Different ways of scaling in Opensearch managed.

Amazon OpenSearch Service (managed) offers multiple ways to scale your clusters to accommodate growing data and traffic demands:

1. Horizontal Scaling: You can add more nodes to your OpenSearch domain. This allows you to distribute your data and workload across additional instances, improving performance and capacity. The default maximum is 20 data nodes per domain, but you can request a service limit increase up to 100 instances per domain.

2. Vertical Scaling: You can modify the instance types to larger, more powerful ones. This increases the computational resources (CPU, memory) available to each node, which can improve performance for resource-intensive operations.

3. Storage Scaling: You can increase the size of the Amazon EBS volumes associated with your instances. Each instance can have one EBS volume with a maximum size of 1.5 TB. This allows you to accommodate data growth without necessarily adding more nodes.

4. UltraWarm Storage: For less frequently accessed data, you can use UltraWarm storage, which offers a cost-effective way to store large amounts of read-only data using Amazon S3 and a sophisticated caching solution.

It's worth noting that OpenSearch Service allows you to scale your domain without downtime. You can write code to monitor your domain's state through Amazon CloudWatch metrics and use the OpenSearch Service API to scale your domain up or down based on thresholds you set.

When scaling, keep in mind that with the maximum of 100 instances per domain (after a service limit increase), you can allocate about 150 TB of EBS storage to a single domain.

These scaling options provide flexibility in managing your OpenSearch clusters, allowing you to optimize for performance, capacity, and cost based on your specific workload requirements.
Sources
Amazon OpenSearch Service - Big Data Analytics Options on AWS
Open-Source Search Engine - Amazon OpenSearch Service Managed Service - AWS