Information Technology industry. Cloud environment is susceptible to attacks or intrusions, but it has to be safe and reliable for its users, to provide them secure access. Intrusion Tolerant is one of the techniques that can prevent such intrusions so the evaluation of this technique need to stay up-to-date with the ever advancing system attacks in order to prevent possible system failures. The search for the ideal system which is intrusion-aware, fault-tolerant and recovery-capable has presented many architecture typologies. The goal of this paper is to present some of these typologies and, along with their strongholds, attach a critical view with focus on their weakest spots.