Section - Elastic Load balancer

Question 1

What is AWS Elastic Load Balancer?

Answer 1

• Elastic Load balancing automatically distributes incoming application traffic across multiple targets, such as Amazon EC2 instances. This can be done across mutliple AZs.
• 3 Different types of Load Balancers:
  
  • Application Load Balancer
    
    • Best suited for load balancing HTTP and HTTPS traffic.
    • They operate at Layer 7 and are application-aware
    • Intelligent Load Balancer
  • Network Load Balancer
    
    • Operating at the connection level (Layer 4)
    • Capable of handling millions of requests per second, while maintaining ultra-low latencies.
    • Performance Load balancer
  • Classic Load Balancer
    
    • Legacy load balancers
    • You can load balance HTTP/HTTPS application and use Layer 7 specific features, such as X-Forwarded and sticky sessions.
    • Classic/Test/Dev Load Balancers.

Question 2

What is Health Checks?

Answer 2

• All AWS load balancers can be configured with health checks. Health checks periodically send requests to load balancers’ registered instances to test their status.
• The status of any instances that are unhealthy at the time of the health check is OutOfService.
• The load balancer performs health checks on all registered instances, whether the instance is in a healthy state or unhealthy state.
• The load balancer routes requests only to the healthy instances. when the load balancer determines an instance is unhealthy, it stops routing requests to that instance.

Question 3

Application Load balancer (Layer 7)?

Answer 3

• An Application Load Balancer functions at the Application layer - The 7th layer of the OSI Model
• After the load balancer receives a request, it evaluates the listener rules in priority order to determine which rule to apply, and the selects a target from the target group for the rule action.
• Limitations: application load balancers only support HTTP and HTTPS
• To use an HTTPS listener, you must deploy at least one SSL/TLS server certificate on your load balancer. The load balancer uses a server certificate to terminate the frontend connection and then decrypt requests from clients before sending them to the targets.

Question 4

What is Path-Based Routing?

Answer 4

Question 5

What is Layer 4 Network load Balancer?

Answer 5

• A network load balancer functions at the fourth layer of the open systems interconnection (OSI) model. it can handle millions of requests per second.
• Requests Recieved: after the load balancer recieves a connection requests, it selects a target from the target group for default rule.
• It attempts to open a TCP connection on the selected target on the port specified in the listener configuration.
• A Listener checks for connection requests from clients, using the protocol and port you configure. The listener on a Network Load balancer then forwards the request to the target group. There are NO RULES, unlike with Application Load Balancers.
• Supported Ports and Protocols:
  
  • Ports: 1 - 65535
  • Protocols: TCP, UDP,TLS,TCP_UDP
• You can use a TLS listener to offload the work of encryption and decryption to your load balancer so your applications can focus on their business logic.
• If the listener protocol is TLS, you must deploy exactly one SSL server certificate on the listener.

Question 6

What is Classic Load balancer?

Answer 6

• Classic Load balancer are the legacy load balancers.
• You can load balance HTTP/HHTPS applications and use Layer 7 - specific features, such as X-Forwarded and Sticky sessions.
• You can also use strict Layer 4 load balancing for applicaitons that relay purely on the TCP Protocol
• X-Forwarded-For
  
  • When traffic is sent from a load balancer, the server access logs contain the IP address of the proxy or load Balancer only
  • To see the original IP address of the client, the X-Forwarded-For request header is used.
• HTTP 504 error means the gateway has timed out, the application downstream is no responding within the idle timeout period.

Question 7

What are Sticky Sessions?

Answer 7

• Classic Load Balancer route each request independently to the registered EC2 instance with the smallest load.
• Sticky sessions allow you to bind a user’s session to a specific EC2 instance.
• Stick session ensures all requests from the user during the session are sent to the same instance.
• Application Load balancers support the use of Sticky Sessions. but the traffic will be sent at the target group level.
• If Sticky session are in use an EC2 instance goes down, you can disable sticky session to prevent the load balancer from sending request to EC2 which is down.

Question 8

What is Deregistration Delay(Connection Draining)?

Answer 8

• Deregistration delay allows Load balancers to keep existing connections open if the EC2 instances are de-registered or become unhealthy.
• This enables the load balancer to complete in-flight requests made to instances that are de-registering or unhealthy.
• NB: you can disable deregistration delay if you want your load balancer to immediately close connections to the instances that are de-registering or have become unhealthy.