Russia is not an ally, although they can be situationally allied with western interests at times when they have a certain level of influence and/or some internal interests that jive with ours.
That said, I'll go with the old saying "best to keep your friends close and your enemies closer". Russia is entirely capable of conducting mischief in its sphere of influence. They do, however, have a host of internal difficulties, economic and social, and a host of terror interests solely of their own making and focus. They're entirely unlikely to be expansionist at all, at least at this point in time.
Far more important is what China is doing in the North China Sea and in its sphere of influence - they are directly at odds, it seems, with much of the west's economic interests in the region and unless they are willing, and able, to do something related to North Korea, that could be a disaster area waiting to explode.