You have developed a new web application in us-west-2 that requires six Amazon Elastic Compute Cloud
(EC2) instances running at all times. You have three availability zones available in that region (us-west-2a, uswest-2b, and us-west-2c). You need 100 percent fault tolerance if any single Availability Zone in us-west-2
becomes unavailable. How would you do this, each answer has 2 answers, select the answer with BOTH
correct answers.
A.
Answer 1 – Us-west-2a with two EC2 instances, us-west-2b with two EC2 instances, and us-west-2c with
two EC2 instances. Answer 2 – Us-west-2a with six EC2 instances, us-west-2b with six EC2 instances, and
us-west-2c with no EC2 instances
B.
Answer 1 – Us-west-2a with six EC2 instances, us-west-2b with six EC2 instances, and us-west-2c with no
EC2 instances. Answer 2 – Us-west-2a with three EC2 instances, us-west-2b with three EC2 instances, and
us-west-2c with three EC2 instances.
C.
Answer 1 – Us-west-2a with three EC2 instances, us-west-2b with three EC2 instances, and us-west-2c with
no EC2 instances. Answer 2 – Us-west-2a with three EC2 instances, us-west-2b with three EC2 instances,
and us-west-2c with three EC2 instances.
D.
Answer 1 – Us-west-2a with three EC2 instances, us-west-2b with three EC2 instances, and us-west-2c with
three EC2 instances. Answer 2 – Us-west-2a with four EC2 instances, us-west-2b with two EC2 instances,
and us-west-2c with two EC2 instances.
B
0
1
Can someone explain how the answer is B ?
0
1
The stress here, is to have 6 instances running any time, even if one site fails.
Lets take option A
Us-west-2a with two EC2 instances, us-west-2b with two EC2 instances, and us-west-2c withtwo EC2 instances
Here, if one AZ fails, there are only 2+2 instances running, which is short of 6
Now, option C
Us-west-2a with three EC2 instances, us-west-2b with three EC2 instances, and us-west-2c with no EC2 instances
Here, if 2a AZ fails, that leaves with 3 instances running, short of 6 again
Option D
Answer 2 – Us-west-2a with four EC2 instances, us-west-2b with two EC2 instances, and us-west-2c with two EC2 instances.
Here, if 2b or 2c fails, there is always 4+2 instances running.
But if 2a fails, that leaves us with 2+2 instances running, short of 6 again.
7
1