Elastic load balancer

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ELB Icon

Introduction

• Elastic load balancer is a managed service which can spread load across multiple services.

• It is a regional service, making them highly available.

• Exposes a single point of access for DNS to your application.

• AWS takes care of the infra and upgrades of load balancers.

• Provides SSL termination for your websites.

• Offers health checks (health endpoints), to make sure the requests are forwarded only to health instances.

• Can be setup as public or private load balancer depending on the scheme.

• Provides high availability across zones.

• Can enforce stickiness with cookies.

Target groups

• In general, group of AWS resources which would receive traffic from load balancer.

• Allows grouping of

  • EC2 instances

  • ECS tasks

  • IP addresses (must be private)

  • Lambda function

  • Application load balancer

• Read more about it here.

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 its registered targets.

• Read more about it here.

Health Checks

• To enable load balancer to know if the instance is healthy and can forward traffic to it, health checks play crucial role.

• Health check is done using /health endpoint (typically) running on port 4567 using http protocol.

• They are done at target group level.

• Health checks need to be configured when creating a target group before registering targets in to the target group.

Types of Load Balancer

Classic Load Balancer (CLB)

• Deprecated and retired, old generation (v1).

• Supports HTTP, HTTPS, TCP, SSL.

• Only supported one SSL certificate for HTTPS based listeners.

Application Load Balancer (ALB)

• Newer generation, 2016.

• Works on layer 7 of OSI model, supports HTTP/1.x, HTTP/2 HTTPS, WebSocket, gRPC.

• Supports redirect from HTTP to HTTPS.

• Great fit for microservices and container-based application.

• Supports routing to different target groups based on,

  • Path in URL

  • Hostname in URL

  • Query strings and headers

• Port mapping feature allow to redirect to a dynamic port in ECS.

• The IP address of the client is available in the header X-Forwarded-For, the port of the client in header X-Forwarded-Port, the protocol in header X-Forwarded-Proto.

• Target groups can be EC2 instances, ECS Task, Lambda functions (requests are translated to JSON event), Private IP Address.

• Health checks are done at target group level.

• ALB as has a fixed hostname of the form xxx.region.elb.amazonaws.com.

Network Load Balancer (NLB)

• Newer generation, 2017.

• Not available in free-tier option.

• Target groups can be EC2 instances, Private IP Addresses, ALB.

• Layer 4 load balancer, supports TCP, TLS, UDP.

• High performance, with ultra-lower latency.

• Has one static IP per AZ, with ability to assign elastic IP to each AZ.

• Health check supports TCP, HTTP and HTTPS.

Gateway Load Balancer (GWLB)

• Newer generation, introduced in 2020.

• Operates at network layer 3.

• Target groups can be EC2 instances, Private IP Addresses.

• Can be used to deploy, manage and scale a fleet of 3rd party virtual appliances which includes Firewalls, IDPS, Deep packet inspection etc.

• Uses GENEVE protocol at port 6081.

References

• Working of Load balancer

• ALB v/s NLB