Your application’s Auto Scaling Group scales up too quickly, too much, and stays scaled when traffic decreases. What
should you do to fix this?
A.
Set a longer cooldown period on the Group, so the system stops overshooting the target capacity. The issue is that the scaling system
doesn’t allow enough time for new instances to begin servicing requests before measuring aggregate load again.
B.
Calculate the bottleneck or constraint on the compute layer, then select that as the new metric, and set the metric thresholds to the
bounding values that begin to affect response latency.
C.
Raise the CloudWatch Alarms threshold associated with your autoscaling group, so the scaling takes more of an increase in demand
before beginning.
D.
Use larger instances instead of lots of smaller ones, so the Group stops scaling out so much and wasting resources as the OS level,
since the OS uses a higher proportion of resources on smaller instances.
Explanation:
Systems will always over-scale unless you choose the metric that runs out first and becomes constrained first. You also
need to set the thresholds of the metric based on whether or not latency is affected by the change, to justify adding
capacity instead of wasting money.
http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/policy_creating.html
B
We are facing this problem while scale in and out (both). So there must be some problem with out metric of scaling so B is the right option. (Cooldown will not help here)
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A – you need to set the Cooldown (and warmpup) periods correctly for autosacling to scaleup correctly – not overshoot in either direction.
Auto Scaling Cooldowns: The Auto Scaling cooldown period is a configurable setting for your Auto Scaling group that helps to ensure that Auto Scaling doesn’t launch or terminate additional instances before the previous scaling activity takes effect.
http://docs.aws.amazon.com/autoscaling/latest/userguide/Cooldown.html
B is wrong, it simply is saying we have no idea – we have to start from the basics. C and D are just wrong
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I don’t think A is right.
1. Cooldown period will affect both scale-up and down. At the moment scale-up too quick and scale-down to slow, if we extend the Cooldown period, that will cause not scale-up or not scale-down.
2. B is saying we don’t know the correct metric, we need to find it out and reconfigure ASG.
The answer should be B
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Agreed. A does not solve the problem of `stays scaled when traffic decreases`.
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A
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Answer is : B.
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