Random problems with server communication

[niloofarmansoor]

I have two magpie applications hosted on netlify and I have a server on heroku to receive my submissions. My applications work fine most of the time, but sometimes I randomly get this error when I open them:

Sorry, there is an error communicating with our server and the experiment cannot proceed. Please return the HIT immediately and contact the author at “email” Please include the following error message: "undefined". Thank you for your understanding

Is there anything I can do to increase the reliability of the app? Does this have anything to do with my heroku server? (I set it up according to your instructions). I’m using these apps as part of a survey and I want to be sure that this issue doesn’t rise.

[x-ji]

Hi, you could install Papertrail on your Heroku app by following the instructions at https://elements.heroku.com/addons/papertrail, then you can inspect the logs on the server when this happens from the Heroku UI.

Sometimes it might happen when there haven't been any experiments submissions for a long time, and the server needs some time to start up again, since Heroku free tier servers will sleep after a certain amount of time of not being used. What we usually do is to pre-start the server by simply visiting the server UI (experiment management page), before we start a round of experiments.

Sometimes this would happen when the experiment is set to "inactive" for some reason.

If you're doing interactive experiments, this might happen when the sum of (previous submissions + the number of current participants) has exceeded the (chain * realization * variant) total. Of course this shouldn't be an issue for normal experiments.

[x-ji]

If you could successfully set up the logging, please post the server logs at the moment when the error happened, and we could take a look into that.