As we will see in the next sections, sharding is complicated and expensive, operation wise. It is important to plan ahead and make sure that we start the sharding process long before we hit our system's limits.

Some rough guidelines on when you need to start sharding are as follows:

• When you have a CPU utilization of less than 70% on average
• When I/O (and especially write) capacity is less than 80%
• When memory utilization is less than 70% on average

As sharding helps with write performance, it's important to keep an eye on our I/O write capacity and the requirements of our application.