Since 2009, Ukraine has no ambassador in Ethiopia; since 2014 - in Cuba and Montenegro; since 2015, there's no Ukrainian ambassador in Ireland. There are no ambassadors in Latvia and Croatia since 2016.
The offices of ambassadors in Tadzhikistan and Azerbaijan became vacant in autumn 2014.
Ukraine has no plans to assign the ambassador to Russia; there hasn't been one since 2015.
The ambassadors in foreign countries are appointed by the President of Ukraine; the candidacies are offered by the Foreign Minister. Both officials sign the respective decrees. Then, the diplomats go to the respective countries, carrying the credential letters.