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you need to change anything in the architecture to main…

Your application is using an ELB in front of an Auto Scaling group of web/application servers deployed across
two AZs and a Multi-AZ RDS Instance for data persistence. The database CPU is often above 80% usage and
90% of I/O operations on the database are reads. To improve performance you recently added a single-node
Memcached ElastiCache Cluster to cache frequent DB query results. In the next weeks the overall workload is
expected to grow by 30%. Do you need to change anything in the architecture to maintain the high availability or
the application with the anticipated additional load’* Why?

PrepAway - Latest Free Exam Questions & Answers

A.
Yes. you should deploy two Memcached ElastiCache Clusters in different AZs because the ROS Instance
will not Be able to handle the load It me cache node fails.

B.
No. if the cache node fails the automated ElastiCache node recovery feature will prevent any availability
impact.

C.
Yes you should deploy the Memcached ElastiCache Cluster with two nodes in the same AZ as the RDS DB
master instance to handle the load if one cache node fails.

D.
No if the cache node fails you can always get the same data from the DB without having any availability
impact.

Explanation:
Answer A is mentioning 2 clusters not 1 cluster (with 2 nodes). If a node fails due to a hardware fault in an
underlying physical server, ElastiCache will provision a new node on a different server.

10 Comments on “you need to change anything in the architecture to main…

  1. david says:

    No good answer.
    A is wrong because it says “two clusters, not 2 nodes”
    B is wrong because what if entire AZ fails?
    C is wrong just like B, in case the entire AZ fails, we are screwed.
    D is wrong, as with 30% inclrease the DB won’t handle the load alone.

    http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/FaultTolerance.html#FaultTolerance.Memcached
    “Mitigating Availability Zone Failures

    To mitigate the impact of an availability zone failure, locate your nodes in as many availability zones as possible. In the unlikely event of an AZ failure, you will lose only the data cached in that AZ, not the data cached in the other AZs.”

    https://aws.amazon.com/elasticache/faqs/
    Q: How does Amazon ElastiCache respond to node failure?

    The service will detect the node failure and react with the following automatic steps:

    Amazon ElastiCache will repair the node by acquiring new service resources, and will then redirect the node’s existing DNS name to point to the new service resources. For VPC installations, ElastiCache will ensure that both the DNS name and the IP address of the node remain the same when nodes are recovered in case of failure. For non-VPC installations, ElastiCache will ensure that the DNS name of a node is unchanged; however, the underlying IP address of the node can change.
    If you associated an SNS topic with your cluster, when the new node is configured and ready to be used, Amazon ElastiCache will send an SNS notification to let you know that node recovery occurred. This allows you to optionally arrange for your applications to force the Memcached client library to attempt to reconnect to the repaired nodes. This may be important, as some Memcached libraries will stop using a server (node) indefinitely if they encounter communication errors or timeouts with that server.

    As you see from the amazon docs,
    The right answer should be:
    Yes. you should deploy two Memcached ElastiCache nodes in different AZs because the RDS Instance will not Be able to handle the load It me cache node fails.




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