Load balancing is a key concept in distributed computing, that is critically crucial for ensuring effective distribution of network traffic to multiple servers, thereby avoiding overloading of any single server.

Load balancers like the Amazon Web Service’s (AWS) Application Load Balancer (ALB) serve to distribute incoming application traffic across multiple targets (in the form of EC2 instances), zones, or IP addresses. This helps enhance the scalability, availability, reliability, and redundancy of the applications.

Let’s delve deeper into the core concepts of Load Balancing, specifically in AWS context for the AWS Certified Solutions Architect – Associate (SAA-C03) exam.

Table of Contents

II. Types of Load Balancers in AWS

When it comes to AWS, we’ve three types of Elastic Load Balancers, each with a definitive set of capabilities:

  1. Classic Load Balancer (CLB)
  2. Network Load Balancer (NLB)
  3. Application Load Balancer (ALB)
Load Balancer Layer it Operates Usability
Classic Layer 4 and 7 Basic Load Balancing across multiple EC2 instances
Network Layer 4 Ideal for handling volatile network traffic
Application Layer 7 Best-suited for HTTP/HTTPS traffic across microservices and containers

III. Application Load Balancer (ALB)

An ALB functions at the application layer (the seventh layer of OSI model), which allows it to route traffic to targets based on the content of the request. This sophisticated load balancing makes ALBs perfectly suited for modern microservices architecture and container-based applications.

Core Concepts of ALB:

  1. Routing: Routes client requests to the appropriate target groups.
  2. Listener: Checks for connection requests from clients based on the protocol and port specified.
  3. Target Groups: Serves as a logical grouping of targets, such as EC2 instances.

IV. Load Balancing Algorithms

Load balancers employ different methods to distribute workload. Typically, AWS ALB uses the round robin algorithm by default. However, it can add a more sophisticated algorithm, known as ‘least outstanding requests’, which send requests to the server with the fewest pending requests.

V. Health Checks

ALBs conduct health checks on EC2 instances. If an instance fails health checks, ALB stops sending traffic to the failing instances, maintaining the robustness of the system.

VI. Benefits of Application Load Balancer

  1. Improved Performance: By distributing the workload, ALB ensures no single server is overwhelmed, thereby improving the application’s overall performance.
  2. Scalability: You can quickly scale your resources up or down based on the application demand, making ALB a cost-effective solution.
  3. High Availability: By distributing the load across multiple servers and zones, ALB ensures high application availability, even if a server or zone goes down.
  4. Security: ALBs offer built-in security features to protect your applications from common threats.

In conclusion, understanding load balancing, especially in the frame of ALBs, is integral for any solutions architect or developer dealing with AWS. From enhancing application performance to ensuring high availability and security, the strategic implementation of Application Load Balancers can greatly optimize your AWS architecture.

Practice Test

True or False? An Application Load Balancer functions at the network level.

  • True
  • False

Answer: False

Explanation: Application Load Balancer functions at the application level, the seventh level of the OSI model.

Which type of Amazon ELB is best suited for load balancing of HTTP and HTTPS traffic and operates at Layer 7 of the OSI model?

  • A) Network Load Balancer
  • B) Application Load Balancer
  • C) Classic Load Balancer
  • D) None of the Above

Answer: B) Application Load Balancer

Explanation: Application Load Balancer is designed to handle HTTP and HTTPS traffic and operates at the seventh layer of the OSI model.

An Application Load Balancer supports path-based routing.

  • True
  • False

Answer: True

Explanation: An Application Load Balancer supports path-based routing and can route requests to different backend services based on the URL path.

Which ELB option cannot handle millions of requests per second?

  • A) Network Load Balancer
  • B) Application Load Balancer
  • C) Classic Load Balancer

Answer: C) Classic Load Balancer

Explanation: Network and Application Load Balancers can handle millions of requests per second, while Classic Load Balancer cannot.

Can you disable cross-zone load balancing in AWS?

  • A) Yes
  • B) No

Answer: A) Yes

Explanation: By default, cross-zone load balancing is enabled in Application Load Balancer. However, it can be disabled if not required.

True or False? Sticky sessions are supported by Application Load Balancer.

  • True
  • False

Answer: True

Explanation: The sticky sessions feature of Application Load Balancer enables the load balancer to bind a user’s session to a specific target.

Which type of routing algorithm is used by Application Load Balancer?

  • A) Round Robin
  • B) Least Connections
  • C) IP Hash

Answer: A) Round Robin

Explanation: Application Load Balancer uses the Round Robin routing algorithm.

In which of the following cases would Application Load Balancer be the most efficient choice?

  • A) When you need to balance the load of static files
  • B) When you want to direct the web traffic to multiple services
  • C) When you want to balance the TCP traffic

Answer: B) When you want to direct the web traffic to multiple services

Explanation: Application Load Balancer is highly efficient in directing web traffic to multiple backends.

True or False? AWS Application Load Balancer cannot route traffic to multiple ports on a single EC2 instance.

  • True
  • False

Answer: False

Explanation: AWS Application Load Balancer can route traffic to multiple ports on a single EC2 instance, offering flexibility in managing multiple microservices on the same EC2 instance.

In terms of Application Load Balancer, what does connection draining refer to?

  • A) Terminating a session once it is inactive
  • B) The loss of data during load balancing
  • C) It drains all the connection attempts if they exceed a certain limit
  • D) It reroutes traffic from instances that will be deregistered

Answer: D) It reroutes traffic from instances that will be deregistered

Explanation: Connection Draining is a process that reroutes new traffic from instances that are failing or are being updated or deregistered, allowing existing connections to complete.

Can an Application Load Balancer be associated with more than one security group?

  • A) Yes
  • B) No

Answer: B) No

Explanation: No, an Application Load Balancer can only be associated with a single security group, unlike EC2 instances which can be associated with multiple security groups.

Which of the following services does an Application Load Balancer natively integrate with?

  • A) AWS Auto Scaling
  • B) Amazon ECS
  • C) AWS CodeDeploy
  • D) All of the above

Answer: D) All of the above

Explanation: AWS Application Load Balancer natively integrates with several AWS services such as AWS Auto Scaling, Amazon ECS, AWS CodeDeploy etc.

In context of AWS, can an instance be registered with more than one load balancer at once?

  • A) Yes
  • B) No

Answer: A) Yes

Explanation: Yes, an instance can be registered with more than one load balancer at the same time.

Can an Application Load Balancer direct traffic based on the content of the request?

  • A) Yes
  • B) No

Answer: A) Yes

Explanation: Application Load Balancer can direct traffic based on the content of the request, making it highly specialized and efficient.

True or False? Application Load Balancer cannot handle sudden and unpredictable traffic patterns.

  • True
  • False

Answer: False

Explanation: Application Load Balancer is designed to handle sudden and unpredictable traffic patterns while seamlessly scaling to accommodate larger loads.

Interview Questions

What is an Application Load Balancer in AWS?

The Application Load Balancer is a fully managed service provided by AWS that automatically distributes incoming application traffic across multiple targets, such as Amazon EC2 instances, containers, and IP addresses, in a single Availability Zone or multiple Availability Zones.

How does AWS Application Load Balancer work?

Application Load Balancer operates at the request level (layer 7), routing traffic to targets within Amazon VPC based on the content of the request.

What are the key features of the Application Load Balancer?

Some of the key features are: HTTP/HTTPS routing, host and path-based routing, service containers support, health checks to ensure traffic only goes to healthy targets, and integration with other AWS services such as EC2 Auto Scaling, AWS Certificate Manager, AWS Config, among others.

What are the types of load balancers AWS provides?

AWS provides three types of load balancers: Application Load Balancer, Network Load Balancer, and Classic Load Balancer, each tailored to specific application or transport layer traffic.

In what scenarios should you use an Application Load Balancer?

Application Load Balancer is best suited for load balancing of HTTP and HTTPS traffic and provides advanced request routing targeted at the delivery of modern application architectures, including microservices and containers.

Can an Application Load Balancer distribute traffic to multiple ports on the same EC2 instance?

Yes, Application Load Balancer allows you to register targets in target groups using a protocol and port number, allowing for traffic distribution to multiple ports on the same EC2 instance.

What is a target group in the context of Application Load Balancer?

A target group is used to route requests to one or more registered targets when using an Application Load Balancer. Health checks are configured in target groups and can be used to check the health of all targets registered with a target group.

How does Application Load Balancer improve the performance of applications?

By distributing incoming application traffic across multiple targets, Application Load Balancer can ensure that no single server carries too much load. This can increase the overall speed of the application by preventing any one target from being a bottleneck.

How does Session Stickiness work with the Application Load Balancer?

Session stickiness enables the load balancer to bind a user’s session to a specific instance. The load balancer uses a special cookie to associate the session with the original server, which can be configured for any duration.

What is the difference between an Application Load Balancer and a Network Load Balancer?

A Network Load Balancer operates at the transport layer (Layer 4) and routes traffic based on IP protocol data. An Application Load Balancer operates at the Application layer (Layer 7) and makes routing decisions at the application level that allow it to route requests to different services based on the content of the request.

Since AWS provides health checks, how does Application Load Balancer deal with unhealthy instances?

If an instance fails a health check, the Application Load Balancer stops sending traffic to that instance and spreads the load across the remaining healthy instances.

How is an Application Load Balancer different from a Classic Load Balancer?

The Classic Load Balancer operates at both the request level and connection level, whereas Application Load Balancer routes traffic based on content of the request (Layer 7). Additionally, Application Load Balancer supports HTTP/2 and WebSocket, which are not supported by the Classic Load Balancer.

Can Application Load Balancer route requests to Lambda functions?

Yes, with the Application Load Balancer’s support for a Lambda function as a target, clients can directly invoke a Lambda function through HTTP(S) request.

Are there any limits to the number of rules that can be added to an Application Load Balancer?

Yes, by default, you can add up to 100 rules to each of your Application Load Balancer.

Does Application Load Balancer support IPv6?

Yes, AWS Application Load Balancer supports both IPv4 and IPv6 addresses for client and back-end connections.

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