Hi Fabien,
For car rental at Dublin Airport in August, it is best to book in advance, as summer is a busy travel period. Booking early usually gives you more choice of vehicles and better rates.
Most major car hire companies operate from Dublin Airport, and you can find and compare available providers by searching online for car rental at Dublin Airport.
Our page on
renting a car in Ireland is also useful, with guidance on licences, insurance, booking ahead, toll roads, and driving tips to help you prepare.
Regards,
Eoin