Redis vs ElastiCache: Which Is More Cost Effective?

The biggest ElastiCache cost driver is easy to miss: you never get the full node memory as usable keyspace. By default AWS documents that 25% of memory is reserved for operations like backups and replication and is unusable, so the actual capacity available to customers is smaller than the instance specifications suggest.

This matters because memory is what you pay for. If you size on the specs and not the usable keyspace, you have a choice: evict more data, deal with out-of-memory errors, or grow your ElastiCache bill with more shards, more replicas, or a migration to a larger node. We designed Redis Cloud so you get the dataset size you want without managing node-level overhead.

This post explains Redis vs ElastiCache cost with concrete node examples, how overhead and scaling affect TCO, and what ElastiCache’s move to Valkey means for long-term cost and innovation.

How much keyspace do you really get on ElastiCache?

AWS requires a minimum 25% reserve for either Valkey or Redis OSS. The reserve is also higher on small nodes (30%) and micro nodes (50%). For auto-tiering nodes, the recommendation is also 50%. And if you’re using BGSAVE to snapshot your data, the ElastiCache User Guide recommends doubling the memory requirements! The result: usable keyspace is 75% at most of the listed node memory and 50% if you require data durability.

Examples from the AWS pricing page:

* - Burstable t-class nodes also have baseline CPU and network limits, and burst is best-effort and can induce costs.

Replication requirements and HA

High availability requires replicas, but the number you need differs by platform.

• ElastiCache: The ElastiCache SLA specifically excludes downtime that results from not following their recommended best practices. These best practices require “two or more replicas across Availability Zones.” This increases the cost of memory and nodes that are provisioned for an HA dataset by three times.
• Redis Cloud: We meet our HA SLA with two copies (one primary and one replica). This cuts the capacity requirement to 2x while also reducing operational complexity.

When combined with the memory overhead needed for ElastiCache, you can start to see how much resource inefficiency you can accumulate. For an HA 100 GB dataset:

• ElastiCache sizing = 100 GB × 4/3 overhead × 3 copies ≈ 400 GB provisioned
• Redis Cloud sizing = 100 GB × 2 copies = 200 GB provisioned

This replication difference compounds the memory overhead gap and is a major driver of higher ElastiCache TCO.

Why this inflates real costs

Sizing on headline memory and HA minimums leads to underprovisioning. You add shards, replicas, or larger nodes later, which raises spend and adds work.

We see the impact most in two places:

• Scaling up. Moving from smaller nodes to larger nodes is a migration requiring a maintenance window and/or downtime. Client changes and rebalancing add effort and risk.
• Scaling out. Adding more shards also adds to costs and can result in a maintenance window or downtime if the instance is running hot.

Environment-level economics vs sticker price

Comparisons are fair when you account for overhead and HA replicas. But also look at the whole deployment instead of a single node.

In a 250 GB dataset example sized for throughput and HA, ElastiCache on r7g.xlarge or m7g.8xlarge looks materially more expensive once the 25% reserve and additional replicas are applied, while we at Redis deliver the target dataset size directly.

Multi-tenancy compounds the effect. Redis can place many small databases on shared cluster infrastructure. This increases small node efficiency, lowers overall TCO and also provides consistent performance for smaller datasets that can be problematic in ElastiCache.

Reserved nodes and flexibility

Reserved nodes reduce ElastiCache hourly rates, but discounts are tied to a node family and region. AWS added size flexibility within a family in October 2024, which helps, but you’re still constrained to that family and region for the term. We take a different approach at Redis. We discount across a pool of credits and don’t force you into a particular node type, region, or memory size.

Redis vs. ElastiCache cost: Where Redis reduces your cost and risk

• We sell usable dataset, not headline memory. You don’t need to calculate reserves, replicas, or durability overhead.
• Multi-tenancy. Pack many databases into shared underlying infrastructure to avoid underutilized memory and CPUs.
• Feature set that replaces extra systems. Redis Query Engine and Redis Data Integration are two Redis Cloud-only features that reduce usage of separate services and movement of data.

The Valkey factor

ElastiCache now runs on Valkey, and AWS has added a Valkey-specific discount to encourage adoption. This lowers the apparent gap in hourly pricing when compared to Redis Cloud, so the services can look closer on cost. However, this needs to be weighed against the memory overhead, replication requirements, and feature limitations discussed above.

The bigger concern may be that offering Valkey at a lower price doesn’t address all of the issues:

• Valkey diverges from Redis and lacks our roadmap and innovation.
• ElastiCache for Valkey misses features that cut operational cost, including Redis Data Integration, Redis Query Engine, and Redis Flex.
• Customers tied to Valkey risk future migration work when Redis-only capabilities become critical.

So while the discount changes the sticker price, the underlying TCO gap may remain once you factor in missing features, scaling complexity, and lock-in.

ElastiCache’s headline price doesn’t reflect what you get. The 25% reserve, write-heavy headroom, replicas, and node limits turn a simple estimate into a larger bill. We focus you on usable dataset, pack small workloads efficiently, and remove re-sharding and migration work.

If you care about predictable cost and steady access to new capabilities, choose Redis. See more comparisons at redis.io/compare/elasticache.

If ElastiCache costs are creeping up, we’ll review your setup and show where Redis cuts spend. Book a meeting with our team and see how much you can save.