Cloud Computing introduces new challenges for performance analysis, for both customers and operators of the cloud. Apart from monitoring a scaling environment, issues within a system can be complicated when tenants are competing for the same resources, and are invisible to each other. Other factors include rapidly changing production code and wildly unpredictable traffic surges. For performance analysis in the Joyent public cloud, we use a variety of tools including Dynamic Tracing, which allows us to create custom tools and metrics and to explore new concepts. I'll discuss a collection of these tools and the metrics that they measure. While these are DTrace-based, the focus of the talk is on which metrics are proving useful for analyzing real cloud issues.