From what I understand Vietnam had been fighting for a long time for their independence. From 1887 when France first colonized Vietnam to 1975 when Vietnam was finally unified. For the purpose of this question, I am only concerned with the time after the Communist Party of Vietnam was established (1930). Since the Soviet Union recognized the CPV's struggle to spread Communism, I am under the assumption that this is when they began to provide aid to the party, whether it be through monetary aid or supplies (such as firearms, food, etc).

The rebellion was already in full swing for nearly 3-4 years before China or Russia was able to get through. Vo Giap and so-on were already challenging the french in large pockets of the country through traditional guerrilla warfare. It was only in 1949 onwards that they begun to have access to artillery and Soviet/Chinese weapons once the Chinese revolution happened and they had border access.

I consider the main war for independence to have begun in 1940 when Japan invaded and annexed Vietnam from France in WW2. From my understanding, the armed wing of the CPV at the time: the Vietminh, received military aid from the Soviet Union, the Republic of China, and the U.S. through their Lend-Lease Act for the war against the Japanese. Then, during the 1st Indochina War against the French, the Soviet Union and the People's Republic of China continued to provide support through material aid and advisors. Then the Vietnam War with the U.S. where the both the previous Communist powers continued to provide support to Vietnam. I also understand that this was during the time of the Sino-Soviet Split between the U.S.S.R. and CCP, so both countries were trying be the main supporter of Vietnam by giving the most aid. My understanding is that Le Duan (the highest ranking man in the CPV behind Ho Chi Minh) and Vietnam preferred the U.S.S.R. over China due to a history of the latter conquering Vietnam multiple times. But regardless China still provided many weapons and supplies to Vietnam. This is all from my current understanding and knowledge, please let me know if any of my prior information is incorrect.

I'm not quite sure about which they preferred but there were pro-Chinese factions and pro-Russian factions. Vietnam tried to play off both against each-other in the ongoing Sino-Soviet split. The Soviets had better technical supplies and better high-tech equipment and the Warsaw Pact was very friendly with Vietnam but China had provided alot of more basic equipment. China was a bit different in insisting on more access and control of the Vietnamese government, in return for aid which the politburo very much despised. Sometime after Vietnam's victory China outrightly wanted Vietnam to join in on an anti-Russia coalition of communist nations, which they refused. Things went downhill and Vietnam signed an alliance with Russia instead.

For nearly 30 years of war, I imagine that a lot of money had to be poured into Vietnam in order to achieve independence. However, on the contrary to Communist belief, there is no free lunch. My question is how did post-war Vietnam pay back all of their debts to both Communist super powers? Does Vietnam still have debts to the modern Russian Federation since the fall of the Soviet Union? I've heard stories of Vietnam shipping people off to Russia to work in their factories in the 70's and 80's as a way of payment, but never anything concrete.

They didn't have to pay China back from my understanding, given they would later enter war with China in 79. The Chinese invasion partly was used to deliberately destroy alot of the industrial supplies China provided to Vietnam on the border areas, but they were essentially at hostilities until 1990 with both manning 500k-1m soldiers at the border, for the entirety of the 1980s. Vietnam expelled all the pro-China Maoists in its government that was put into place during the war. The Soviet Union and Vietnam continued receiving aid, given that Vietnam was fighting in Cambodia for a decade and essentially had complete control of Indochina through Laos and Cambodia. They provided port access at Cam Ranh Bay to Soviet warships for 2 decades and modern Russia as well. After the fall of the USSR, modern Russia cancelled all debts and continued leasing Cam Ranh Bay until this century when it reverted to Vietnam's control.

I don't think the stories of shipping people off is quite correct, they sent alot of students and workers to the Warsaw Pact nations though, and which is why there are Vietnamese communities through Central/Eastern Europe. This isn't really all that different from a labour exchange program.

Modern geopolitics is pretty much the same as the previous ideological one, Vietnam and Russia are still the closest in terms of military cooperation but instead Vietnam buys Russian weapons. There's an understanding that reliance on a foreign power shouldn't be done and they have already started diversifying to Israeli, Polish and other weapons and may start trying to get access to US weapons given the weapons embargo has been lifted.