Hello everyone.  I am about to move from a shared hosting environment where I run LS to a cloud-based solution.  I have some burst traffic issues that was causing timeouts in the shared environment and cloud resources are amazingly cheap as someone who has not looked into it for five years.

So running LS 5 I am thinking two servers, one for apache/php and the other for mysql.  My question: does anyone have experience planning cloud server capacity for a setup like this?  My initial thought (comparing to when I was running servers under my desk) is that 1-vcpu 2GB RAM for each server would get me through.  Nothing else will be running there, but my challenge will be burst traffic through LS starting about 50 survey sessions/min for 6 hours.

So it is not unbelievably large, but the shared host I was on was doing 550 queries/sec when my site was idle and it started timing out after 15 seconds of my load test.  My main goal is that it not leave a lot of people hanging while it times out.

I know that there is a cloud hosted option through LS, but the pricing model (based on responses/year) it not realistic for my use case. (This is for organization-wide data collection during a very small window, shorter versions will be repeated at future dates hence my self-hosting versus pay per response.)  Thanks for any insight based on your experiences..  ck

 

[Disclaimer: No server expert here]

For Limesurvey I think I would go with more RAM, especially as it is not so expensive anyway.

I personally would probably not go with two servers, but I guess you have your reasons.

I think the biggest bottleneck with Limesurvey are the big session files. So you should be prepared for that.

But all of this of course depends heavily on your survey structure. Are those 50 survey sessions per minute "started" or "concurrent"?

Because if it is 50 per minute started, the number of concurrent surveys might be more or less, depending on how long the survey takes.

For a 1 minute survey, this doesn't matter, but if your survey takes on average about 20 minutes to finish, then 50 people starting a survey session will quickly create a big number of people that are filling the survey at the same time and the peak would be probably by more than 1000 at a certain point.

Also, I think if you use equations quite heavily, this can also require "more power". As you say, VPS/cloud hosting is relatively cheap, so i would rather overpower this setup a bit.

Also, in general in research we do send out the invitations in batches over a a couple of days to keep bursts down, you might think about that. I don't know the exact requirements, so this might not be an option, but generally it is not a big deal if some are invited a couple of days later than others.

So if you can spread the invitations out over 2-3 days, you can probably reduce the load significantly and make the survey taking experience more pleasant for everyone. But as I said, might not be an option for your specific case.

On a side note: I am sure the guys from Limesurvey GmbH would make you a customized offer.

But of course, going for self-hosting is also an option, if you know what you are doing.