Cattle

Cattle are more representative of the instance types you should be running in public clouds such as Amazon Web Services (AWS) or Microsoft Azure, where you have auto scaling enabled.

• You have so many cattle in your herd you don't name them; instead they are given numbers and tagged so you can track them. In your instance cluster, you can also have too many to name so, like cattle, you give them numbers and tag them. For example, an instance could be called ip123067099123.domain.com and tagged as app-server.
• When a member of your herd gets sick, you shoot it, and if your herd requires it you replace it. In much the same way, if an instance in your cluster starts to have issues it is automatically terminated and replaced with a replica.
• You do not expect the cattle in your herd to live as long as a pet typically would, likewise you do not expect your instances to have an uptime measured in years.
• Your herd lives in a field and you watch it from afar, much like you don't monitor inpidual instances within your cluster; instead, you monitor the overall health of your cluster. If your cluster requires additional resources, you launch more instances and when you no longer require a resource, the instances are automatically terminated, returning you to your desired state.