My 2 cents:

If you decide to do your processing jobs on frontend, do use a non-default 
version. What I found out off of my experiments is that app latency takes 
an important role in scheduler decisions (e.g. when to launch new instances 
or wait for some to free up, etc) Actually, it makes a lot of sense. This 
is definitely one of the factors consider while autoscaling after all.

If you do your background processing, i.e. something not directly connected 
to your app users (if any), *and* respond to users' actions, all from the 
same app version (or a backend), this might have a negative impact on your 
app's UX. But, if you do run all of the stuff on the same app 
version/backend, please don't scream "why AE does not use my single 
instance like I told it so. fix it, google" on this forum, because you will 
likely be seeing an unexpected number of instances being spun up and shut 
down.

I might be wrong here but this is one of the things I took out of my 
experience running apps on AE.

-- alex.


On Saturday, April 21, 2012 2:15:00 PM UTC+2, Strom wrote:
>
> 1. If you always have only one request running at a time then 3 
> instances sounds bad indeed. 
> 2. Backends are decent, but more expensive. You can probably get the 
> same work done on a frontend instance, but cheaper. 
> 3. Cron is unreliable, use the task queue instead. 
>
> On Apr 20, 10:00 pm, Ido Ran <[email protected]> wrote: 
> > Hi, 
> > I'm writing an application that read messages from twitter on GAE. The 
> > application should read messages all the time and react to them. 
> > Because I'm currently testing an idea I don't want to use backends, 
> which 
> > are the natural choice for such need. 
> > I'm using a cron job that run every minute and servlet which handle the 
> job 
> > by running for as long as 50 seconds continually reading messages. 
> > 
> > 1. I've notice that GAE open up to 3 instances to handle only this 
> trafic, 
> > is that bad? 
> > 2. Backends are the right tool for such job, right? 
> > 3. Is there better way of doing it without backends? 
> > 
> > Thank you.

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