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ELB Concepts

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  5. ELB Concepts
  • ELB is used to balance network traffic load
  • It load balances following
    • EC2 instances
    • containers
    • IP addresses
  • It load balances in multiple Availability Zones
  • Every load balancer is name as per DNS in format – {Balancer-name}.{region}-elb.amazonaws.com
  • Health monitoring of all nodes is done to prevent sending data to unhealthy nodes
  • Unhealthy nodes are detected, stopped sending data and wait till it turns healthy
  • Ports supported by ELB, are in range – 1-65535
  • Protocols supported by ELB, are
    • HTTP
    • HTTPS
    • TCP
    • SSL (Secure TCP)
  • Listener are configured on balancer to accept requests
    • Configuration involves specifying protocol and port number for listener and protocol and port number of nodes to send requests, to
  • AWS has 3 types of load balancers in ELB, which are
    • Application Load Balancers
    • Network Load Balancers
    • Classic Load Balancers
  • Application Load Balancer
    • Works on application layer or Layer 7
    • Protocols supported are – HTTP/1.1, and HTTP/2
    • Has WebSockets support
    • Supports routing of request like routing of HTTP requests based on path/headers
    • Used for offloading SSL/TLS
  • Network Load Balancer
    • Works on network layer or layer 4
    • Offers good routing performance like million request/second
    • Supports static IP
  • Classic Load Balancer
    • Is the legacy AWS load balancer
    • Works on layer 7 with support for layer 4 also
    • Layer 7 support limited to X-Forwarded
    • Protocols supported for layer 4 – TCP, TCP+SSL
    • Protocols supported for layer 7 – HTTP 1.1, HTTPS 1.1
  • Steps for enabling ELB
    • Define Load Balancer
    • Assign and configure Security Groups
    • Configure Health Check for load balancer
  • Add EC2 Instances
  • In Cross-Zone Load Balancing, traffic is distributed across target nodes in all enabled AZ
  • 504 error is given by ELB, when
    • no response
    • timeout
  • Target nodes can have 2 healthcheck status –
    • InService
    • OutOfService
  • Health check interval is time duration after which health check will take place
  • Default idle timeout value for classical and Application load balancer is 60 seconds
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