Officially, the second generation Apple TV is not obsolete; even the oldest first generation Apple TV is classified as "vintage" rather than obsolete by Apple. However, Apple's introduction of the App Store on the fourth generation TV has Cult of Mac writers suggesting that previous models are practically obsolete.
The second generation Apple TV was discontinued when the third generation model was released in March 2012. The third generation model was itself discontinued a year later in March 2013. The second generation Apple TV's last software update was Apple TV Software 6.2.1, which is based on iOS 7.1.2, and it cannot be updated beyond this point.