Roost joined the Scouts Battalion in 2010, where he served until 2017. As part of the Scouts Battalion, he participated in foreign operations in Afghanistan in 2011 and 2013. In 2017, he went through the selection process of the Special Operations Forces (ESTSOF), joined the unit and in 2020 participated in a foreign operation in Mali. Roost served in ESTSOF until 2023, when he voluntarily left the service. After that, he went to volunteer in Ukraine, where he fought in the ranks of the 3rd Regiment of the Special Operations Forces.