I plan to deploy a mini web app to resize photos to the heroku free tier. I read that the heroku file system is ephemeral - uploaded files get deleted when the dyno restarts. What I want to know is if I upload an image only for a short duration to change its properties and then download it, is there a chance that it will get deleted before I download it? That is, can the app get cycled when it is in use?
Regards,
Debashish
On a free tier a web dyno gets cycled on:
1) Dyno restarting - according to the documentation
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).
Restart can happen at any time then, when occurring, also in progress web request could be terminated. After the restart is triggered, you have 30 seconds to graceful shutdown before the process gets killed
2) Dyno sleeping - according to the documentation
If an app has a free web dyno, and that dyno receives no web traffic in a 30-minute period, it will sleep
If your web request executes during the same session all the operations to upload/change/download the image, you should be guaranteed the file does not get deleted in the process. However, you can avoid these events using monitoring services such as Pingdom or New Relic that can prevent a web dyno from sleeping
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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 deployed a to-do web service in heroku.
But I didn't know that saving file is only ephemeral.
It's still fine because my to-do is only for a day.
But I want it to be reset on 4 am to maintain the data for a day
Is there anyways to manually set dyno restarting time?
Or is there some free service which provides saving besides heroku?
It is not possible to schedule the restart time.
Using the Heroku CLI I guess you can script it (meaning your computer needs to be on all the times).
Be aware that a free Dyno goes to sleep after 30 min inactivity (no incoming traffic). Once asleep the first request will make it start again.
You should look at storing the file somewhere else (save it on Google docs or Amazon S3) so you don't lose your data if the Dyno restarts.
I have a website hosted on heroku. Whenever I load it for the first time after awhile (I haven't figured out the exact interval yet, be it days or hours), it takes upwards of 15 seconds to load. Subsequent loads are <1second, even if I clear the cache completely and open it in an incognito tab.
Why might this be? It almost seems like some kind of DNS issue but I haven't really got a clue. I don't know how to troubleshoot something like this. The situation seems to be the same even on other computers at other locations.
Quoting the Heroku docs:
If an app has a free web dyno, and that dyno receives no web traffic in a 30-minute period, it will sleep.
When the dyno receives traffic again, it will take a few seconds to wake up, hence the delay you've experienced.
Note that the Heroku free tier also has a maximum number of dyno hours per month. A sleeping dyno doesn't use any hours, but it does when it's active. When the hours are used up, the dyno won't wake up to incoming traffic.
You can see your remaining quota of dyno hours with:
$ heroku ps -a <app name>
Heroku suggests upgrading to a hobby dyno if your app needs to be permanently accessible. More info on https://devcenter.heroku.com/articles/free-dyno-hours
On the free tier, Heroku dynos go to sleep if they aren't used after an hour or something like that. They take a few seconds to wake up. Pay for the service and it stops happening, or write a script to ping your site every couple minutes or something.
Is it possible to stop a Heroku Daily Dyno Restart for a Hobby Dyno?
My Goal is to stop the Dyno from restarting.
In short, No (with an aside that the restart shouldn't be seen as a bad thing).
From the Heroku Dynos and Dyno Manager Docs
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).
Cycling happens for all dynos, including one-off dynos, so dynos will run for a maximum of 24 hours + 216 minutes.
In addition, dynos are restarted as needed for the overall health of the system and your app. For example, the dyno manager occasionally detects a fault in the underlying hardware and needs to move your dyno to a new physical location.
Additionally, Dynos Restart if you:
create a new release by deploying new code
change your config vars
change your add-ons
run heroku restart
With Hobby Dynos, the real issue is that inactivity causes the Dyno to sleep throughout the day. From my personal experience, waking up a sleeping dyno can cause a page to take ~30s to load.
There are many solutions to 'ping' the dyno on regular intervals to keep it 'awake'.
An example solution for a Node Server is heroku-self-ping
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.