November 16, 2022

Top 20 AWS ElastiCache Interview Questions and Answers

 

         Web services like Amazon ElastiCache make it simple to set up and manage Memcached or Redis protocol-compliant server nodes in the cloud. With Amazon ElastiCache, you may get data from a quick, controlled, in-memory system rather than only relying on slower disk-based databases, which increases the speed of web applications. Your engineering resources may concentrate on creating applications as a result of the service's simplification and offloading of in-memory environment administration, monitoring, and operation. You may use Amazon ElastiCache to decrease the cost of scaling online applications while also enhancing load and response times to user actions and queries.

 

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Ques: 1). What is Amazon ElastiCache?

Answer:

Common administrative activities needed to run a distributed in-memory key-value environment are automated by Amazon ElastiCache. With a few clicks on the AWS Management Console, you can quickly add a caching or in-memory layer using Amazon ElastiCache to your application design. A robust solution that reduces the danger of overcrowded databases, which degrade website and application load times, is provided by Amazon ElastiCache after a cluster is established. This technology automatically identifies and replaces failing nodes. The integration of Amazon ElastiCache with Amazon CloudWatch monitoring improves insight into the crucial performance indicators related to your nodes. Because Memcached and Redis are protocol-compliant, you may use the same code, programmes, and well-known tools you already use with your current Memcached or Redis installations with Amazon ElastiCache. With Amazon ElastiCache's support for clustered configuration, you can take advantage of a managed service that is quick, scalable, and simple to use while still being able to handle the demands of your most demanding applications. There are no upfront costs involved, and you just pay for the resources you use, like with other Amazon Web Services.

 

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Ques: 2). What are the nodes, shards, and clusters of Amazon ElastiCache?

Answer:

The smallest component of an Amazon ElastiCache setup is a node. It is a fixed-size portion of safely connected network RAM. Each node has its own DNS name, port, and instance of the Memcached or Redis protocol-compliant service. There are several different types of supported nodes, each with a different amount of memory. A Redis shard is a portion of the cluster's keyspace, which may consist of a primary node and 0–n read replicas.


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Ques: 3). What is handled on my behalf by Amazon ElastiCache?

Answer:

The setup of a distributed in-memory environment is handled by Amazon ElastiCache, which also handles the provisioning of the server resources and software installation. The solution automates routine administrative chores like failure detection and recovery and software patching once your environment is operational. You may rapidly identify problems by using the precise monitoring metrics that Amazon ElastiCache offers for your nodes. For instance, if one of your nodes becomes overwhelmed with requests, you may set up thresholds and get alarms.


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Ques: 4). Amazon ElastiCache Reserved Nodes: What are they?

Answer:

When you commit to a one-year or three-year term, reserved nodes or reserved instances (RI) provide you a considerable discount over on-demand use. With Reserved Nodes, you may make a one-time, upfront payment to create a one- or three-year reservation to run your node in a certain Region and save a lot of money compared to the regular hourly usage fee. You may balance the upfront payment with your hourly rate by choosing one of three Reserved Node types: All Upfront, No Upfront, or Partial Upfront.


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Ques: 5). A maintenance window is what? My nodes will be accessible during software maintenance, right?

Answer:

You might consider the Amazon ElastiCache maintenance window as a chance to decide when software patches are applied, should that be requested or necessary. If a "maintenance" event is planned for a specific week, it will start and end at the designated 60-minute maintenance window.

If software patching is planned during your maintenance window, your nodes can experience some outage. For further information, please see Engine Version Management. Patching may be requested by the user, such as when upgrading the cache software, or it may be deemed necessary (if we identify any security vulnerabilities in the system or caching software). Software patches should seldom take up more than a small portion of your maintenance window as they are applied infrequently (usually once every few months). A default value of 60 minutes is applied if you do not provide a desired weekly maintenance window when configuring your Cluster. By updating your DB Instance in the AWS Management Console or by using the ModifyCacheCluster API, you may change when maintenance is carried out on your behalf. If you like, each of your Clusters may have a distinct preferred maintenance window.


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Ques: 6). Why do I need a subnet group and what does it accomplish?

Answer:

For your Amazon ElastiCache Cluster in a VPC, you must specify a Subnet Group, which is a group of subnets. With the help of the Amazon ElastiCache Console, a Subnet Group is formed. There should be at least one subnet in each subnet group. The Subnet Group is used by Amazon ElastiCache to choose a subnet. The Node Endpoints are next connected to the IP Addresses from the chosen subnet. In addition, nodes with the aforementioned IP addresses are connected to via Elastic Network Interfaces that Amazon ElastiCache builds.

Because the underlying IP addresses for your nodes might vary, Amazon highly advises using the DNS Names to connect to them (e.g., after cache node replacement).


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Ques: 7). When does the contract for a Reserved Node start if I sign up for one? What occurs to my node at the conclusion of the term?

Answer:

When your request is accepted, the pricing adjustments related to a Reserved Node are triggered while the payment authorization is being handled. On the AWS Account Activity page or by using the DescribeReservedCacheNodes API, you may monitor the progress of your reservation. The discounted pricing will not apply if the one-time payment cannot be authorised by the end of the subsequent billing cycle.

Your Reserved Node will go back to the appropriate On-Demand hourly use charge for your node class and location after your reservation period expires.


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Ques: 8). How do I pick my Cluster's configuration settings correctly?

Answer:

By default, Amazon ElastiCache selects the cluster's ideal configuration settings based on the Node Type's memory and compute resource availability. However, you can modify them if necessary by utilising our configuration management APIs. Please be aware that altering configuration settings from suggested values might result in unanticipated consequences such as performance degradation or system failures and should only be done by experienced users who are willing to take these risks.


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Ques: 9). Today, I employ Memcached. Why should I switch to Amazon ElastiCache?

Answer:

Memcached and Amazon ElastiCache both adhere to the same protocol. As a result, you may utilise common Memcached operations like get, set, incr, and decr precisely as you would in your current Memcached installations. The text and binary protocols may both be used with Amazon ElastiCache. Additionally, it supports the most of the common statistic results, which are also available via CloudWatch as graphs. Because the libraries you use will still function, you may switch to utilising Amazon ElastiCache without recompiling or re-linking your apps. You only need to edit your application's Memcached configuration file to include the endpoints of the servers (nodes) we supply for you in order to setup the cache servers your application visits. To retrieve a list of the endpoints, you can just use the "DescribeCacheClusters" API or the "Copy Node Endpoints" option on the AWS Management Console. Before completing the switchover from your current solution, Amazon advises extensive testing of your new Amazon ElastiCache setup, as with any migration procedure.


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Ques: 10). A cluster may potentially cover more than one Availability Zone, is it true?

Answer:

Yes. You can select the availability zones for the new nodes while building a cluster or adding nodes to an existing cluster. Either choose "spread nodes across zones" or enter the desired number of nodes in each availability zone. Nodes can only be deployed in availability zones that are a part of the chosen cache subnet group if the cluster is in a VPC.


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Ques: 11). How do other Amazon Web Services and Amazon ElastiCache interact?

Answer:

As a front-end for Amazon Web Services like Amazon RDS and Amazon DynamoDB, Amazon ElastiCache is perfectly suited since it offers exceptionally low latency for high speed applications and offloads some of the request traffic while these services guarantee long-lasting data durability. Along with Amazon EC2 and EMR, the service may also be leveraged to enhance application performance.

 

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Ques: 12). What are the steps for utilising Auto Discovery?

Answer:

Click the "Download ElastiCache Cluster Client" link on the Amazon ElastiCache interface to begin downloading the Amazon ElastiCache Cluster Client. You need an Amazon ElastiCache account before you can download; if you don't currently have one, you may create one from the Amazon ElastiCache information page. By going to the Amazon ElastiCache console after downloading the client, you can start configuring and activating your Amazon ElastiCache cluster.

 

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Ques: 13). How can I tell my cluster to run the supported version of Memcached?

Answer:

When constructing a new cluster, you can choose any minor or major version that is currently supported. Using the "Modify" option for your cluster, you can start an upgrade to a supported engine version release. Simply enter the desired version into the "Cache Engine Version" column. If the "Applied Immediately" option is selected, the update will then be carried out on your behalf either right away or during the subsequent cluster maintenance session.


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Ques: 14). How can in-memory caching benefit my applications?

Answer:

With the help of Amazon ElastiCache's in-memory caching, many read-heavy application workloads (including social networking, gaming, media sharing, and Q&A portals) or compute-intensive workloads can experience a considerable reduction in latency and throughput (such as a recommendation engine). By keeping important data in memory for quick access, in-memory caching enhances application performance. The outcomes of computation- or I/O-intensive calculations as well as the results of database queries may both be included in cached data.

 

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Ques: 15). How can I build a cluster?

Answer:

Using the AWS Management Console, Amazon ElastiCache APIs, or Command Line Tools, cluster creation is straightforward. Click the "Create" button in the "Memcached" or "Redis" tab of the AWS Management Console to start a cluster. To build a cluster with the required amount of RAM, you only need to give your Cluster Identifier, Node Type, and Number of Nodes. As an alternative, you may build your cluster using the elasticache-create-cache-cluster command or the CreateCacheCluster API. When you create a cluster, AWS will automatically deploy it in an Availability Zone depending on your memory needs and available capacity if you do not select one.

 

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Ques: 16). When utilising VPC is not an option, How does the Cache Security Groups in Amazon ElastiCache let you manage access to your clusters?

Answer:

A Security Group controls network access to your cluster similarly to a firewall. Your clusters' network access is disabled by default. You must explicitly permit access from hosts in particular EC2 security groups if you want your apps to be able to access your cluster. Ingress is the name of this procedure.

Create a Security Group and link it to the required EC2 security groups (which in turn define the EC2 instances authorised) to grant network access to your cluster. When creating your cluster, the Security Group can be linked to it, or you can do it later by selecting "Modify" from the AWS Management Console.

 

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Ques: 17). With Amazon ElastiCache for Memcached, what can I cache?

Answer:

Using the service, you can cache a wide range of objects, including transient session data that might not need a persistent backing store, dynamically generated web pages (using, for instance, Nginx), and content in persistent data stores (like Amazon RDS, DynamoDB, or self-managed databases hosted on EC2). Additionally, you may use it to install admission control in high traffic online applications by implementing high-frequency counters.

 

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Ques: 18). How do I control network access to my cluster?

Answer:

In non-VPC installations, Amazon ElastiCache enables you to manage access to your cluster and, therefore, the nodes, using Security Groups. A Security Group controls network access to your node similarly to a firewall. Your nodes' network access is disabled by default. You may configure your Security Group to permit access from EC2 Instances with a certain EC2 Security Group membership or IP ranges if you want your apps to have access to your node. Ingress is the name of this procedure. All nodes included in a Security Group must abide by the same rules once ingress has been set for that Security Group. The "Security Groups" section of the Amazon ElastiCache Console or the Amazon ElastiCache APIs may be used to configure security groups.

 

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Ques: 19). How will I be charged and billed for my use of Amazon ElastiCache?

Answer:

There is no minimum charge; you simply pay for what you really use. For each Node Type, pricing is based on utilised Node-hours. Node-hours that are utilised in part are invoiced as full hours. Within the same Availability Zone, there are no fees associated with data transmission between Amazon EC2 and Amazon ElastiCache. You are only billed for data transfers into or out of the Amazon EC2 instance, even if regular Amazon EC2 Regional Data Transfer fees apply when moving data between an Amazon EC2 instance and an Amazon ElastiCache Node in different Availability Zones of the same Region. For traffic entering or leaving the Amazon ElastiCache Node itself, there is no Amazon ElastiCache Data Transfer fee. For data transported outside of an area, standard data transfer rates apply.

 

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Ques: 20). Which well-known Memcached libraries work with Amazon ElastiCache?

Answer:

LibMemcached (C) and libraries based on it (e.g. PHP, Perl, Python), spyMemcached (Java), and fauna are some examples of existing Memcached client libraries that function with Amazon ElastiCache without the need to recompile or re-link applications (Memcached 1.4.5 and later) (Ruby).

 

 

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