Am I required to get rental car insurance if I don't have my own auto insurance?

I am planning to sell my car and cancel my auto insurance. If I want to rent a car, am I required to buy their rental car insurance, since I wouldn't have any other auto insurance otherwise?
Update: If I use my Discover card to rent the car, Discover will provide me with a Collision Damage Waiver of up to $25,000. Would that count as insurance?
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