Allows you to purchase a reserved cache node offering. Reserved nodes are not eligible for cancellation and are non-refundable. For more information, see <a href="https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/reserved-nodes.html">Managing Costs with Reserved Nodes</a> for Redis or <a href="https://docs.aws.amazon.com/AmazonElastiCache/latest/mem-ug/reserved-nodes.html">Managing Costs with Reserved Nodes</a> for Memcached.