In a deal brokered by the United States, Ukraine will be selling $2.4 billion worth of weapons to Iraq. Most of these will be of Russian design, which many Iraqi military personnel are familiar with. Ukraine has, and still manufactures, lots of Russian designed weapons.
Ukraine split from the Soviet Union (and Russia) in 1991 when the Soviet Union was dissolved. Many Soviet weapons plants were in Ukraine, as well as huge quantities of military equipment. That's because Ukraine was the forward staging area for Soviet forces that were to invade Western Europe, or defend against NATO.
Ukraine inherited whatever was on its territory when the dissolution took place. Ukraine has kept some of those weapons plants going by becoming the low-cost provider of new Russian designed weapons (and now much of those have been updated by Ukrainian engineers.)
While friendly with the United States, Ukraine has also cultivated good relations with China, by quietly sending the Chinese examples of advanced Soviet weapons (including some that never went into mass production). Ukraine wants to be on good terms with the U.S. and China because of the fear that Russian will try to make Ukraine, once more, part of Russia. This first happened in the 17th century, and the Ukrainians never got used to it. Actually, Ukraine had been dismembered before that by Poles, Lithuanians and Mongols. Thus Ukraine is enjoying its first period of real independence in over 500 years. They want to keep it that way.