If I have an app on Heroku that consists of one worker and one or no web dynos, will it run? I'm unsure if the absent or idling web dynos will cause the worker dyno not to run.
Heroku doesn't just run web dynos, in fact, it makes no assumptions at all with regards to the processes you're running. There's absolutely nothing wrong with launching a single worker process.
This is actually a common scenario for me to deploy single cron-like tasks to Heroku, I've written about it here http://blog.y3xz.com/blog/2012/11/16/deploying-periodical-tasks-on-heroku/
If you are looking for cron-like tasks for simple jobs (like I am), now you have another alternative: Heroku Scheduler. It is easy to configure in a dashboard.
Advantage:
No need to choose and learn a new scheduler library. Configure it in seconds.
Same way for different platforms: Python, Ruby, etc.
Save Dyno Hours for Free Plan user. Only the actual working time counts. Some scheduler library (like Rufus Scheduler) will keep running between launches (so that it does not rely on cron to work).
Disadvantage:
Trivial options. You can only choose among "Daily"/"Hourly"/"Every 10 minutes".
Conclusion: Best for basic use.
Related
I am currently using a Hobby dyno to run my web process -- frontend website as well as an API. To execute jobs, I need to run a background process that processes these jobs. Do I need to spin up another dyno that specifically runs background workers? I ask this because I see that Standard 1X/2x dynos include "unlimited background workers" which makes me think that multiple process types can run on a single dyno. It looks like I can run 2 hobby dynos -- one for web, one for workers or upgrade to one of the standard dynos...is this correct?
I believe that yes, if you want to have a dedicated worker app, that needs to be a separate dyno. You can run the processes in memory though and that saves you doing it with a separate binary/dyno
I'm a little bit confused about the whole dyno business with heroku . On their site, they define a dyno as:
A dyno is a lightweight Linux container that runs a single
user-specified command. A dyno can run any command available in its
default environment (what we supply in the Cedar stack) or in your
app’s slug (a compressed and pre-packaged copy of your application and
its dependencies).
This (somewhat?) makes sense in my head, but when I think about dynos in the context of multiple dynos running for one web app, my brain gets twisted.
Lets I'm building a web app with a server which runs a very important task only once every 3 hours for all users. If I am running multiple web dynos for this site, does that mean there is a separate server instance running on each dyno? And would that very-important-task that is run every 3 hours be run on each dyno every 3 hours?
Thanks a lot for any clarification!
Each dyno is an LXC container running in one of the heroku instances.
Depending of your dyno size, there might be other containers on the same instance or not.
But the rough idea is that yes, each dyno you have running is a different instance, and a task set to run on any web dyno each 3 hours will run on all of them.
You may want to look into the heroku scheduler addon. It will run a one-off dyno at a specified interval, allowing you to run cron-like tasks.
Very similar question to Is it feasible to run multiple processeses on a Heroku dyno?, or Running Heroku background tasks with only 1 web dyno and 0 worker dynos except I'm talking about a Ruby on Rails app.
Context:
I understand that it's encouraged to separate worker and web dynos... but I'm still testing and don't want to pay the expense. Especially because with my app, all the web requests pretty much happen either in the AM or in the PM, and during the whole middle of the day (and also middle of the night), literally nothing is happening.
I'd like the web dyno to run two types of background processing on the "downtime":
A recurring, long-running task every day (mailings)
An asynchronous, long-running task that is triggered when a user performs a certain action (it's a mailer)
I've done quite a bit of reading on this, but this is my first time doing anything asynchronous, so I wanted to ask the community a couple of questions just to ensure what I'm trying to do is feasible.
Questions
How do I do activity #1 for free?
To put it bluntly... considering my context above, if I use Heroku's Scheduler add-on, this runs a one-off dyno which I'll be charged for since I use NewRelic now to constantly ping my web dyno so it never actually sleeps meaning my one web dyno is my free dyno. Is there another way of doing this with the one web dyno that, in the middle of the night, won't be processing any requests? Alternatively, is there a way to tell New Relic to ping except at certain times, which will also then allow me to spin up a one-off dyno but still be within my free dyno hours?
For activity #2, I'm thinking of using Delayed Jobs, but how do I tell Delayed Jobs to delay until end of user 1's session, and then run mailer for user 1, but then pause again if user 2 sends a request, and then when user 2 is finished, start where left off on user 1's mailer, and then do user 2's mailer... and so forth? I think the root of the challenge here is that from what I've read, Delayed Jobs needs to be started with a script. But I'm not going to be at my computer starting a script all the time. How do I make the start (and the queue as illustrated in the question) something that happens automatically?
Would love even just point me directional pointers on what methods/ what considerations, etc.
I'm going to check out a nifty gem https://github.com/brandonhilkert/sucker_punch to do this. According to the author, it was written specifically to use Heroku's single dyno for hobby websites that have no need to spin up another dyno. It basically creates another thread.
FYI also, there is an add-on link that allows sucker_punch to do recurring tasks, called https://github.com/facto/fist_of_fury
My understanding is that Heroku charges Cron tasks based on the actual amount of time the task runs, using a dyno (based on: https://devcenter.heroku.com/articles/scheduler#dynohour-costs).
So, if I need a quick task to run every X minutes, I could use the cron addon to process it, instead of a worker dyno and I would be charged a fraction of the cost.
So, if everything above is true, what is the use of the Iron.io workers? They charge (about) the same as dynos from the cron jobs and they can't connect to the DB.
I have a feeling that I am missing something.
I'm under the impression that IronWorker can use the databases for Heroku. I may be mistaken about this, however.
I can't claim a great deal of experience with cron tasks on Heroku, so forgive me if I get its limitations wrong. However, I'm under the impression that scaling from one dyno to many dynos is a little bit of a process. Where IronWorker shines is really in enabling the number of worker servers to fluctuate based on demand--you have the capacity to scale at a moment's notice, but are only paying for the scale you're actually using.
I have a Rails app running on heroku with Rufus Scheduler added on.
A 'once a day' task in the scheduler is running more often than once a day.
My guess would be something to do with the heroku app running on different dynos during the day, but I'm at a loss on how to confirm/fix the problem.
Has anyone else seen this/know of a solution?
Edit: I couldn't resolve the problem with the gem and have moved my app over to the heroku scheduler add on which does not experience this problem.
The Heroku scheduler isn't guaranteed, it's only a simple scheduling system designed to fill a gap. It's nothing to do with your application moving between dynos as it's a seperate management system spinning up one of processes.
If timeliness is essential to you, take a look at clockwork, which will let you configure all sorts of stuff, but also give you a bit more reliability (at the expense of having a clock process running).
If this won't do - simply rework your job so that it doesn't matter how often it runs.