Your company runs a customer facing event registration site This site is built with a 3-tier architecture with
web and application tier servers and a MySQL database The application requires 6 web tier servers and 6
application tier servers for normal operation, but can run on a minimum of 65% server capacity and a single
MySQL database. When deploying this application in a region with three availability zones (AZs) which
architecture provides high availability?
A.
A web tier deployed across 2 AZs with 3 EC2 (Elastic Compute Cloud) instances in each AZ inside an Auto
Scaling Group behind an ELB (elastic load balancer), and an application tier deployed across 2 AZs with 3 EC2
instances in each AZ inside an Auto Scaling Group behind an ELB. and one RDS (Relational Database Service)
instance deployed with read replicas in the other AZ.
B.
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each A2 inside an Auto
Scaling Group behind an ELB (elastic load balancer) and an application tier deployed across 3 AZs with 2 EC2
instances in each AZ inside an Auto Scaling Group behind an ELB and one RDS (Relational Database Service)
Instance deployed with read replicas in the two other AZs.
C.
d A web tier deployed across 2 AZs with 3 EC2 (Elastic Compute Cloud) instances in each AZ inside an Auto
Scaling Group behind an ELB (elastic load balancer) and an application tier deployed across 2 AZs with 3 EC2
instances m each AZ inside an Auto Scaling Group behind an ELS and a Multi-AZ RDS (Relational Database
Service) deployment.
D.
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each AZ Inside an Auto
Scaling Group behind an ELB (elastic load balancer). And an application tier deployed across 3 AZs with 2 EC2
instances In each AZ inside an Auto Scaling Group behind an ELB. And a Multi-AZ RDS (Relational Database
services) deployment.
Answer D. The key is highly available and event registration, which cannot be just ‘read’
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I agree with Mandu. The option is D because the database has to ensure high availability by choosing Multi-AZ feature. The main purpose of Multi-AZ is to provide HA.
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https://aws.amazon.com/premiumsupport/knowledge-center/rds-read-replica/
Issue
I need to configure my Amazon RDS DB instance read replica so that it can be written to. How can I do this?
Short Description
Amazon RDS DB instance read replicas are read-only by design. In certain scenarios you may need configure a DB instance read replica so that it is modifiable.
Resolution
You can configure an Amazon RDS DB instance read replica to be read/write by setting the read_only parameter to false for the DB parameter group that you create for your DB instance(s).
Seems we can configure read replica to be modified, In this case “B” is correct
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But MN, there is need architecture provides high availability.
IF in read replica need some configuration than Multi-AZ RDS (Relational Database
Service) deployment. then it is not high availability when compare .
so D is correct .
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answer d
http://highscalability.com/blog/2016/1/11/a-beginners-guide-to-scaling-to-11-million-users-on-amazons.html
https://www.airpair.com/aws/posts/building-a-scalable-web-app-on-amazon-web-services-p1
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D.
Read replicas are not suitable for HA. They are for read performance improvement only to reduce load on the master. So the RDS must be Multi AZ which only leaves C and D as viable.
C does not meet the 65% capacity requirement in event of AZ failure. Splitting it across two AZ only provides 50% HA.
D is correct as is splits across 3 AZ which would provide 66% in even of losing an AZ.
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Yes, I will go with D. RDS with Multi AZ is recommended for High availability
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What makes “D” better choice over “C”? Can someone please explain? Is it recovery against loss of 2 AZs?
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If you deploy to two AZs only, in case of an AZ blackout your server capacity can drop to 50% before scaling up.
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But question says it can run on a single DB. I agree on HA part, but can a read replica be promoted if a single DB instance (master) fails ? That’s why I believe on B even though a safer answer is D.
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The problem with B is that when you promote a Read Replica, the DB instance will be rebooted before it becomes available. This causes a downtime so does not satisfy the high availability requirement. See http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReadRepl.html#USER_ReadRepl.Promote
So D is the right answer.
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D is the answer
But, be noted that, Multi-AZ RDS does not provide “read ability” to standby DB.
Multi-AZ RDS is better than Read-replica in the way it better for scalability, and failover support.
Refer to: https://aws.amazon.com/rds/faqs/
[quote] …it precludes the standby from being accessed directly or used for read operations…
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D
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D
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D
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