When to scale out instance and when to scale out memory (EBS) inside the opensearch managed.

When deciding how to scale your OpenSearch managed cluster, it's important to consider the specific use case and performance requirements. Here's guidance on when to use each scaling approach:

1. Change instance type (Vertical Scaling):

• When you need more computational power (CPU) or memory per node
• If you're experiencing high CPU utilization or JVM memory pressure on individual nodes
• When you want to improve the performance of resource-intensive operations without adding more nodes

2. Change number of nodes (Horizontal Scaling):

• When you need to distribute your data and workload across more instances
• If you're approaching the storage limit of your current nodes
• To improve query performance by allowing more parallel processing
• When you want to increase the overall capacity of your cluster without changing instance types

3. Change the EBS volume size:

• When you need more storage capacity but don't necessarily need more computational resources
• If you're running out of disk space on your current volumes
• To accommodate data growth without adding more nodes or changing instance types

Specific use cases for each approach:

• Instance type change: Preferred when you have complex queries or aggregations that require more memory or CPU per node. This is also useful when you want to improve the performance of a smaller number of powerful nodes rather than managing many smaller nodes.

• Adding more nodes: Ideal when you need to scale out for better data distribution and query performance across a larger dataset. This approach is often used for handling increased ingestion rates or query loads by distributing the work across more nodes.

• Increasing EBS volume size: Best when your primary concern is storage capacity rather than computational power. This is useful for accommodating data growth in scenarios where your current instance types have sufficient CPU and memory, but you're running out of storage space.

It's worth noting that these scaling approaches are not mutually exclusive, and you may need to use a combination of them depending on your specific requirements and growth patterns. Additionally, OpenSearch managed now allows certain scaling operations without requiring a blue/green deployment, making it easier to adjust your cluster resources as needed.

Always monitor your cluster's performance metrics, such as CPU utilization, JVM memory pressure, and storage usage, to determine the most appropriate scaling strategy for your use case.
Sources
Scaling in Opensearch managed | AWS re:Post
Different ways of scaling in Opensearch managed. | AWS re:Post
Alternative to the blue green deployment in Opensearch | AWS re:Post
Amazon OpenSearch Service - Big Data Analytics Options on AWS

The optimal scaling approach depends on the specific bottleneck. Change instance type for CPU or memory bottlenecks. Change the number of nodes for overall capacity or resilience. Change the EBS volume size for storage capacity or disk I/O bottlenecks. Monitoring and iteration are crucial for effective scaling.

Highlights

• Monitoring is Key: Regularly monitor OpenSearch cluster metrics to identify bottlenecks.
• Start with Instance Type: Upgrading the instance type is often the easiest and most effective way to address CPU or memory bottlenecks.
• Consider Node Count for Capacity and Resilience: Adding nodes increases overall cluster capacity and improves fault tolerance.
• EBS Volume Size Impacts Storage and I/O: Increase EBS volume size for more storage and improved I/O performance.
• Iterate and Adjust: Scaling is an iterative process. Monitor performance after scaling and adjust the strategy as needed.
• Cost Considerations: Each scaling option has cost implications. Consider the cost of each option when making scaling decisions.

Above answer is correct. Additional Resources:- [+] How to scale up or scale out an OpenSearch Service domain - https://repost.aws/knowledge-center/opensearch-scale-up [+] Sizing Amazon OpenSearch Service domains - https://docs.aws.amazon.com/opensearch-service/latest/developerguide/sizing-domains.html