When using a smart client, the client library provides an interface to the cluster, and performs server selection directly via the vBucket mechanism. The clients communicate with the cluster using a custom Couchbase protocol which enables the sharing of the vBucket map, and the selection within the client of the required vBucket when obtaining and storing information.

Figure 4.4. Deployment Strategy — Using a vBucket Aware Client

See also vBuckets for an in-depth description.