AWS ELASTIC LOAD BALANCING - ELB

· Distributes incoming application or network traffic across multiple targets, such as EC2 instances, containers ECS, and IP addresses, in multiple Availability Zones.

· When you create a load balancer, you must specify one public subnet from at least two Availability Zones. You can specify only one public subnet per AZ

GENERAL FEATURES

· Accepts incoming traffic from clients and routes requests to registered targets.

· Monitors the health of its registered targets and routes traffic only to healthy targets.

· Enable deletion protection to prevent your load balancer from being deleted accidently. Disabled by default.

· Deleting ELB wont delete the instances registered to it

· Cross Zone Load Balancing - when enabled, each load balancer node distributes traffic across registered targets in all enabled AZs

Three Types of Load Balancers

· Application Load Balancer

o Functions at the application layer, the seventh layer of the Open Systems Interconnection (OSI) model

o Allows HTTP and HTTPS

o At least 2 subnets must be specified when creating this type of load balancer.

o Components

§ A load balancer servers as the single point of contact for clients

§ A listener checks for connection requests from clients. You must define a default rule for each listener that specifies a target group, condition, and priority

§ Target group routes requests to one or more registered targets. You can register with multiple targets groups, and configure health checks on a per target group basis.

o Benefits

§ Support for path based and host based routing

§ Support for routing requests to multiple applications on a single EC2 instance

§ Support for registering targets by IP address, including targets outside of the VPC for the load balancer

§ Support for containerized applications

§ Support for monitoring the health of each service independently

o Cross-Zone load Balancing is always enabled (no cross zone)

o If you specify targets using instance ID traffic is routed using the private IP address specified in the primary network interface of the instance. If you specify targets using IP addresses you can route traffic to an instance using any private IP address from one or more network interfaces

o Supports load balancer generated cookies only for sticky sessions

o HTTP/2 support

o Web sockets Support

o Monitoring

§ CloudWatch metrics -retrieve statistics about data points for your load balancers and targets as an ordered set of time-series data, known as metrics

§ Access logs - capture detailed information about requests made to your load balancer and store them as log files in S3

§ Request tracing - track HTTP requests

§ CloudTrail logs - capture detailed information about calls made to the ELB API and store them in S3

· NETWORK LOAD BALANCER

o Static IP can be address can be provided; 1 per subnet

Nlb > tcp, can see the client IP , must attach an EIP (if public facing) otherwise a random IP will be created and assigned, cross zone load balancing -> SSL Termination

SSE can be used with SQS,

· ELB Monitoring Types

o Cloudwatch Metrics - health / Performance

§ BackEndConnectionErrors -> number of unsuccessful connections to backend instances

§ HealthyHostCount -> number of healthy instances registered

§ unHealthyHostCount -> number of unhealthy instances registered

§ HTTP Backend 2xx, 3xx, 4xx & 5xx

§ Latency -> number of seconds taken from registered instance to respond / connect

§ Request Count -> number of requests completed during the specified interval ( 1 or 5 mins )

§ SurgeQueueLength -> number of Pending requests, max queue size is 1024 , additional requests get rejected ( Classic Only)

§ SpillOverCount -> number of requests rejected because the surge queue is full (classic only)

o Access / ELB logs - who is accessing the site

§ can store data in S3 that has been deleted by the instance i.e 5xx etc, days after the event

o Request Tracing - ALB only - trace the connection internally to the AWs endpoint

o CloudTrail Logs - who provisioned the ELB etc

· ELB Other

o If expecting a sudden rise in traffic, contact AWS to pre-warm the ELB