Google Colaboratory: 'No backend with GPU available'. Why is this?

Question

I\'m using Google Colabs GPU to train multiple Convolutional Neural Networks. It\'s been going relatively fine but since yesterday I get a message that says there is \'no ba

Answer 1

Edit: As of February, 2020, the FAQ has been updated with much more information on usage limits and a pointer to Colab Pro for users in need of higher limits.

My original answer follows.

Seems to be answered by the FAQ.

Quoting:

How may I use GPUs and why are they sometimes unavailable?

Colaboratory is intended for interactive use. Long-running background computations, particularly on GPUs, may be stopped. Please do not use Colaboratory for cryptocurrency mining. Doing so is unsupported and may result in service unavailability. We encourage users who wish to run continuous or long-running computations through Colaboratory’s UI to use a local runtime.

It seems that limits on GPU access are periodically reset, so you're likely to be able to access a GPU again later after waiting for some time for cooldown.