Caching is a technique used to store data in temporary storage for quick access. This approach tends to reduce latency and improves the performance of applications by providing data closer to the users. In this context, we will discuss caching strategies and services, with particular emphasis on Amazon ElastiCache as it relates to the AWS Certified Solutions Architect – Associate (SAA-C03) exam.
Caching strategies
Here are some common caching strategies:
- Cache-aside (a.k.a Lazy-loading): This strategy fetches the data on demand. If an application requests data that is not present in the cache, it will load the data from the backing store. After the data is loaded, it will be added to the cache. For subsequent requests, the data will be served from the cache.
- Read-through: In this strategy, the application reads data through the cache. If the data is not found in the cache, it fetches the data from the backing store, caches it and then returns it to the application.
- Write-through: Here, the application writes data through the cache. The cache writes or updates the data in the backing store and also updates the data in the cache.
- Write-behind (a.k.a Write-back): In this strategy, whenever data is written, the cache is updated immediately while the write to the backing store is scheduled for a later time. This improves the write performance of the application.
- Refresh-ahead: This caching strategy preloads the data to the cache prior to its expiration. This approach realizes its advantage when you know in advance that certain data will be requested in near future.
Amazon ElastiCache
Amazon ElastiCache is a fully managed, in-memory data store and cache service by Amazon Web Services (AWS). ElastiCache works with both the Redis and Memcached engines, making it simpler to set up, run, and scale popular open-source compatible in-memory data stores.
ElastiCache provides the following benefits:
- Ease of setup, operation, and scaling: As a fully managed service, it allows you to easily deploy, run, and scale popular open-source compatible in-memory data stores in the cloud.
- Improved application performance: By retrieving from an in-memory system, instead of disk-based databases, apps experience drastically reduced latency, making them faster.
- Cost-effective: ElastiCache saves costs as it reduces the workloads on databases. Moreover, it allows for choosing instances that are the most cost-effective for your workload.
Here’s a sample command to create a Memcached cluster using AWS CLI:
bash
aws elasticache create-cache-cluster \
--cache-cluster-id my-memcached-cluster \
--engine memcached \
--cache-node-type cache.r5.large \
--num-cache-nodes 5 \
--region us-west-2
This command creates a cluster called “my-memcached-cluster” using Memcached, 5 nodes of type “cache.r5.large”, and in the “us-west-2” region.
Conclusion
Caching is an efficient strategy to improve performance and reduce the latency of applications. Amazon ElastiCache is a promising solution that simplifies the setup, operation, and scaling for in-memory cache in the cloud. As an aspiring AWS Certified Solutions Architect, understanding these caching strategies, services, and getting hands-on experience with them is vital.
Practice Test
True or False: Amazon ElastiCache supports only in-memory caching.
- True
- False
Answer: False
Explanation: ElastiCache supports both in-memory and disk-based caching. It supports two different caching engines: Memcached and Redis.
Which of the following caching strategies refers to the removal of rarely used items when the cache is full?
- A. LRU (Least Recently Used)
- B. MRU (Most Recently Used)
- C. FIFO (First In, First Out)
- D. LIFO (Last In, First Out)
Answer: A. LRU (Least Recently Used)
Explanation: LRU strategy involves removing the least recently used items first. This strategy is beneficial for retaining frequently accessed items in the cache.
True or False: Amazon ElastiCache data is durable and persistent.
- True
- False
Answer: False
Explanation: As an in-memory caching system, ElastiCache is not a durable or persistent data storage system. The data in ElastiCache is stored in volatile memory and is lost in case of component failure.
What is the recommended method to secure your Amazon ElastiCache environment?
- A. Enable AWS CloudTrail
- B. Use IAM roles
- C. Use Security Groups
- D. Use AWS Shield
Answer: C. Use Security Groups
Explanation: You can control access to your ElastiCache environment by using AWS security groups, which act as a firewall to control network access.
Which of the following is NOT a feature of Amazon ElastiCache?
- A. Automatic partitioning
- B. Data replication
- C. Backup and restore
- D. Isolation of cache environments
Answer: A. Automatic partitioning
Explanation: ElastiCache does not provide automatic partitioning. It does provide data replication, backup and restore and isolation of cache environments.
True or False: In Amazon ElastiCache, you can enable encryption in transit for all current generation Memcached nodes.
- True
- False
Answer: False
Explanation: Encryption in transit is only supported for Redis nodes and not for Memcached nodes.
Which of the following AWS services can be used with Amazon ElastiCache to provide a seamless scaling and load balancing?
- A. Amazon RDS
- B. Amazon S3
- C. Amazon EC2
- D. Amazon VPC
Answer: C. Amazon EC2
Explanation: Amazon EC2 instances can be used in combination with ElastiCache to handle the client load and maintain high availability.
True or False: Amazon ElastiCache only supports horizontal scaling.
- True
- False
Answer: False
Explanation: ElastiCache supports both horizontal scaling (adding more nodes) and vertical scaling (adding more computational resources to existing nodes).
Which Amazon ElastiCache engine supports the use of replication to provide higher availability and read scalability?
- A. Memcached
- B. Redis
Answer: B. Redis
Explanation: Redis supports replication by creating one or more read replica nodes, which can provide higher read scalability and availability.
True or False: It is possible to have Multi-AZ with automatic failover enabled with Amazon ElastiCache using Memcached.
- True
- False
Answer: False
Explanation: Multi-AZ with automatic failover is only supported for Redis. Memcached does not support this feature.
Interview Questions
What is Amazon ElastiCache and what is it used for?
Amazon ElastiCache is used for deploying, operating, and scaling an in-memory cache in the cloud. It helps improve the performance of web applications by leveraging cached data rather than relying entirely on slower disk-based databases.
For which types of applications is Amazon ElastiCache particularly useful?
Amazon ElastiCache is especially beneficial for workloads that require very low latency, high throughput, and are read-heavy or have a high degree of data redundancy. This can include social networking, gaming, media sharing and Q&A portals.
What is the advantage of using Amazon ElastiCache over setting up your own caching system?
Amazon ElastiCache allows you to effortlessly set up, maintain, and scale distributed in-memory cache environments in the cloud. It provides a high-performance, resizable, and cost-effective in-memory cache, while removing the complexity associated with deploying and managing a distributed cache environment.
What are the two caching strategies used in Amazon ElastiCache?
There are two common caching strategies used in ElastiCache: Lazy Loading and Write Through. Lazy Loading only adds data to the cache when necessary, avoiding cache fill up with unused data, while Write Through adds data to the cache whenever there’s a change to the database, ensuring that the cache is always up-to-date.
What happens when an Amazon ElastiCache node fails?
When an ElastiCache node fails, it is automatically detected and replaced by the service. The self-healing feature of ElastiCache ensures high availability and durability of data.
Can you use Amazon ElastiCache with other AWS services?
Yes, Amazon ElastiCache can be integrated with other AWS services such as Amazon RDS, Amazon DynamoDB, and AWS Lambda for efficient data processing and workflows.
Is there built-in support for partitioning in ElastiCache?
Yes, ElastiCache supports partitioning with Redis Cluster, which provides the ability to automatically split your data across multiple shards.
Does ElastiCache support secure data encryption?
Yes. Amazon ElastiCache for Redis gives you the ability to easily scale for higher levels of data security by running workloads in an Amazon VPC setting and using VPC security groups to control network access to your clusters.
How does data sharding work in ElastiCache for Redis?
Data sharding in ElastiCache for Redis works by allowing you to partition your data across multiple nodes. This allows you to add more capacity, while ensuring that your application remains highly available.
What are the benefits of using the ElastiCache Multi-AZ feature?
The Multi-AZ feature in Amazon ElastiCache automatically creates and maintains a standby replica of your primary in a separate Availability Zone. In case of a failure, it promotes the replica to become primary with almost no delay in replication, ensuring high availability.
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