One way to protect the origin in such a situation is never to allow requests to go to the origin in the first place. Instead, the origin itself populates the cache asynchronously when needed, as shown in Figure 11-7. If a cache miss is caused, this triggers an event that the origin can pick up on, alerting it that it needs to repopulate the cache. So if an entire shard has vanished, we can rebuild the cache in the background.
