Ireland has been a party to the Hague Service Convention since 1994. Its Central Authority is the Master of the High Court in Dublin. Ireland objected to direct service by judicial officers and interested persons under Article 10(b) and (c), but its declaration expressly allows anyone involved in foreign proceedings, or their lawyer, to serve documents in Ireland directly through an Irish solicitor. Ireland has not objected to service by mail.
In practice, that makes service through an Irish solicitor, who arranges personal service and swears the proof, the usual route for U.S. litigants: it is typically much quicker than the Central Authority. Documents in English need no translation. A private process server acting on their own, without a solicitor's involvement, isn't covered by Ireland's declaration.