We use "a" before words that start with a consonant sound and "an" before words that start with a vowel sound. "EULA" seems to start with a semivowel sound.
An end-user license agreement (EULA, /ˈjuːlə/) is a legal contract entered into between a software developer or vendor and the user of the software, often where the software has been purchased by the user from an intermediary such as a retailer. A EULA specifies in detail the rights and restrictions which apply to the use of the software.
Do we right "a" or "an" before "EULA"?