When you use Amazon OpenSearch Service for time-bound data like server logs, service logs, application logs, clickstreams, or event streams, storage cost is one of the primary drivers for the overall cost of your solution. Over the last year, OpenSearch Service has released features that have opened up new possibilities for storing your log data in various tiers, enabling you to trade off data latency, durability, and availability. In October 2023, OpenSearch Service announced support for im4gn data nodes, with NVMe SSD storage of up to 30 TB. In November 2023, OpenSearch Service introduced or1, the OpenSearch-optimized instance family, which delivers up to 30% price-performance improvement over existing instances in internal benchmarks and uses Amazon Simple Storage Service (Amazon S3) to provide 11 nines of durability. Finally, in May 2024, OpenSearch Service announced general availability for Amazon OpenSearch Service zero-ETL integration with Amazon S3. These new features join OpenSearch’s existing UltraWarm instances, which provide an up to 90% reduction in storage cost per GB, and UltraWarm’s cold storage option, which lets you detach UltraWarm indexes and durably store rarely accessed data in Amazon S3.
This post works through an example to help you understand the trade-offs available in cost, latency, throughput, data durability and availability, retention, and data access, so that you can choose the right deployment to maximize the value of your data and minimize the cost.
Examine your requirements
When designing your logging solution, you need a clear definition of your requirements as a prerequisite to making smart trade-offs. Carefully examine your requirements for latency, durability, availability, and cost. Additionally, consider which data you choose to send to OpenSearch Service, how long you retain data, and how you plan to access that data.
For the purposes of this discussion, we divide OpenSearch instance storage into two classes: ephemeral backed storage and Amazon S3 backed storage. The ephemeral backed storage class includes OpenSearch nodes that use Nonvolatile Memory Express SSDs (NVMe SSDs) and Amazon Elastic Block Store (Amazon EBS) volumes. The Amazon S3 backed storage class includes UltraWarm nodes, UltraWarm cold storage, or1 instances, and Amazon S3 storage you access with the service’s zero-ETL with Amazon S3. When designing your logging solution, consider the following:
- Latency – if you need results in milliseconds, then you must use ephemeral backed storage. If seconds or minutes are acceptable, you can lower your cost by using Amazon S3 backed storage.
- Throughput – As a general rule, ephemeral backed storage instances will provide higher throughput. Instances that have NVMe SSDs, like the im4gn, generally provide the best throughput, with EBS volumes providing good throughput. or1 instances take advantage of Amazon EBS storage for primary shards while using Amazon S3 with segment replication to reduce the compute cost of replication, thereby offering indexing throughput that can match or even exceed NVMe-based instances.
- Data durability – Data stored in the hot tier (you deploy these as data nodes) has the lowest latency, and also the lowest durability. OpenSearch Service provides automated recovery of data in the hot tier through replicas, which provide durability with added cost. Data that OpenSearch stores in Amazon S3 (UltraWarm, UltraWarm cold storage, zero-ETL with Amazon S3, and or1 instances) gets the benefit of 11 nines of durability from Amazon S3.
- Data availability – Best practices dictate that you use replicas for data in ephemeral backed storage. When you have at least one replica, you can continue to access all of your data, even during a node failure. However, each replica adds a multiple of cost. If you can tolerate temporary unavailability, you can reduce replicas through or1 instances, with Amazon S3 backed storage.
- Retention – Data in all storage tiers incurs cost. The longer you retain data for analysis, the more cumulative cost you incur for each GB of that data. Identify the maximum amount of time you must retain data before it loses all value. In some cases, compliance requirements may restrict your retention window.
- Data access – Amazon S3 backed storage instances generally have a much higher storage to compute ratio, providing cost savings but with insufficient compute for high-volume workloads. If you have high query volume or your queries span a large volume of data, ephemeral backed storage is the right choice. Direct query (Amazon S3 backed storage) is perfect for large volume queries for infrequently queried data.
As you consider your requirements along these dimensions, your answers will guide your choices for implementation. To help you make trade-offs, we work through an extended example in the following sections.
OpenSearch Service cost model
To understand how to cost an OpenSearch Service deployment, you need to understand the cost dimensions. OpenSearch Service has two different deployment options: managed clusters and serverless. This post considers managed clusters only, because Amazon OpenSearch Serverless already tiers data and manages storage for you. When you use managed clusters, you configure data nodes, UltraWarm nodes, and cluster manager nodes, selecting Amazon Elastic Compute Cloud (Amazon EC2) instance types for each of these functions. OpenSearch Service deploys and manages these nodes for you, providing OpenSearch and OpenSearch Dashboards through a REST endpoint. You can choose Amazon EBS backed instances or instances with NVMe SSD drives. OpenSearch Service charges an hourly cost for the instances in your managed cluster. If you choose Amazon EBS backed instances, the service will charge you for the storage provisioned, and any provisioned IOPs you configure. If you choose or1 nodes, UltraWarm nodes, or UltraWarm cold storage, OpenSearch Service charges for the Amazon S3 storage consumed. Finally, the service charges for data transferred out.
Example use case
We use an example use case to examine the trade-offs in cost and performance. The cost and sizing of this example are based on best practices, and are directional in nature. Although you can expect to see similar savings, all workloads are unique and your actual costs may vary substantially from what we present in this post.
For our use case, Fizzywig, a fictitious company, is a large soft drink manufacturer. They have many plants for producing their beverages, with copious logging from their manufacturing line. They started out small, with an all-hot deployment and generating 10 GB of logs daily. Today, that has grown to 3 TB of log data daily, and management is mandating a reduction in cost. Fizzywig uses their log data for event debugging and analysis, as well as historical analysis over one year of log data. Let’s compute the cost of storing and using that data in OpenSearch Service.
Ephemeral backed storage deployments
Fizzywig’s current deployment is 189 r6g.12xlarge.search data nodes (no UltraWarm tier), with ephemeral backed storage. When you index data in OpenSearch Service, OpenSearch builds and stores index data structures that are usually about 10% larger than the source data, and you need to leave 25% free storage space for operating overhead. Three TB of daily source data will use 4.125 TB of storage for the first (primary) copy, including overhead. Fizzywig follows best practices, using two replica copies for maximum data durability and availability, with the OpenSearch Service Multi-AZ with Standby option, increasing the storage need to 12.375 TB per day. To store 1 year of data, multiply by 365 days to get 4.5 PB of storage needed.
To provision this much storage, they could also choose im4gn.16xlarge.search instances, or or1.16.xlarge.search instances. The following table gives the instance counts for each of these instance types, and with one, two, or three copies of the data.
| . | Max Storage (GB) per Node |
Primary (1 Copy) |
Primary + Replica (2 Copies) |
Primary + 2 Replicas (3 Copies) |
| im4gn.16xlarge.search | 30,000 | 52 | 104 | 156 |
| or1.16xlarge.search | 36,000 | 42 | 84 | 126 |
| r6g.12xlarge.search | 24,000 | 63 | 126 | 189 |
The preceding table and the following discussion are strictly based on storage needs. or1 instances and im4gn instances both provide higher throughput than r6g instances, which will reduce cost further. The amount of compute saved varies between 10–40% depending on the workload and the instance type. These savings do not pass straight through to the bottom line; they require scaling and modification of the index and shard strategy to fully realize them. The preceding table and subsequent calculations take the general assumption that these deployments are over-provisioned on compute, and are storage-bound. You would see more savings for or1 and im4gn, compared with r6g, if you had to scale higher for compute.
The following table represents the total cluster costs for the three different instance types across the three different data storage sizes specified. These are based on on-demand US East (N. Virginia) AWS Region costs and include instance hours, Amazon S3 cost for the or1 instances, and Amazon EBS storage costs for the or1 and r6g instances.
| . |
Primary (1 Copy) |
Primary + Replica (2 Copies) |
Primary + 2 Replicas (3 Copies) |
| im4gn.16xlarge.search | $3,977,145 | $7,954,290 | $11,931,435 |
| or1.16xlarge.search | $4,691,952 | $9,354,996 | $14,018,041 |
| r6g.12xlarge.search | $4,420,585 | $8,841,170 | $13,261,755 |
This table gives you the one-copy, two-copy, and three-copy costs (including Amazon S3 and Amazon EBS costs, where applicable) for this 4.5 PB workload. For this post, “one copy” refers to the first copy of your data, with the replication factor set to zero. “Two copies” includes a replica copy of all of the data, and “three copies” includes a primary and two replicas. As you can see, each replica adds a multiple of cost to the solution. Of course, each replica adds availability and durability to the data. With one copy (primary only), you would lose data in the case of a single node outage (with an exception for or1 instances). With one replica, you might lose some or all data in a two-node outage. With two replicas, you could lose data only in a three-node outage.
The or1 instances are an exception to this rule. or1 instances can support a one-copy deployment. These instances use Amazon S3 as a backing store, writing all index data to Amazon S3, as a means of replication, and for durability. Because all acknowledged writes are persisted in Amazon S3, you can run with a single copy, but with the risk of losing availability of your data in case of a node outage. If a data node becomes unavailable, any impacted indexes will be unavailable (red) during the recovery window (usually 10–20 minutes). Carefully evaluate whether you can tolerate this unavailability with your customers as well as your system (for example, your ingestion pipeline buffer). If so, you can drop your cost from $14 million to $4.7 million based on the one-copy (primary) column illustrated in the preceding table.
Reserved Instances
OpenSearch Service supports Reserved Instances (RIs), with 1-year and 3-year terms, with no up-front cost (NURI), partial up-front cost (PURI), or all up-front cost (AURI). All reserved instance commitments lower cost, with 3-year, all up-front RIs providing the deepest discount. Applying a 3-year AURI discount, annual costs for Fizzywig’s workload gives costs as shown in the following table.
| . | Primary | Primary + Replica | Primary + 2 Replicas |
| im4gn.16xlarge.search | $1,909,076 | $3,818,152 | $5,727,228 |
| or1.16xlarge.search | $3,413,371 | $6,826,742 | $10,240,113 |
| r6g.12xlarge.search | $3,268,074 | $6,536,148 | $9,804,222 |
RIs provide a straightforward way to save cost, with no code or architecture changes. Adopting RIs for this workload brings the im4gn cost for three copies down to $5.7 million, and the one-copy cost for or1 instances down to $3.2 million.
Amazon S3 backed storage deployments
The preceding deployments are useful as a baseline and for comparison. In actuality, you would choose one of the Amazon S3 backed storage options to keep costs manageable.
OpenSearch Service UltraWarm instances store all data in Amazon S3, using UltraWarm nodes as a hot cache on top of this full dataset. UltraWarm works best for interactive querying of data in small time-bound slices, such as running multiple queries against 1 day of data from 6 months ago. Evaluate your access patterns carefully and consider whether UltraWarm’s cache-like behavior will serve you well. UltraWarm first-query latency scales with the amount of data you need to query.
When designing an OpenSearch Service domain for UltraWarm, you need to decide on your hot retention window and your warm retention window. Most OpenSearch Service customers use a hot retention window that varies between 7–14 days, with warm retention making up the rest of the full retention period. For our Fizzywig scenario, we use 14 days hot retention and 351 days of UltraWarm retention. We also use a two-copy (primary and one replica) deployment in the hot tier.
The 14-day, hot storage need (based on a daily ingestion rate of 4.125 TB) is 115.5 TB. You can deploy six instances of any of the three instance types to support this indexing and storage. UltraWarm stores a single replica in Amazon S3, and doesn’t need additional storage overhead, making your 351-day storage need 1.158 PiB. You can support this with 58 UltraWarm1.large.search instances. The following table gives the total cost for this deployment, with 3-year AURIs for the hot tier. The or1 instances’ Amazon S3 cost is rolled into the S3 column.
| . | Hot | UltraWarm | S3 | Total |
| im4gn.16xlarge.search | $220,278 | $1,361,654 | $333,590 | $1,915,523 |
| or1.16xlarge.search | $337,696 | $1,361,654 | $418,136 | $2,117,487 |
| r6g.12xlarge.search | $270,410 | $1,361,654 | $333,590 | $1,965,655 |
You can further reduce the cost by moving data to UltraWarm cold storage. Cold storage reduces cost by reducing availability of the data—to query the data, you must issue an API call to reattach the target indexes to the UltraWarm tier. A typical pattern for 1 year of data keeps 14 days hot, 76 days in UltraWarm, and 275 days in cold storage. Following this pattern, you use 6 hot nodes and 13 UltraWarm1.large.search nodes. The following table illustrates the cost to run Fizzywig’s 3 TB daily workload. The or1 cost for Amazon S3 usage is rolled into the UltraWarm nodes + S3 column.
| . | Hot | UltraWarm nodes + S3 | Cold | Total |
| im4gn.16xlarge.search | $220,278 | $377,429 | $261,360 | $859,067 |
| or1.16xlarge.search | $337,696 | $461,975 | $261,360 | $1,061,031 |
| r6g.12xlarge.search | $270,410 | $377,429 | $261,360 | $909,199 |
By employing Amazon S3 backed storage options, you’re able to reduce cost even further, with a single-copy or1 deployment at $337,000, and a maximum of $1 million annually with or1 instances.
OpenSearch Service zero-ETL for Amazon S3
When you use OpenSearch Service zero-ETL for Amazon S3, you keep all your secondary and older data in Amazon S3. Secondary data is the higher-volume data that has lower value for direct inspection, such as VPC Flow Logs and WAF logs. For these deployments, you keep the majority of infrequently queried data in Amazon S3, and only the most recent data in your hot tier. In some cases, you sample your secondary data, keeping a percentage in the hot tier as well. Fizzywig decides that they want to have 7 days of all of their data in the hot tier. They will access the rest with direct query (DQ).
When you use direct query, you can store your data in JSON, Parquet, and CSV formats. Parquet format is optimal for direct query and provides about 75% compression on the data. Fizzywig is using Amazon OpenSearch Ingestion, which can write Parquet format data directly to Amazon S3. Their 3 TB of daily source data compresses to 750 GB of daily Parquet data. OpenSearch Service maintains a pool of compute units for direct query. You are billed hourly for these OpenSearch Compute Units (OCUs), scaling based on the amount of data you access. For this conversation, we assume that Fizzywig will have some debugging sessions and run 50 queries daily over one day worth of data (750 GB). The following table summarizes the annual cost to run Fizzywig’s 3 TB daily workload, 7 days hot, 358 days in Amazon S3.
| . | Hot | DQ Cost | OR1 S3 | Raw Data S3 | Total |
| im4gn.16xlarge.search | $220,278 | $2,195 | $0 | $65,772 | $288,245 |
| or1.16xlarge.search | $337,696 | $2,195 | $84,546 | $65,772 | $490,209 |
| r6g.12xlarge.search | $270,410 | $2,195 | $0 | $65,772 | $338,377 |
That’s quite a journey! Fizzywig’s cost for logging has come down from as high as $14 million annually to as low as $288,000 annually using direct query with zero-ETL from Amazon S3. That’s a savings of 4,800%!
Sampling and compression
In this post, we have looked at one data footprint to let you focus on data size, and the trade-offs you can make depending on how you want to access that data. OpenSearch has additional features that can further change the economics by reducing the amount of data you store.
For logs workloads, you can employ OpenSearch Ingestion sampling to reduce the size of data you send to OpenSearch Service. Sampling is appropriate when your data as a whole has statistical characteristics where a part can be representative of the whole. For example, if you’re running an observability workload, you can often send as little as 10% of your data to get a representative sampling of the traces of request handling in your system.
You can further employ a compression algorithm for your workloads. OpenSearch Service recently released support for Zstandard (zstd) compression that can bring higher compression rates and lower decompression latencies as compared to the default, best compression.
Conclusion
With OpenSearch Service, Fizzywig was able to balance cost, latency, throughput, durability and availability, data retention, and preferred access patterns. They were able to save 4,800% for their logging solution, and management was thrilled.
Across the board, im4gn comes out with the lowest absolute dollar amounts. However, there are a couple of caveats. First, or1 instances can provide higher throughput, especially for write-intensive workloads. This may mean additional savings through reduced need for compute. Additionally, with or1’s added durability, you can maintain availability and durability with lower replication, and therefore lower cost. Another factor to consider is RAM; the r6g instances provide additional RAM, which speeds up queries for lower latency. When coupled with UltraWarm, and with different hot/warm/cold ratios, r6g instances can also be an excellent choice.
Do you have a high-volume, logging workload? Have you benefitted from some or all of these methods? Let us know!
About the Author
Jon Handler is a Senior Principal Solutions Architect at Amazon Web Services based in Palo Alto, CA. Jon works closely with OpenSearch and Amazon OpenSearch Service, providing help and guidance to a broad range of customers who have vector, search, and log analytics workloads that they want to move to the AWS Cloud. Prior to joining AWS, Jon’s career as a software developer included 4 years of coding a large-scale, ecommerce search engine. Jon holds a Bachelor’s of the Arts from the University of Pennsylvania, and a Master’s of Science and a PhD in Computer Science and Artificial Intelligence from Northwestern University.
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