Yes, a valid credit card is required, however you won't be charged as long as you do not exceed your free trial quota.  You may also choose Paypal however when such payment method is selected, you will be required to pre-pay US$30 or S$15 or A$15 worth of credits upfront (with validity for 13 months). Pre-paid Public Cloud credits are non-refundable.  Once the voucher has been activated in the holder’s customer account, it is valid for a period of one (1) month, and is automatically deducted from the bills linked to the Public Cloud project for which the voucher has been activated.