Caching

Caching is a method used to store copies of frequently accessed data. The main aim of caching is to enhance the speed and performance of data retrieval. This process reduces the load on the primary data source and accelerates the speed at which the data is delivered to the user.

Caching Services in AWS

AWS offers two primary services for caching: Amazon ElasticCache and Amazon CloudFront.

Amazon ElasticCache

ElasticCache is a web service that makes it easy to deploy, operate, and scale an in-memory cache in the cloud. The service improves the performance of web applications by storing critical pieces of data in memory for low-latency access. ElasticCache supports two open-source caching engines: Memcached and Redis.

• Memcached: It is a general-purpose distributed memory caching system that is easy to use. It is a good choice for simplifying the design of scaling an existing database-driven application.
• Redis: Besides being a caching tool, it is also used as a database. Redis supports a broader range of data structures like lists, sets, and sorted sets.

Amazon CloudFront

CloudFront is a fast content delivery network (CDN) service that securely delivers data, videos, applications, and APIs to customers globally with low latency, high transfer speeds within a developer-friendly environment. CloudFront can be used to cache static content (images, stylesheets, JavaScript, etc.) and dynamic content (loading data from a database).

Implementing Caching in AWS

For a practical understanding, let’s consider an example application where caching is implemented using ElasticCache.

Step 1: Create an ElasticCache Cluster from the AWS Management Console.

Step 2: In your application, configure the connection to the ElasticCache cluster using the endpoint provided by AWS.

const client = require(‘redis’).createClient({
host: ‘myelasticcachecluster.eaorzf.ng.0001.usw2.cache.amazonaws.com’,
port: 6379
});

Step 3: In your application, use the client object to store and retrieve data from the cache.

// Storing data
client.set(‘key’, ‘value’, (err) => {
if (err) throw err;
console.log(‘Value stored in cache’);
});

// Retrieving data
client.get(‘key’, (err, result) => {
if (err) throw err;
console.log(‘Value from cache:’, result);
});

Importance of Caching in AWS

Caching plays a pivotal role when building applications in AWS:

1. Increased Performance: Caching enhances the speed of your applications by storing frequently accessed data in a cache, reducing the time taken to fetch data from the main storage area.
2. Reduced Costs: The use of caching can help to decrease the read traffic on your primary database, and therefore reducing overall operation costs.
3. Scalability: Caching allows your application to scale while ensuring that the system continues to provide low-latency access to your frequently accessed data.

It’s vital, as a developer, to understand where and when to implement caching in your AWS environment. Knowing the appropriate service to implement, and the beneficial impacts caching can provide, is key to your success not only in AWS but also in the AWS Certified Developer – Associate (DVA-C02) exam.

Practice Test

When the performance of an application is improved by caching data, it is referred to as ‘Write Through Caching’. (True/False)

• True
• False

Answer: False.

Explanation: This is not ‘Write Through Caching’. Instead, it is usually done in ‘Read Through Caching’.

What is the maximum size of a single item that can be cached in Amazon ElastiCache for Redis?

• A) 128 KB
• B) 256 KB
• C) 512 MB
• D) 1 GB

Answer: C) 512 MB.

Explanation: Amazon ElastiCache for Redis supports up to 512 MB for a single cached item.

Which AWS service is designed specifically for caching data and speeding up applications by enabling you to retrieve information from fast, in-memory systems, instead of slower disk-based systems?

• A) Amazon EC2
• B) Amazon S3
• C) Amazon ElastiCache
• D) Amazon RDS

Answer: C) Amazon ElastiCache.

Explanation: Amazon ElastiCache is a web service that makes it easy to deploy, operate, and scale an in-memory data store or cache in the cloud.

In AWS ElastiCache, ‘Write Through Caching’ ensures that data modifications are written to cache as well as the underlying permanent storage. (True/False)

• True
• False

Answer: True.

Explanation: In ‘Write Through Caching’ the data intended to be written is stored to the cache and the corresponding database at the same time.

When using caching in AWS, data is visible to the application immediately after cache invalidation. (True/False)

• True
• False

Answer: True.

Explanation: After cache invalidation, the data is completely removed from cache storage and will be fetched again from the original storage when accessed next time.

Select the caching strategies available in AWS.

• A) Write Around Caching
• B) Read Through Caching
• C) Write Through Caching
• D) Cache on Demand

Answer: B) Read Through Caching and C) Write Through Caching.

Explanation: AWS supports the ‘Read Through Caching’ and ‘Write Through Caching’. The others mentioned are not specific caching strategies used in AWS.

Cached data in Amazon ElastiCache is automatically encrypted at rest. (True/False)

• True
• False

Answer: False.

Explanation: Data encryption at rest must be enabled manually when creating a new ElastiCache for Redis cluster with the “Encryption At-Rest” checkbox.

The primary purpose of caching is to increase data persistency.

• A) True
• B) False

Answer: B) False.

Explanation: The primary purpose of caching is to increase data retrieval performance by reducing the need to access the underlying slower storage layer.

Amazon CloudFront is a content delivery network (CDN) offered by AWS which uses caching mechanisms.

• A) True
• B) False

Answer: A) True

Explanation: Amazon CloudFront is a fast content delivery network (CDN) service that securely delivers data, videos, applications, and APIs to customers globally, it uses edge location caching to improve speed of delivery.

An ElastiCache cluster can span across multiple regions. (True/False)

• True
• False

Answer: False

Explanation: Each cluster operates in a single AWS region and cannot span multiple regions. However, you can replicate a snapshot to another region and create a new cluster from the snapshot.

Which caching type in Amazon ElastiCache is best suited for relatively small and not frequently changing data set such as configuration settings?

• A) Memcached
• B) Redis

Answer: A) Memcached

Explanation: Memcached is designed for simplicity and handling small and relatively static data, such as HTML code fragments, strings, and numbers.

In AWS ElastiCache, horizontal partitioning is implemented using the sharding methodology. (True/False)

• True
• False

Answer: True

Explanation: In AWS ElastiCache for Redis, horizontal partitioning is implemented using the sharding methodology, which allows it to split and replicate large databases.

Can Amazon ElastiCache be used for session management?

• A) Yes
• B) No

Answer: A) Yes

Explanation: Amazon ElastiCache is often used for caching session management data, as it can improve application performance and user experience.

In AWS, Cache eviction happens automatically when the cache memory is filled. (True/False)

• True
• False

Answer: True.

Explanation: When the memory limit is reached, AWS ElastiCache uses an eviction policy to determine which items to remove from the cache.

Amazon ElastiCache is used to cache database query results. (True/False)

• True
• False

Answer: True

Explanation: Amazon ElastiCache improves the performance of web applications by allowing you to retrieve information from fast, managed, in-memory caches, instead of relying entirely on slower disk-based databases.

Interview Questions

What is caching in the context of AWS?

Caching in the context of AWS is a method to store copies of files in a temporary storage area (cache) so that they are more readily available to users. This can significantly improve application performance by providing quick read access to data stored in slower backend systems.

Which AWS service provides a in-memory data store with sub-millisecond latency?

Amazon ElastiCache provides a high-performance, in-memory data store that offers sub-millisecond latency.

What types of caching does Amazon CloudFront supports?

Amazon CloudFront supports both edge caching and regional caching.

What is a TTL in the context of AWS caching?

TTL or Time To Live in the context of AWS caching refers to the duration for which a file is kept in the cache before being refreshed or removed. It is defined by the user to control how frequently CloudFront needs to go to your origin to check for an updated version of that file.

How does Amazon ElastiCache enhance the performance of web applications?

Amazon ElastiCache enhances the performance of web applications by allowing you to retrieve information from fast, managed, in-memory data stores, instead of relying entirely on slower disk-based databases.

Which caching engine does Amazon ElastiCache support?

Amazon ElastiCache supports two popular open-source in-memory caching engines: Memcached and Redis.

What is Cache Hit Ratio in the context of AWS ElastiCache?

Cache Hit Ratio refers to the ratio of cache hits to total requests. This ratio can be used as an indicator of the efficiency of your cache, with a high ratio indicating high cache usage and potential performance improvements.

What’s the difference between ElastiCache for Redis and ElastiCache for Memcached?

ElastiCache for Redis offers rich data structures, persistence, and built-in replication, with added abilities like pub/sub capabilities and sorting capabilities. It is ideal for supporting complex manipulations. ElastiCache for Memcached is ideal for simple key-value stores as it is easy to use and simplifies the process of horizontally scaling out caches.

What is Amazon CloudFront in the context of caching?

Amazon CloudFront is a content delivery network (CDN) service that securely delivers data, videos, applications, and APIs to customers globally with low latency and high transfer speeds. It caches content at edge locations close to the end-user to improve the speed and reduce the load on the origin.

How is cache invalidation handled in Amazon CloudFront?

In Amazon CloudFront, you can either invalidate individual files, or you can invalidate multiple files simultaneously by using wildcard (*) characters in the file path names. This allows the outdated or stale versions of the files to be removed from CloudFront edge caches.

What is the role of AWS Elastic Beanstalk in caching?

AWS Elastic Beanstalk automatically provisions an Amazon ElastiCache instance and connects it to your environment, making it easier to use caching in your applications.

What are cache nodes in the context of ElastiCache?

In ElastiCache, cache nodes are base units of computational resources. Each cache node has its own DNS name and port, and processes running on these cache nodes can partition data across multiple nodes.

Which AWS services can be used to distribute content with caching?

Amazon CloudFront and Amazon API Gateway both provide content caching features to distribute content closer to users’ locations.

Can you use Memcached and Redis together in the same ElastiCache cluster?

No, you have to choose one caching engine for each ElastiCache cluster.

What considerations should you make when choosing between Amazon ElastiCache for Redis and Amazon ElastiCache for Memcached?

The choice between the two depends on your application’s requirements. If you need a simple, in-memory cache with the ability to scale horizontally, you could use Memcached. If you need a more feature-rich solution that includes persistence and complex data types, you could use Redis.