Floating IP pattern

Another set of issues to tackle is that of a system without a load balancer. Suppose a single server exists with an external IP address to reach it. A new set of patches have come out, or a new release to the operating system core is required. The instance cannot stop responding to the external users or systems communicating with the instance, so the patches cannot be made in-place.

A traditional way to resolve this might be to change the DNS entry to a temporary instance that is not being upgraded. But this might cause issues if the external systems do not use the DNS entry, or have cached it and try to continue to talk to the instance being modified. The pattern that can be used to mitigate this is the floating IP pattern. In this pattern, an Elastic IP (EIP) is used and is assigned to the original server to be modified.

When the modifications are required, the instance is cloned using the stamp pattern and the EIP is assigned to that instance. This EIP is immediate...