Thursday, 27 April 2017

Understanding ELB in depth - Query from Viewers - 003

Hi Guys,
I have got some good questions on ELB for the given tutorial --


1. you had mentioned that the ELB internally creates instances to manage traffic. Just to expand a little on this, So When this ELB creates the internal instance(i assume its not visible to us ) and it consumes the private IP's too right, Does the internal instance gets created per availability zone or per instance? Coz, I attach an ELB to the instance not to the A.Z ?right? I assume it's something like an agent which gets installed per instance and sort of polling the Domain LB? pls, correct my understanding? 
ANS: Yes, those instances won't be visible to users as ELB is a managed service. These instances do use ENIs (and hence Private IPs) from the respective subnets. ELB creates one instance in every subnet (you choose while ELB creation). There is no agent running on your instances (e.g. web server). Also, you register your instances to an ELB and hence tell ELB that it could send traffic to these instances.

2. Under Load balancers / instances, down the page under availability zone, ELB had created 2 AZ's. whereas I had all 3 of my instances in the same A.Z, though I can edit it and remove the other A.Z, why does it create an another AZ reference point when all my instances are in only one AZ? pls assist 
ANS: While creating ELB, you can clearly choose which subnets you want it to handle. It is recommended that you give 2 subnets in 2 different AZs (based on principle of HA). ELB will launch an internal instance in the subnets you choose while creating ELB.

3. Under health check, the ping target, I gave the path index.html. let's assume I have 2 instances and if I want the index.html to reside in a different location for all the 2 instance, let's assume for the 1st one, it's under var/www/HTML and for the second one if its under var/www ..does the ping target as the intelligence to check the file irrespective if its location?
ANS: Given the fact that all the instances behind an ELB are generally kept identical, the path of the file has to be same. Though, if you have some specific use-case for the above scenario, it could be achieved using Application Load Balancer. But, in Classic ELB, it has to be same path. 

KEEP practicing, keep LEARNING !!!
 

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