Elastic Load Balancing

Cloud Load Balancer

创建时间:2021-03-09 12:59

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1. Overview

What is ELB?
- ELB distributes your incoming traffic across multiple targets, such as EC2 instances, containers, and IP addresses, in one or more AZs
- It monitors the health of its registered targets, and routes traffic to the healthy targets
- Elastic Load Balancing help scale your load balancer as your incoming traffic change over time — automatically scale to the vast majority of workloads
Benefits
- Increase the availability and fault tolerance
- You could configure health checks, thus ELB monitor the health of the compute resources, LB only send requests to the healthy ones
How it works
- Listener
  - configure your LB to accept incoming traffic by specifying one or more listeners
  - a process that checks for connection requests
    - with a protocol
    - port number
- cross zone load balancing
  - we should enable it cause it could make sure traffic is well distributed
  - when client send request, it will first go through route 53, and route 53 will distribute traffic thus each lb node receives 50% of traffic (2 LB nodes in total )
- request routing
  - client — amazon dns service — return IP address to client side — client use the ip address to make call to LB
  - dns entry specify the TTL to 60 seconds, this ensure that the IP addresses can be remapped quickly in response to changing traffic

Similar to ELB overview, NLB has listener
- a listener checks for connection requests from clients, using the protocol and port number you configure, and then forwards requests to a target group
you can configure your health checks on a per target group basis
Health checks are performed on all targets registered to a target group that is specified in a listener rule for your load balancer.
functions at 4th layer of OSI, capable of handling millions of requests per second
- when receives a connection request, it selects a target from the target group for the default rule
- attempts to open a TCP connection to the selected target on the port specified in the listener configuration

Create a target group
- set target type, name, protocol, port number, health check method
Configure load balancer and listener
- Network mapping
  - select the VPC that you used for your EC2 instances
  - select AZ and then select public subnet for the AZ

Listener
- A listener is a process that checks for connection requests, using the protocol and port that you configure. The rules that you define for a listener determine how the load balancer routes requests to the targets in one or more target groups.
Target Groups
- Each target group is used to route requests to one or more registered targets. When you create a listener, you specify a target group for its default action. Traffic is forwarded to the target group specified in the listener rule. You can create different target groups for different types of requests

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