I plan to insert some initialization code into OnStart() method of my class derived from RoleEntryPoint. This code will make some permanent changes to the host machine, so in case it is run for the second time on the same machine it will have to detect those changes are already there and react appropriately and this will require some extra code on my part.
Is it possible OnStart() is run for the second time before the host machine is cleared? Do I need this code to be able to run for the second time on the same machine?
Is it possible OnStart() is run for
the second time before the host
machine is cleared?
Not sure how to interpret that.
As far as permanent changes go: Any installed software, registry changes, and other modifications should be repeated with every boot. If you're writing files to local (non-durable storage), you have a good chance of seeing those files next time you boot, but there's no guarantee. If you are storing something in Windows Azure Storage (blobs, tables, queues) or SQL Azure, then your storage changes will persist through a reboot.
Even if you were guaranteed that local changes would persist through a reboot, these changes wouldn't be seen on additional instances if you scaled out to more VMs.
I think the official answer is that the role instance will not run it's Job more than once in each boot cycle.
However, I've seen a few MSDN articles that recommend you make startup tasks idempotent - e.g. http://msdn.microsoft.com/en-us/library/hh127476.aspx - so probably best to add some simple checks to your code that would anticipate multiple executions.
Related
I've just learned how to use notifications and subscriptions in Chef to carry out actions such as restarting services if a config file is changed.
I am still learning chef so may just have not got to this section yet but I'd like to know how to do the actions conditionally.
Eg1 if I change a config file for my stand alone apache server I only want to restart the service if we are outside core business hours ie the current local time is between 6pm and 6am. If we are in core business hours I want the restart to happen but at a later time, outside core hours.
Eg2 if I change a config file for my load balanced apache server cluster I only want restart the service if a) the load balancer service status is "running" and b) all other nodes in the cluster have their apache service status as running ie I'm not taking down more than one node in the cluster at once.
I imagine we might need to put the action in a ruby block that either loops until the conditions are met or sets a flag or creates a scheduled task to execute later but I have no idea what to look for to learn how best to do this.
I guess this topic is kind of philosophical. For me, Chef should not have a specific state or logic beyond the current node and run. If I want to restart at a specific time, I would create a cron job with a conditional and just set the conditional with chef (Something like debian's /var/run/reboot-required). Then crond would trigger the reboot.
For your second example, the LB should have no issues to deal with a restarting apache backend and failover to another backend. Given that Chef runs regulary with something called "splay" the probability is very low that no backend is reachable. Even with only 2 backends. That said, reloading may be the better way.
The instance started to fail on mysql... the mysql stops from nowhere. Then i was re-starting it and it worked again.
But now, it got worse. The transfer rate when i download a file from another instante starts in 900kbps and keep going down till 20kbps. Also for external downloads.
I tested also a zip job, zipping a big file.... it starts quickly then it slows down and keeps a rate of 10 files zipped per second wich is too slow ( another instances gets 1000 files per sec).
I can't access trough http the websites hosted also because its too slow.
I have already reboot, stop->start. Also i made an image e rebuild the image in a new instance and the problem continues. I also changed the Volume used by the instance and the volume with the problem keeps slow.
What should i do?
I'll take a stab (based on the lack of details), that your instance is just to small - sounds like you are running a web server and mysql on it at least, I'll also bet that you are trying to use a micro instance which have notoriously variable performance statistics and really aren't suitable for running a web server and database server with consistent performance (maybe ok for development, but not production imo).
Try just spinning up a larger instance and see if your problems magically go away; you can test this for a few dollars and if it does solve the problem you can decide if you can permanently upgrade the image size.
The issue I have is that I'm using a third party dll for something (very expensive operation), it's not serializable, and it takes a minute to spin up each time. It's needed on each call of a WCF service and I can't keep it in memory (recyling), and I can't keep it in a cache (unserializable).
I was wondering what alternatives (if any) there are? I was originally thinking about using a Worker Role, but then I read that they are recycled too. Then I considered a Windows service, but I'm hoping there is something better suited.
I'd like to think I'm not the only one with this issue, and that someone else has already solved this issue! :)
Why are you unable to use Worker Roles or Web Roles to keep the data generated by yoru process in memory? Neither of the two roles "flushes" it's memory on a frequent basis. True, that it is not guaranteed that reboots do not happen, but those reboots are very rare and checking to see IF your statefull data is empty and then repopulating it when it is, shouldnt be a big deal and the logic would work on any server the same way, whether it is a Cloud Service or a dedicated VM.
Edit: Web roles or worker roles do not restart on any known cycle. However, by default IIS does recycle on a schedule. This timer can be changed or disabled via a startup script.
Furthermore, no such recycling happens in worker roles. So, if you're running a worker role, the thing will stay in memory as long as you dont recycle the server yourself or a rare windows update happens
HTH
Here's my scenario: my Azure web role does a lot of work in OnStart() and produces a huge debug trace that is uploaded to Blob Storage.
Now OnStart() hangs for whatever reason and I look into Blob Storage and see that trace has not been updated for several minutes already. So I decide the role is beyond repair and I want to shut it down immediately so that I can update the role with another package and start it again.
The problem is when I hit "Stop" in the Management Portal it takes up to ten minutes to stop the role - I guess it tries to convince the role to stop gracefully and wait for several minutes.
Can I somehow make the role stop immediately without letting it stop gracefully?
I wonder if deleting the deployment (that's presumably what you're going to do after stopping it?) is faster, but I'm not sure. As far as I know, there's only one kind of "stop," so no, I don't think there's a way to force a faster stop.
Have a look # Windows Azure Platform PowerShell Cmdlets
It should give you at least the same functionality and probably more control over the actions. You could also request the current status as it is not always reflected immediately in the Silverlight portal.
Suppose my Azure role is notified that it will be terminated soon and technically can clean up local resources after itself (temporary files for example). Should it do so?
I'm not asking about whether someone will see my leftover temporary files - just how my role can be a polite good Azure citizen.
Does it make sense for the role to clean up local resources or should it just leave everything as is?
Like Stuart said, there's no reason to do any local storage cleanup. You either leave it for yourself to use in the future (which is not guaranteed), or you have the local storage cleaned up automatically after your role instance shuts down.
What you do want to do during shutdown is relesae blob leases, close open sessions, shut down database connections, etc. You won't have this opportunity if the Guest OS (or Host OS) crashes, but you always want to handle graceful shutdowns when possible.
I can't think of any good reason why you should clean up things like temporary files during this shutdown.
Instead I just use the notification as a graceful way to shutdown - hopefully avoiding leaving any jobs "half-finished".
For the issue of temporary files in particular, the LocalStorage feature has a "Clean on Role Recycle" property - you should probably set that to true.