. Heroku does this automatically at least once per day.
Heroku's entire design is based on The 12-Factor App, which states that your app's processes are disposable. Heroku accomplishes this (in part) with its ephemeral file system, which is why you must persist files using an external service.
I'm testing an app with a worker and a web dyno on Heroku free tier and I'd like to keep the worker alive to be able to execute background tasks while letting the web dyno idle. By default they both go idle in 30 mins even if I have things queued on the worker.
I understand there're ways to keep the web dyno alive (and with that the worker as well), and there're ways to keep the web alive while scaling down the worker. However I'd need the worker alive and the web in idle.
I tried running a recurring job on the worker which would
Restart the dyno.
Scale the dyno down and then back up.
Both approaches worked (as in they restarted and scaled the dyno correctly) but the worker dyno would still idle after 30 mins (as if it's dependent on the web dyno). Edit: yep, that's pretty much the case as explained here: https://devcenter.heroku.com/articles/free-dyno-hours#dyno-sleeping
I could do this form the outside but it seems I'd have to constantly check for the state since a new restart doesn't seem to give me 30 mins headway. I'd also have to expose the API key which I'd like to avoid.
If I've gotten you right, you're trying to stop the web dyno and leave the worker dyno alive.
You could do that by going to the Resources tab:
And then in the 'web' section:
Press the pencil, toggle it off and press 'Confirm'.
As a workaround I currently remove the web dyno and explicitly enable it when I need it. As explained here:
Worker-only Free dynos do not sleep since they do not respond to web
requests.
My workaround was to just create two apps that deploy automatically from the same repository. Then, all you would need to do is enable the worker dyno for one and the web dyno for the other.
I am new to Go and I am using go routines in my app in Heroku, which are long (up to 7 minutes), and cannot be interrupted.
I saw that the auto scaler sometimes kills the Heroku dyno which is running the routine. I need a way of running this routine independently from the dynos so I know that it will not get shutdown. I read articles and still don't understand how to perform a go routine in a background worker. It is hard for me to believe I am the only one experiencing this.
My go routines use my redis database.
Could someone please point me to an example of how to setup a background worker in heroku for go and how to send my go routine to that worker?
Thank you very much
I need a way of running this routine independently from the dynos so I
know that it will not get shutdown.
If you don't want to run your worker code on a dyno then you'll need to use a different provider from Heroku, like Amazon AWS, Digital Ocean, Linode etc.
Having said that, you should design your workers, especially those that are mission critical, to be able to recover from a shutdown. Either to be able to continue where they left off or to start over. Heroku's dyno manager restarts the dynos at least once a day but I wouldn't be surprised if the other cloud providers also restart their virtual instances once in a while, probably not once a day but still... And even if you decide to deploy your workers on a physical machine that you control and never turn off, you cannot prevent things like hardware failure or power outage from happening.
If your workers need to perform some task till it's done you need to make them be aware of possible shutdowns and have them handle such scenarios gracefully. Do not ever rely on a machine, physical or virtual, to keep running while your worker is doing it's job.
For example if you're on Heroku, use a worker dyno and make your worker listen for the SIGTERM signal, after your worker receives such a signal...
The application processes have 30 seconds to shut down cleanly
(ideally, they will do so more quickly than that). During this time
they should stop accepting new requests or jobs and attempt to finish
their current requests, or put jobs back on the queue for other worker
processes to handle. If any processes remain after that time period,
the dyno manager will terminate them forcefully with SIGKILL.
... continue reading here.
But keep in mind, as I mentioned earlier, if there is an outage and Heroku goes down, which is something that happens from time to time, your worker won't even have those 30 seconds to clean up.
I have a Heroku worker setup to do a long running job which iterates over long periods. However whenever I do an update & deploy of other files in the repo this worker restarts, which is annoying, any way to avoid this?
No. This behaviour is part of Heroku's Automatic Dyno Restarting.
You can't work around this. Instead, you need to build all parts of your app to be able to function properly despite the fact that all dynos will restart at least once every 24 hours or so, whether or not you deploy updates in your repo.
Most significantly, you need to build support for Graceful Shutdown into all your processes (e.g. web process and worker processes).