You must have a passport with remaining validity minimum six months when you return from the trip. You also need to make sure that you are not running out of blank visa pages.It is mandatory for all foreign travellers with exception to the citizens of few countriesa to obtain the electronic travel authorization-in short ETA.
Electronic Travel Authorization is valid for 30 days from the date of issue. The application process for a Sri Lanka ETA visa is completely online and as long as you have a valid passport and credit card, you can apply for and receive an ETA Visa by filling out a simple form and pay the applicable fee by your credit card also please make sure that your passport has at least one blank page and validity date in your passport should be at least six months from the date of entry to Sri Lanka. And it is possible to extend your visa.
ETA Exemption: Citizens of Singapore, Maldives and Seychelles are exempt from the requirement of obtaining ETA and can obtain visa on arrival.
Diplomatic passport holders of Belarus, Chile, India, Indonesia, Iran, Kazakhstan, Nepal, Pakistan, Russia and Vietnam also do not require visa for Sri Lanka.
Citizens of the following 19 countries must obtain a visa in advance from one of the Sri Lankan diplomatic missions: Cameroon, Republic of the Congo, Democratic Republic of the Congo, Cote d'Ivoire, Egypt, Gabon, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Mali, Myanmar, Nigeria, North Korea, Sierra Leone, Sudan, Syria & Uganda