MartinEdic, Moldova is NOT part of NATO.
Putin has used much the same tactics towards it as Ukraine. Essentially setting up Russian separatists in the Transnistria part of the country. Putin keeps leverage over Modovia by supplying it with oil. The price rises with the country wanting to do more business with the West.
The expansion of NATO is a thorn in Putin's side but perhaps not the real motivation for his invasion of Ukraine.
The first reason is simple mobster stuff. That he wanted Ukraine answering to him and paying rent. When Ukraine wanted out of this relationship, it was threatened to comply. When this failed to work Putin had to punish Ukraine into submission. When this even this didn't work Ukraine had to be killed. As I say mobster stuff.
The other motivation is retirement. Autocrats historically have a problem of not being able to. That is with keeping ones head and loot.
If the second explanation weighs heavily with Putin. That is a way out of this bloodshed. Give him security and some of his accumulated loot. Of course this vomit inducing solution would have to be sold to the parties -- including Putin.
Putin was after the big splash. He had that with Ukraine. Moldova, as you say, is very small fish.
Many thanks.