Say you configure a cron job to run every minute to do something. What will happen if the actual task runs longer than a minute? Will cron create another job instance/thread? Or will cron wait and make sure the previous run is complete?
Thanks!
You must handle that scenario, not sure linux will handle it gracefully. By adding a simple check before running your task that the task is not already running. If you don't do that, hell will probably break loose on your server.
This post will help you Run cron job only if it isn't already running
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I'm creating a project in Node & Express that allows users to schedule the server to run test scripts e.g. once every ten minutes. I looked into node-schedule which looks great however it seems that all scheduled tasks disappear if the server ever restarts Node.
Cron looks good too but it has the problem that it doesn't seem to have a way to delete scheduled tasks after they have been set up.
If you were doing this, how would you go about it? I really don't want anything that's going to be complex, just need to schedule tasks, be able to delete individual tasks, and keep tasks in the event of a server reboot.
Simplest solution is to store the configurations for Cron in a database (since it takes a string as a parameter). Load the jobs from the db every time the app starts.
Just a quick question that has been bothering me today. I own five servers, all have the exact same image and run behind a load balancer. I want to run a process heavy cron on these servers every half an hour.
I don't want to put the cron on each machine, as it is resource heavy and would block all incoming connections for a good thirty seconds. In addition, I don't really want to put the cron on one machine, just to make sure it is redundant and it will be run.
My possible solutions to this would be to have a remote service that would run the cron, just by way of accessing a URL that would trigger it; I think that would be the most feasible at this point.
I'm really curious as to what other solutions might be available.
Thanks for your time!
You could set up staggered cron jobs on your 5 machines, so it runs every 2.5 hours on each of your 5 machines. Probably the cleanest way to do that is to schedule a job to run every 30 minutes, and have the job itself be a script that runs conditionally, depending on the current time and which machine it's on.
Or, if you have some kind of batch scheduling system, you could run a cron job on one system that submits a batch job, letting the scheduling system choose which server to use. This has the advantage that, assuming your batch system works properly, the job should still run if one of your servers is down. You'll likely need to set up some environment variables in your cron job to let it use the batch system properly.
Technology used: EJB 3.1, Java EE 6, GlassFish 3.1.
I need to implement a background job that is execute every 2 minutes to check the status of a list of servers. I already implemented a timer and my function updateStatus get called every two minutes.
The problem is I want to use a thread to do the update because in case the timer is triggered again but my function called is not done, i will like to kill the thread and start a new one.
I understand I cannot use thread with EJB 3.1 so how should I do that? I don't really want to introduce JMS either.
You should simply use and EJB Timer for this.
When the job finishes, simply have the job reschedule itself. If you don't want the job to take more that some amount of time, then monitor the system time in the process, and when it goes to long, stop the job and reschedule it.
The other thing you need to manage is the fact that if the job is running when the server goes down, it will restart automatically when the server comes back up. You would be wise to have a startup process that scans the current jobs that exist in the Timer system, and if yours is not there, then you need to submit a new one. After that the job should take care of itself until your deploy (which erases existing Timer jobs).
The only other issue is that if the job is dependent upon some initialization code that runs on server startup, it is quite possible that the job will start BEFORE this happens when the server is firing up. So, may need to have to manage that start up race condition (or simply ensure that the job "Fails fast", and resubmits itself).
Is it possible to check whether a SharePoint (actually WSS 3.0) timer job has run when it was scheduled to ?
Reason is we have a few daily custom jobs and want to make sure they're always run, even if the server has been down during the time slot for the jobs to run, so I'd like to check them and then run them
And is it possible to add a setting when creating them similar to the one for standard Windows scheduled tasks ... "Run task as soon as possible after a scheduled start is missed" ?
check it in job status page and then you can look at the logs in 12 hive folder for further details
central administration/operations/monitoring/timer jobs/check jobs status
As far as the job restart is concerned when it is missed that would not be possible with OOTB features. and it make sense as well since there are lot of jobs which are executed at particular interval if everything starts at the same time load on server would be very high
You can look at the LastRunTime property of an SPJobDefinition to see when the job was actually executed. As far as I can see in Reflector, the value of this property is loaded from the database and hence it should reflect the time it was actually executed.
I've seen that Heroku charges $15/mo to run Delayed Job, and $3/mo to run cron tasks daily. Is it possible to skip that entirely and run my own cron tasks manually? Or are they somehow figuring out that I'm running cron tasks?
I'm not entirely sure what you mean by "run my own cron tasks manually". For cron specifically, you need access to crontab, which they can control, as they're their servers. If you have another way of doing it, it would probably be fine, but bear in mind that your app is not tied to a specific server when running under Heroku, and that the server will change between executions.
Also, unless they've changed it since last time I checked, you can run daily cron tasks for free, but hourly costs $3/mo.
EDIT: Yes, daily crons are free. See http://addons.heroku.com/.
If you install the Heroku gem on your computer, you can then run your cron tasks manually as follows:
$ heroku rake cron
(in /disk1/home/slugs/xxxxxx_aa515b2_6c4f/mnt)
Running cron at 2010/04/25 10:28:54...
This will execute the exact same code as Heroku's daily/hourly cron add-on does; that is, for this to work, your application must have a Rakefile with a cron task, for example:
desc "Runs cron maintenance tasks."
task :cron do
puts "Running cron at #{Time.now.strftime('%Y/%m/%d %H:%M:%S')}..."
# TODO: your cron code goes here
end
Now, just add the heroku rake cron command to a crontab on any Unix server of yours, or even directly to your personal computer's crontab if you're running Linux or Mac OS X, and you can be scheduling cron jobs for your Heroku application as you please and without being charged for it.
Updating the answer for 2020:
You can use Heroku Scheduler which is Heroku's own add-on that lets you schedule commands using one-off dynos (so that you only pay for the run time of your jobs). The add-on itself is free, but doesn't really allow you to use cron but rather plain frequency: every day, every hour or every 10 minutes. Also, there's no guarantee that your job will execute at the scheduled time or at all..
There are other 3rd party add-ons that can help you run one-off dynos using cron expressions for better flexibility and are more resilient than Heroku Scheduler (proper disclosure, my company is the creator of one such add-on).
You can also use custom clock process (see here for more info) which essentially means that you have one dyno or process spawn tasks that run on other dynos. This usually costs more than using the aforementioned add-ons, but you have more granular control over your processes and since you only rely on Heroku, it may be more stable.
Yes, I've successfully used a cron job on my local server which essentially runs
$ heroku rake <rake task>
at whatever intervals I've required. I've used in on both aspen and bamboo stacks.
You can also just install a gem like rufus-scheduler if you're running a rails app and setup scheduling that way. I don't know if this is bad practice for some reason, but it's what I do with my app, and it seems to work fine.
If you want to have scheduled jobs you can also use http://guardiano.getpeople.in that is a free service (for 10 jobs) for job scheduling.
You just need to setup an HTTP endpoint in your application to recieve event notifications on POST or GET and you can also set some additional params to prevent not authorized actions.
So you set a job in Guardiano that will cal http://yourapp.com/youraction and leave "minutes" blank if you want you action to run once in the future or set minutes to what you want to run your action every X minutes. In that way you only have to create your endpoint for you app and when this EP is called you execute something.
So your app can sleep and you don't need to spend money and time setting up jobs and taking care that they are working properly.
IMHO if you need something fast for an MVP or you need to setup a lot of jobs for different apps than a free service like that where you can actually outsource cronjobs is quite good.
There was aslo an Heroku Addon called Temporize to do that but I'm not sure is still alive and working