Top AWS ElastiCache Interview Questions and Answers

Introduction

In the Amazon Web Services (AWS) ecosystem, Amazon ElastiCache offers beginners a powerful tool to enhance their applications' performance and scalability by acting as a managed in-memory caching system, enabling swift access to frequently used data. This speeds up application response times and reduces database load, improving overall efficiency. For AWS beginners preparing for interviews, our AWS ElastiCache interview questions and answers will help you learn how to optimize application performance and leverage AWS services effectively.

Q1: What Is AWS ElastiCache?

A: Amazon ElastiCache is a web service that simplifies the setup and management of distributed in-memory caching environments. This service makes it easy and cost-effective to provide a high-performance and scalable caching solution for your cloud applications. You can use Amazon ElastiCache in your applications to speed the deployment of cache clusters and reduce the administration required for a distributed cache environment.

With Amazon ElastiCache, you can choose from a Memcached or Redis protocol-compliant cache engine and quickly launch a cluster within minutes. Because Amazon ElastiCache is a managed service, you can start using the service today with very few or no modifications to your existing applications that use Memcached or Redis. Because Amazon ElastiCache is protocol-compliant with both engines, you only need to change the endpoint in your configuration files.

Q2: What Are The Drawbacks Of ElastiCache?

A: One drawback of ElastiCache is that it doesn't support automatic failover from one AWS Region to another. If needed, you'll have to manually promote a secondary cluster. For example, you can promote the secondary cluster to primary. To start with existing data, you can use an existing cluster as primary to create a global data store.

Q3: What Is Memcached Auto Discovery?

A: Amazon ElastiCache supports Auto Discovery with the provided client library for Memcached clusters partitioned across multiple nodes. Auto Discovery simplifies your application code by eliminating the need to be aware of the cache cluster's infrastructure topology in your application layer.

Q4: What Are Multi-AZ Replication Groups?

A: You can also create a Multi-AZ replication group, which allows you to increase availability and minimize data loss. Multi-AZ simplifies dealing with a failure by automating the replacement and failover from the primary node.

If the primary node fails or can't be reached, Multi-AZ will select and promote a read replica to become the new primary, and a new node will be provided to replace the failed one. Amazon ElastiCache will then update the Domain Name System (DNS) entry of the new primary node to allow your application to continue processing without any configuration change and with only a short disruption.

Q5: When Does The Contract For A Reserved Node Start If I Sign Up For One? What Happens To My Node At The End Of The Term?

A: When you request a Reserved Node, the pricing changes happen when the payment is being processed. You can track this on the AWS Account Activity page or with the DescribeReservedCacheNodes API. If the one-time payment isn't authorized by the end of the next billing cycle, you won't get the discounted price. At the end of the reserved period, your node goes back to regular hourly charges.

Q6: How Do I Choose My Cluster's Configuration Settings Correctly?

A: Normally, Amazon ElastiCache picks the best configuration settings for your cluster based on the memory and computing resources of your Node Type. But if needed, you can change them using our configuration management tools. Just know that changing these settings from the defaults could cause problems like slower performance or system crashes. It's best done by experienced users who understand the risks.

Q7: What Are The Nodes, Shards, And Clusters Of Amazon ElastiCache?

A: Nodes: Nodes are the basic parts of Amazon ElastiCache. They're like small pieces of memory that are securely connected to a network. Each node has its own name, port, and runs either Memcached or Redis service.

Shards: A Redis shard is a part of the cluster's storage area, which can include a main node and some read replicas.

Clusters: A cluster is a group of nodes and shards working together.

Q8: If I Can't Use VPC, How Do Cache Security Groups In AWS ElastiCache Help Control Access To My Clusters?

A: A cache Security Group is like a gatekeeper for your cluster, deciding who can come in and who can't, kind of like a firewall. By default, nobody can get into your cluster's network. If you want your apps to talk to your cluster, you must permit them. This process is called "Ingress."

To let your apps in, you create a Security Group and link it to specific groups of computers (called EC2 security groups) that your apps run on. This way, only those computers can access your cluster. When you make your cluster, you connect it to the Security Group, or you can do it later through the AWS Management Console.

So, even if you can't use VPC, Cache Security Groups ensure only suitable computers can access your cluster, keeping your data safe.

Q9: What Are Subnet Groups In Amazon ElastiCache?

A: In ElastiCache, a subnet group is like a group of friends you hang out with in a specific place.

You pick a subnet group when you set up a cache cluster or a replication group. This tells ElastiCache which area of the Internet (VPC) and which parts of that area (subnets) to use. It's like saying, "We're going to this part of town to hang out."

Using a subnet group helps keep your cache cluster or replication group working even if one part of the Internet goes down. ElastiCache is still not using the other parts if one area isn't working. So, a subnet group is essential because it tells ElastiCache where to set up shop and helps keep things running smoothly even if there's a problem in one area.

Q10: Today, If I Employ Memcached. Why Should I Switch To Amazon ElastiCache?

A: If you're already using Memcached, switching to Amazon ElastiCache has several benefits. Both Memcached and ElastiCache follow the same protocol, so you can continue using common Memcached operations like get, set, incr, and decr just like before. ElastiCache supports both text and binary protocols, and it provides most of the same statistic results, which you can also view through CloudWatch as graphs.

The good news is that your existing libraries will still work, so you won't need to recompile or re-link your applications. All you have to do is update your application’s Memcached configuration file to include the endpoints of the servers (nodes) provided by Amazon for setting up the cache servers your application accesses.

You can easily get a list of these endpoints using the “DescribeCacheClusters” API or the “Copy Node Endpoints” option on the AWS Management Console. However, before fully transitioning to Amazon ElastiCache, it's important to thoroughly test your new setup to ensure everything works smoothly, just like with any migration process.

Q11: What Are Data Access Patterns?

A: Retrieving a flat key from an in-memory cache will always be faster than the most optimized database query. You should evaluate the data's access pattern before storing it in the cache. An excellent example of something to cache is the list of products in a catalog. For a busy website, the list of items could be retrieved thousands of times per second. While it makes sense to cache the most heavily requested items, you can also benefit from caching items that are only sometimes requested.

Some data items should also not be cached. For example, you should not cache the page results if you generate a unique page for every request. However, even though the page changes every time, it does make sense to cache the non-changing components of the page.

Q12: How Does AWS ElastiCache Work With Other Amazon Web Services (AWS)?

A: Amazon ElastiCache is a service provided by Amazon Web Services (AWS) that helps speed up web applications by storing data in memory. Here, it works with other AWS services:

• Amazon RDS: ElastiCache can speed up web apps by storing commonly used data from Amazon RDS, an AWS database service.

• Amazon EC2: ElastiCache can team up with Amazon EC2, which provides computers in the cloud, to build powerful web apps. EC2 computers can talk to ElastiCache to get data quickly.

• Amazon CloudWatch: ElastiCache works with Amazon CloudWatch, a service that keeps an eye on your AWS stuff, to help you keep track of how your cache is doing.

• Amazon SNS: ElastiCache also works with Amazon SNS, a messaging service, to send you messages when something important happens with your cache.

So, ElastiCache can partner with many other AWS services to make your web apps faster and easier to manage.

Q13: What Are The Two Different Types Of Scaling In Amazon ElastiCache?

A: Amazon ElastiCache allows you to adjust your environment's size to meet the workloads' needs as they evolve. Adding additional cache nodes lets you quickly expand horizontally and meet higher read or write performance levels. You can also select different classes of cache nodes to scale vertically.

Horizontal Scaling- Amazon ElastiCache also adds additional functionality that allows you to scale the size of your cache environment horizontally. This functionality differs depending on the cache engine you have selected. With Memcached, you can partition your data and scale horizontally to 20 nodes or more. With Auto Discovery, your application can discover Memcached nodes added or removed from a cluster.

Vertical Scaling—Amazon ElastiCache's support for vertical scaling is more limited. If you would like to change the cache node type and scale the compute resources vertically, the service does not directly allow you to resize your cluster in this manner. You can, however, quickly spin up a new cluster with the desired cache node types and start redirecting traffic to the new cluster. It's important to understand that a new Memcached cluster always starts empty, while a Redis cluster can be initialized from a backup.

Q14: How Does Backup And Recovery Work In Amazon ElastiCache?

A: Amazon ElastiCache clusters running Redis allow you to persist your data from in-memory to disk and create a snapshot. Each snapshot is a complete clone of the data that can be used to recover to a specific time or create a copy for other purposes. Snapshots cannot be created for clusters using the Memcached engine because it is a purely in-memory key/value store and always starts empty. Amazon ElastiCache uses the native backup capabilities of Redis and will generate a standard Redis database backup file that gets stored in Amazon Simple Storage Service (Amazon S3).

Snapshots require compute and memory resources and can impact the performance of heavily used clusters. Amazon ElastiCache will try different backup techniques depending on the available memory. A best practice is to set up a replication group and perform a snapshot against one of the read replicas instead of the primary node.

In addition to manually initiated snapshots, snapshots can be created automatically based on a schedule. You can also configure a window for the snapshot operation to be completed and specify how many days of backups you want to store. Manual snapshots are stored indefinitely until you delete them.

Q15: How Is The Access To The Amazon ElastiCache Cluster Controlled?

A: Access to your Amazon ElastiCache cluster is controlled primarily by restricting inbound network access to your cluster. Inbound network traffic is restricted through the use of security groups. Each security group defines one or more inbound rules that restrict the source traffic. 

When deployed inside a Virtual Private Cloud (VPC), each node will be issued a private IP address within one or more subnets you select. Individual nodes can never be accessed from the Internet or Amazon EC2 instances outside the VPC. You can further restrict network ingress at the subnet level by modifying the network Access Control Lists (ACLs).

Access to manage the cluster's configuration and infrastructure is controlled separately from access to the actual Memcached or Redis service endpoint. Using the AWS Identity and Access Management (IAM) service, you can define policies that control which AWS users can manage the Amazon ElastiCache infrastructure.

An administrator can perform key actions such as creating, Modifying or Deleting Cache Clusters. Redis clusters also support the CreateReplicationGroup and CreateSnapshot actions.

Q16: What Does Amazon ElastiCache Do?

A: Amazon ElastiCache helps make web applications faster by storing frequently used data in memory. This is handy for apps that often fetch data from a database because it's quicker to get data from memory than from a disk-based database like Amazon RDS.

Here are some common uses for ElastiCache:

• Caching database results: If your app keeps asking the same questions to the database, ElastiCache can save the answers in memory. This means fewer trips to the database.

• Storing session info: If your app remembers who's logged in, ElastiCache can store that info in memory, making it faster to check.

• Doing quick analytics: With ElastiCache using Redis, you can quickly analyze big data sets in real-time. Redis has the tools to crunch numbers fast.

• Sending messages: ElastiCache with Redis can help apps send messages back and forth efficiently. It's like passing notes in class, but faster.

In short, ElastiCache can make your web app faster and handle more users by storing data in memory.

Q17: How Do I Choose The Proper Setup For My ElastiCache Cluster?

A: When setting up your Amazon ElastiCache cluster, there are a few essential things to think about:

• Cache engine: Decide if you want to use Memcached or Redis. Each has different features.

• Cache node type: Choose the type of computer you need based on how much power and storage you require.

• Number and size of cache nodes: Figure out how many computers you need and how much memory each should have. This depends on your workload and how fast you need things to be.

• Cluster mode (for Redis): If you're using Redis, decide whether you want a standard or cluster setup. Each has its pros and cons.

• Backup and restore: Think about if you want to back up your data regularly to keep it safe.

Consider these factors carefully to pick the best setup for your needs.

Q18: How Can Using In-Memory Caching Help My Apps?

A: Amazon ElastiCache is a service that makes it easy to set up and manage a particular memory cache in the cloud. This cache stores data that your apps use, making it quicker to access.

Here's why is why using ElastiCache can help your apps:

• Speeds up performance: Storing data in this memory cache can make your apps much faster because they don't always have to keep fetching the same data from a database. This also lightens the load on your database, making your whole system more responsive.

• Cuts down wait times: Since the data is stored in memory, your apps can grab it super fast, reducing the time your users have to wait for things to load.

• Scales easily: ElastiCache can handle sudden increases in users without you having to do anything. It automatically adds more memory space when needed.

• Keeps things running: ElastiCache is built to work even if parts break. It spreads the data across different places to ensure it's always available.

So, ElastiCache can speed up your apps, handle more users, and keep everything running smoothly.

Q19: What Is The Difference Between Memcached And Redis?

A: Amazon ElastiCache allows you to quickly deploy clusters of two popular cache engines: Memcached and Redis. At a high level, Memcached and Redis may seem similar, but they support different use cases and provide different functionality.

Memcached- Memcached provides a straightforward interface that allows you to write and read objects into in-memory key/value data stores. With Amazon ElastiCache, you can grow and shrink a cluster of Memcached nodes to meet your demands. 

You can partition your cluster into shards and support parallelized operations for high-performance throughput. Memcached deals with objects as blobs that can be retrieved using a unique key. What you put into the object is up to you, and it is typically the serialized results from a database query. This could be simple string values or binary data.

Redis—In late 2013, Amazon ElastiCache added support for deploying Redis clusters. At the time of this writing, the service supports the deployment of Redis version 2.8.24 and a number of older versions. Beyond the object support provided in Memcached, Redis supports a rich set of data types like strings, lists, and sets.

Unlike Memcached, Redis supports persisting in-memory data onto disk. This allows you to create snapshots that back up your data and then recover or replicate from the backups. Redis clusters can also support up to five read replicas to offload read requests. In the event of the primary node's failure, a read replica can be promoted and become the new master using Multi-AZ replication groups.

Q20: Explain Nodes And Clusters In Detail.

A: Each deployment of Amazon ElastiCache consists of one or more nodes in a cluster. Depending on your use case and the necessary resources, you can choose from many different types of nodes. A single Memcached cluster can contain up to 20 nodes. Redis clusters are always made up of a single node; however, multiple clusters can be grouped into a Redis replication group.

The individual node types are derived from a subset of the Amazon EC2 instance type families, like t2, m3, and r3. The specific node types may change over time, but today, they range from a t2.micro node type with 555MB of memory up to an r3.8xlarge with 237GB of memory, with many choices in between. The t2 cache node family is ideal for development and low-volume applications with occasional bursts, but certain features may not be available. The m3 family is a good blend of compute and memory, while the r3 family is optimized for memory-intensive workloads.

Depending on your needs, your cluster or replication group may have a few large nodes or many smaller nodes. As demand for your application changes, you may also add or remove nodes occasionally. Each node type comes with a preconfigured amount of memory, with a small amount allocated to the caching engine and operating system.

In the event that Amazon ElastiCache detects a node's failure, it will provision a replacement and add it back to the cluster. During this time, your database will experience increased load because any requests that would have been cached will now need to be read from the database. For Redis clusters, Amazon ElastiCache will detect failure and replace the primary node. A read replica can be automatically promoted to primary if a Multi-AZ replication group is enabled.

Conclusion

Amazon ElastiCache is an essential aspect of Amazon Web Services (AWS), particularly for beginners preparing for AWS interviews, and JanBask Training's AWS courses can further bolster their understanding. With JanBask's comprehensive training, beginners gain hands-on experience implementing efficient solutions using ElastiCache, demonstrating proficiency in critical AWS services crucial for interviews.