1.Elastic Load balancer is region specific
2.An ELB listener is the process that checks for connection requests. There are front end listeners facing users and backend listener communicating with EC2 instances
3.Listners process HTTP, HTTPS, TCP, SSL protocols.
4.Front end Listeners check for traffic from client and Backend listeners check for predefined port to check for traffic from ELB to EC2 instances
5.It would take some time for the registration of EC2 instances with ELB.
6.Registered EC2 INSTANCES are those that are defined under ELB
7.ELB has nothing to do with outbound traffic that is initiated from registered EC2 instances destined to Internet or to any other instance within VPC.
8.ELB has to do with inbound traffic destined to EC2 registered instances and the respective return traffic
9.ELB is charged hourly .
10.If you do not want the ELB to be charged, you can delete it.
11.Before you delete ELB, it is recommended that you point Route 53 to somewhere else other than ELB.
12.Deleting ELB does not affect or deleted the registered EC2 instances with it.
13.ELB forwards traffic to Eth0 of registered instance
14.Incase EC2 registered instance has multiple IP address in eth0, ELB will forward traffic to its primary IP address.
15.ELB supports IPV4 only
16.To ensure that ELB service can scale ,ELB node in each AZ ensure that the subnet defined for load balancer is at least /27 in size and has at least 8 available IP address ,the ELB nodes can use to scale.
At least 8 free IP address should be reserved for ELB.
17.For fault tolerance it is recommended that you register your EC2 instances across availability zones within the VPC region
18.If possible, try to allocate the equal number of EC2 instances equally within different Availability zones connected to Load balancer.
19.Load Balancer monitors the health of all registered EC2 instances and it send traffic only to healthy instances.
20.As soon as unhealthy instance becomes healthy Load balancer again sends traffic to that EC2 instance.
21.Registered instances must responmd with http 200 ok” message to notify ELB that it is healthy.
22.AWS API uses ping TCP(port 80) for health checks and through console uses http for health check.
23.By default response time is 5 sec.Can be set from 5 sec to 300 sec to declare unhealthy instance.
24.Unhealthy thresholds–by defuault 2 but can be changed to max to 10 .
25.Bydefault ,ELB distributes traffic evenly between AZ it is defined i without consideration to number of Registered EC2 instances in each AZ.–Solution is Cross Zone Load Balancing.
26.Cross Zone load balancing is disabled by default.Once enabled, ELB will distribute traffic equally based on number of registered EC2 instances in AZ.
27-ELB name you choose must be unique within the account
28-ELB is region specific, so all registered EC2 instances must be in same region, but can be in different AZ.
29-To define your ELB, you can select one subnet in that AZ. Subnet can be public or pvt.
30-Only one subnet can be defined for the ELB in AZ
31-If you try and select another one in the same AZ, it will replace the former one
32.If you register instance in an AZ with ELB, but do not define a subnet in that AZ for the ELB, these instances will not receive traffic from ELB.
33.ELB should always be accessed using DNS an dnot from IP.
34.ELB can be internet facing or Internal ELB ec2 facing.
35.Internet facing ELB–ELB nodes will have pubic IP address .DNS will resolve the ELB DNS name to these IP address. If routes traffic to pvt IP address of your registered EC2 instance.
36.You need one Public Subnet in each AZ where the internet facing ELB will be defined, such that the ELB will be able to route internet traffic
37.Format of the public ELB DNS name of internet facing ELB–
38.Format of Internal ELB DNS name
internal-name 123456789 region.elb.amazon.aws.com
39-An ELB Listener is the process that checks for connection request.
40-Each Network Load balancer needs at least one listener tp accept traffic.
41-You must assign a security group to your ELB. This will control traffic that can reach your ELB front end listeners.
42–Target Group–Logical grouping of targets behind the load balancers. Target group can be exist independently from load balancer. Target group can be associated with an auto scaling group. Target group can contain up to 200 targets.
43.Path-Based Routing = Application Load Balancer.You can create a listener with rules to forward requests based on the URL path. This is known as path-based routing. If you are running microservices, you can route traffic to multiple back-end services using path-based routing. For example, you can route general requests to one target group and requests to render images to another target group.
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