Germany and the USSR (there was no independent Russia at that time) were not friendly in 1939. The Soviets signed the Molotov-Ribbentrop pact because they knew Germany planned to invade the USSR at some point, and they wanted to buy time.
It was a scurrilous, unprincipled deal (much like Poland's deal with Germany to divide up Czechoslovakia a year earlier), but the Soviets didn't make it because they were friends with Germany. They had actually preferred to sign an alliance with France, in order to protect Czechoslovakia, but that had failed due to a lack of willingness from France and a refusal by Poland to allow Soviet troops to cross Poland to reach Czechoslovakia (for some reasons that were understandable, given that the USSR and Poland had recently fought a war, and also because Poland itself wanted a piece of Czechoslovakia).
