If the trip lasts more than 15 days, then you need to issue a visa.

In case the stay in Vietnam exceeds 15 days, a visa is issued. For a visa it is necessary to arrange a visa invitation in advance (it is made out in the tourist company, only passport data is provided). The cost and terms of issuing the visa invitation are specified in the travel company. If you forget to issue a visa, you may be asked to pay a fine at the border, but what will happen if you forget about it is ±. $

You need a visa for a trip. It can be issued in Moscow or on arrival (visa support is needed). More details on the page "Visa to Vietnam".