ElastiCache in AWS: What It Is and How It Works

Introduction

In the world of modern applications, speed and responsiveness are non-negotiable. Whether it's serving millions of user requests, powering real-time analytics, or managing high-frequency transactions, traditional databases sometimes struggle to keep up with the demands of low-latency performance. This is where in-memory databases step in, offering lightning-fast access to data by storing it in memory rather than on disk. They are ideal for scenarios like caching, session storage, or even real-time leaderboard calculations.

In this blog, we’ll explore what Amazon ElastiCache is, how it works, and why it’s a go-to choice for businesses aiming to deliver fast, reliable, and scalable applications.

What is Amazon ElastiCache ?

Amazon ElastiCache is a managed service designed to make it easy to set up, operate, and scale in-memory data stores or caching environments in the cloud. By removing the complexity of deploying and managing a distributed cache, ElastiCache provides a high-performance, scalable, and cost-effective solution to boost application speed and efficiency.

ElastiCache supports two operational modes: a serverless cache for seamless scalability or a more customized cache cluster for specific requirements.

Amazon ElastiCache Engine Types

Amazon ElastiCache supports three cache engines: Memcached, Redis OSS, and the recently introduced Valkey. Each engine is designed for specific use cases, offering unique features and benefits:

Amazon ElastiCache for Memcached

Memcached is a simple yet powerful in-memory key-value store, ideal for use cases that require fast, lightweight caching. While it doesn’t offer the advanced data structures or extensive feature set of Redis or Valkey, Memcached is designed to handle straightforward caching needs with minimal complexity, making it an excellent choice for developers looking for performance and scalability without overhead.

Key Features of Memcached:

• Lightweight and Straightforward: A simple, no-frills caching solution optimized for high-speed storage and retrieval of data.
• Scalability: Easily scale out or in by adding or removing nodes to meet changing workload demands.
• Multi-Threaded Architecture: Supports multiple threads for high-performance workloads, allowing efficient utilization of modern hardware.
• Ease of Use: Its simplicity and minimal configuration make it accessible for developers without extensive caching expertise.
• In-Transit Encryption: Offers secure communication to protect data as it moves between nodes and clients.

Amazon ElastiCache For Redis

Redis OSS has long been a trusted in-memory data structure store, known for its high performance, robust features, and extensive adoption across industries. It is commonly used as a database, cache, and message broker. With support for various data structures like strings, hashes, lists, and sorted sets, Redis is highly versatile and suitable for a wide range of applications, from caching to real-time analytics.

Key Features of Redis OSS:

• Advanced Data Structures: Includes hashes, sorted sets, and streams for versatile use cases.
• High Availability: Supports automatic failover for enhanced reliability.
• Encryption: Offers encryption both in-transit and at-rest.
• Clustering and Sharding: Enables scalability for workloads of varying sizes.
• Ease of Use: Widely recognized for its straightforward setup and integration with modern applications.

However, Redis has transitioned to a source-available license, raising concerns about its long-term availability as a fully open-source solution. It remains commercially supported by Redis Inc., which offers enterprise-level enhancements and services.

Amazon ElastiCache For Valkey

In October 2024, AWS announced support for Valkey in ElastiCache, introducing it as a cost-effective, fully open-source alternative to Redis OSS. Developed as an open-source fork of Redis OSS in response to licensing changes by Redis Inc., Valkey is designed to be a drop-in replacement that retains Redis's core functionality while offering community-driven enhancements. Backed by major technology companies, including AWS, Valkey benefits from robust development and support.

Key Advantages of Valkey:

• Cost Efficiency: ElastiCache for Valkey offers serverless pricing that is 33% lower and node-based pricing that is 20% lower compared to Redis OSS, making it a highly cost-effective option.
• Enhanced Performance: Features multi-threaded architecture and improved scalability, offering:
  • Automatic cluster failover.
  • Per-slot metrics for detailed monitoring and performance insights.
• Rich Data Support: Includes geospatial data, hyperloglogs, streams, and more.
• Open Source: Governed under the BSD 3-clause license, ensuring it remains community-driven and freely available.
• Memory Efficiency: Utilizes a new dictionary structure for reduced memory overhead and supports experimental RDMA for high-performance environments.
• Developer-Friendly: Compatible with major programming languages and over 100 open-source clients.

Key Differences Between Redis and Valkey

Redis and Valkey are two in-memory data structure stores that share significant similarities, making them a natural choice for comparison. Both are designed to handle complex data structures, provide exceptional performance, and cater to advanced caching and database use cases. Unlike Memcached, which is a lightweight and simple key-value store, Redis and Valkey offer richer functionality, making it more relevant to compare these two engines.

• Licensing: Redis has transitioned to a source-available license, raising concerns about its long-term open-source availability. In contrast, Valkey remains fully open-source under the BSD 3-clause license, ensuring community-driven development and flexibility.
• Performance: Valkey significantly enhances performance with the introduction of multi-threading in Valkey 8.0, along with improved memory efficiency. These advancements enable Valkey to achieve up to 230% higher throughput and 70% lower latency compared to earlier versions. In contrast, Redis, while highly performant, continues to rely on a single-threaded architecture for most operations, which can limit its scalability in certain scenarios.
• Monitoring: Valkey offers detailed per-slot metrics for advanced observability, giving developers deeper insights into performance and usage. Redis provides basic monitoring tools, which may suffice for simpler workloads but lack the granularity of Valkey.
• Scalability: Valkey enhances scalability with improved failover mechanisms and seamless operation in distributed environments. Redis, while robust, continues to rely on its well-established clustering and sharding capabilities.
• Community Support: Redis is commercially supported by Redis Inc., which drives its development and enterprise offerings. Valkey, on the other hand, is governed by a global community and backed by major technology companies, including AWS, Google Cloud, and Oracle, ensuring a strong development roadmap.

How ElastiCache Works ?

Amazon ElastiCache Serverless

ElastiCache Serverless provides a simplified caching experience, allowing you to set up and manage a cache without worrying about capacity planning, hardware management, or cluster design. All you need to do is provide a name for your cache, and ElastiCache Serverless will give you a single endpoint to configure with your Valkey, Redis OSS, or Memcached client, enabling seamless access.

Key Benefits of ElastiCache Serverless

1. No Capacity Planning:
   • Automatically adjusts memory, compute, and network resources to meet your application’s needs.
   • Scales both vertically (increasing node size) and horizontally (adding nodes) to handle changes in workload seamlessly.
2. Pay-As-You-Go:
   • You pay only for the data stored and the compute resources utilized by your workload, keeping costs aligned with usage.
3. High Availability:
   • Data is automatically replicated across multiple Availability Zones (AZs) for reliability.
   • Failed nodes are replaced automatically, ensuring minimal downtime.
   • Offers a 99.99% availability SLA, guaranteeing robust performance.
4. Automatic Software Upgrades:
   • Automatically applies minor updates and patches with no impact on availability.
   • Sends notifications for major version upgrades, giving you control over scheduling updates.
5. Security:
   • Data is encrypted both in transit and at rest.
   • Choose between an AWS-managed encryption key or your own Customer Managed Key for added security.

The following diagram illustrates how ElastiCache Serverless works.

How It Works

1. Virtual Private Cloud (VPC) Endpoint:
   • When you create a serverless cache, ElastiCache sets up a VPC Endpoint in the subnets of your choice within your VPC.
   • Your application connects to the cache via this endpoint.
2. Simplified Endpoint:
   • A single DNS endpoint connects your application to the cache.
   • ElastiCache Serverless uses a proxy layer to manage connections, reducing client-side complexity.
   • The proxy layer handles cluster topology changes transparently, so your application doesn’t need to rediscover nodes when the cluster scales or updates.
3. Proxy Layer Operations:
   • Requests from your application are routed through a network load balancer to the proxy layer.
   • The proxy layer balances requests across cache nodes, ensuring efficient resource utilization.
   • It manages scaling, node replacements, and software updates without interrupting your application or requiring connection resets.

This streamlined approach ensures high performance, scalability, and simplicity, making ElastiCache Serverless an excellent choice for dynamic workloads.

Self-Designed Clusters

For users who need finer control over their caching environment, Self-Designed ElastiCache Clusters allow you to customize your setup based on workload requirements. You can choose the cache node family, size, and the number of nodes to create a cluster tailored to your specific use case. This option supports both Valkey, Redis OSS, and Memcached, offering flexibility for advanced configurations.

Key Benefits of Self-Designed Clusters

1. Custom Cluster Design:
   • Choose the number of shards and nodes (primary and replicas) in each shard.
   • Deploy clusters in a single Availability Zone (AZ) for low latency or across multiple AZs for high availability.
   • Operate Valkey or Redis OSS in either cluster mode (with multiple shards) or non-cluster mode (with a single shard).
2. Fine-Grained Control:
   • Customize cache engine settings with Valkey, Redis OSS, or Memcached-specific parameters.
   • Configure specific operational details to optimize performance for your workload.
3. Manual and Automatic Scaling:
   • Vertical Scaling: Adjust node sizes manually to handle larger workloads.
   • Horizontal Scaling: Add new shards or replicas to expand capacity.
   • Auto-Scaling: Configure automatic scaling based on CPU, memory usage, or predefined schedules, enabling efficient resource utilization.

The following diagram illustrates how ElastiCache Self-Designed Clusters work.

How It Works

With a self-designed cluster, you have complete control over where and how your cache nodes are deployed:

1. Node Placement:
   • Nodes can be deployed in a single AZ for lower latency or distributed across multiple AZs to ensure high availability.
2. Cluster Mode Options:
   • Operate in cluster mode for larger, distributed caches with multiple shards.
   • Use non-cluster mode for simpler setups with a single shard.
3. Scaling Flexibility:
   • Manually increase or decrease node size based on workload needs.
   • Add or remove shards or replicas to expand or optimize the cluster's capacity.
   • Enable Auto-Scaling to handle workload spikes automatically, minimizing manual intervention.

Key Considerations for ElastiCache: Pricing, Data Storage, and Backups

When deploying Amazon ElastiCache, you can choose between Serverless and Self-Designed Clusters, with distinct pricing models and resource utilization metrics. Here is some information to keep in mind when choosing between serverless and self-designed clusters.

Pricing Dimensions

1. Serverless:
   • Data Storage: Billed in GB-hours, based on the hourly average of data stored in the cache, with a minimum of 1 GB.
   • ElastiCache Processing Units (ECPUs): Measures vCPU time and data transferred for commands. For example:
     • Simple commands (e.g., GET/SET up to 1 KB) consume 1 ECPU per KB transferred.
     • More complex commands (e.g., HMGET with Valkey/Redis OSS or multiget with Memcached) consume ECPUs proportional to the vCPU time or data transferred.
   • Use the ElastiCacheProcessingUnits metric to monitor ECPU usage.
2. Self-Designed Clusters:
   • Node Hours: Charged hourly for each cache node, depending on the chosen EC2 node family, size, and number of nodes.

Backups

• Both Serverless and Self-Designed Clusters support manual and automatic backups.
• Backups store all cache data and metadata, enabling restoration to an existing cache or seeding a new one.

Amazon ElastiCache Pricing

ElastiCache operates on a pay-as-you-go model, allowing you to pay only for the capacity you use without upfront costs or long-term commitments. For predictable workloads, there’s also an option to save costs with reserved instances.

Key Factors Affecting Pricing

1. Node Type and Usage:
   • For self-designed clusters, nodes are EC2 instances running custom ElastiCache software, and charges are based on the number, type, and usage of nodes.
2. Serverless Pricing:
   • With ElastiCache Serverless, costs are based on:
     • Data Storage: Billed in gigabyte-hours (GB-hrs), calculated by monitoring and averaging the amount of data stored.
     • ElastiCache Processing Units (ECPUs): Measures the vCPU time and data transferred during operations. For example, a simple GET request transferring 1 KB of data consumes 1 ECPU, while larger or more complex commands consume proportionally more.
3. Reserved Instances:
   • Reserved pricing lets you make an upfront payment to secure a one- or three-year term at a significantly discounted hourly rate.
4. Data Tiering:
   • Available for ElastiCache for Redis and Valkey, data tiering moves less frequently used data to SSDs, optimizing costs while increasing storage capacity.
5. Backup Storage:
   • You can store backups at a rate of $0.085 per GiB per month for all AWS Regions. There are no data transfer fees for creating a backup or for restoring data from a backup to a cache.
6. Data Transfers:
   • Data transfers within the same Availability Zone are free.
   • Transfers across AZs in the same region cost $0.01/GB, while cross-region replication incurs extra charges.
7. Pricing Models:
   • On-Demand: Flexible, hourly billing for workloads with unpredictable usage.
   • Reserved Instances: Offers substantial discounts for consistent, long-term use.

For a more detailed explanation of ElastiCache pricing, including examples, check out our ElastiCache Pricing Breakdown blog

Amazon MemoryDB  vs Amazon ElastiCache

At first glance, Amazon ElastiCache and Amazon MemoryDB may seem similar, as both leverage in-memory technology for ultra-fast performance and support popular caching engines like Valkey and Redis OSS. However, their purposes are distinct, and understanding these differences is crucial for choosing the right solution for your workload.

Amazon ElastiCache

ElastiCache is primarily a caching service, designed to accelerate data access by serving as an in-memory layer for your existing primary database or data store. It supports Valkey, Redis OSS, and Memcached, making it highly versatile.

Key Use Cases for ElastiCache:

• Caching Layer: Enhances performance by storing frequently accessed data in memory, reducing the load on your database.
• Cost Optimization: Saves on database costs by handling high-read throughput workloads in the cache rather than scaling the underlying database.
• Valkey and Redis OSS APIs: Supports data structures and APIs for accessing cached data stored in a primary database or data store.

When to Choose ElastiCache:

• When you need microsecond performance for read/write operations.
• When you want to offload heavy database read/write loads without replacing your existing database.
• When caching frequently accessed data is your primary goal.

Amazon MemoryDB

MemoryDB is a durable, in-memory database, designed to act as the primary database for workloads requiring both persistence and ultra-fast performance. It is compatible with Valkey and Redis OSS and combines in-memory speed with persistent data storage.

Key Use Cases for MemoryDB:

• Primary Database: Offers microsecond read and single-digit millisecond write latency with full durability, making it suitable for workloads where persistence is critical.
• Simplified Architecture: Combines the functionality of a database and cache, eliminating the need for separate solutions.
• Valkey and Redis OSS APIs: Enables building applications using Valkey or Redis OSS APIs while ensuring data durability.

When to Choose MemoryDB:

• When you need a durable primary database that offers in-memory performance.
• When you want to streamline your architecture by combining database and caching into one system.
• When your workload requires persistently stored data with high-speed access.

Conclusion

Amazon ElastiCache stands as a versatile and high-performance solution for businesses looking to optimize data access speeds and scalability. Whether you choose the simplicity of Serverless or the control of Self-Designed Clusters, ElastiCache provides flexibility to meet diverse workload requirements. With support for powerful engines like Redis OSS, Valkey, and Memcached, ElastiCache ensures seamless integration, robust performance, and cost efficiency.

For users seeking durability alongside speed, Amazon MemoryDB complements ElastiCache by serving as a durable in-memory primary database, providing an alternative for workloads requiring persistent data storage.

By leveraging the right configuration—be it caching for rapid data retrieval or a durable in-memory database—you can optimize your applications for responsiveness, scalability, and cost-effectiveness. For a deeper dive into pricing details and cost-saving strategies, explore our blog on ElastiCache Pricing Breakdown.

Whether your focus is on real-time analytics, caching, or session storage, Amazon ElastiCache offers the tools and flexibility to elevate your application performance in today’s fast-paced digital landscape.