Ukraine

Without a doubt. However, and take this with a grain of salt, Russian troops simply may not know where they are being sent. There are accounts from soldiers that they believed they were being sent to training when in reality, they were dumped on the front lines with no warning. They are told to attack, or get shot by their own troops if they try to retreat. Regardless, their chances of survival are extremely low.

Also, If you hold a newly recruited soldier in relative isolation for a bit, ship them around a few times to different places and keep telling them lies about what is happening, it's fairly easy just to dump them into a war zone the next day with little warning without much resistance.

This probably only scratches the surface of what is actually going on and I personally haven't been there to see this with my own eyes.

However, your question still remains: Why haven't they revolted? Ignoring any second hand accounts or my speculation, simple explanations are that they simply do not know the truth and scope of the situation, are being persuaded or forced, they don't know where they are, or, they actually want to be there. You can believe what you choose to believe.