* The traffic which originated from the internet and for these private instance that's comes via ELB
* ELB work as a Reserve Proxy
* NAT Gateway work as a Forward proxy
* NAT Gateway should place in pulic subnet
* ELB should place in public or private subnet
* NAT and ELB both are the managed services but NAT Gateway live in one subnet as a ELB if we choose correctly can spam in multiple subnet
* In NAT we have two options NAT instace and NAT Gateway
* NAT Gateway can live only one availability zone or we can choose only one subnet for one instance
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Elastic Load Balancer
* ELB is mananged service by amazon
* ELB distribute the taffic to n number of instances which are registed to ELB
* ELB does check continious health check which are registred to ELB, in case any intance become unhealthy ELB will stop send traffic to that particular instance.
* Intenaly ELB launch the instance so it consomme the IP from your subnet hence keep some buffer in terms of private IP address
* You can move Web-server to private subnet and keep only ELB in public Subnet. Within a VPC all instances can talk to each other(irrespective of subnet)
* Traffic gets distributed between 2 AZs in roub-robin fashion, with in AZ there are n number of instances and request will go which have lease of connections
* ELB should be access by DNS not by IP address
* If we use check botton "Create an internal load balancer" then it will be private load balancer
* If we know the URL then we do choose httpd and URL path ohterwise we should choose TCP
* And you have to enable Cross-Zone Load Balancing and enable Connection Draining, it will distribute traffic in all instance of all AZ equaly
* And connection draining is a time which ELB we give to that unhealthy instance has some open connections with in particular time instance can relese his connection
Appilcation Load Balancer
* If configured a clasic load balancer and register N number of ec2 instance then every instance would have same type of content or would have all the file similar
* Where as in case of application load balancer we can go head and create rules based on which any incoming request can go to specific target group
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