Concepts
The primary purpose of a load balancer is to distribute incoming network traffic across a group of backend servers, known as a server pool or server farm. This distribution ensures that no single server bears too much demand.
High Availability
One of the key purposes of a load balancer is to improve the availability of applications by routing traffic only to the healthy instances. If one instance fails, the load balancer will stop sending traffic to it and reroute the traffic to other operational instances.
Traffic Distribution
Load balancers can distribute the traffic based on various algorithms, including round-robin, IP-hash, or least connections. This distribution ensures that workloads are handled effectively and that no single instance is overwhelmed, which can lead to degraded performance or failures.
Scalability
As traffic to an application grows, load balancers facilitate straightforward horizontal scaling. New instances can be added to the pool, and the load balancer will start incorporating them into the rotation without any need for manual redistribution of traffic.
Redundancy
Load balancers can provide redundancy by ensuring that if one instance becomes unavailable, the others can still handle the incoming traffic. This can be crucial for maintaining uptime during maintenance or in the event of unexpected failures.
Health Checks
Load balancers perform health checks on instances to ensure traffic is only sent to those that are responding correctly. If an instance does not pass a health check, it is temporarily removed from the pool until it is healthy again.
SSL Termination
Load balancers can terminate SSL connections at the load balancer level, offloading the SSL decryption work from the actual servers that host the applications. This can improve the performance of the servers by reducing their processing load.
Session Persistence
Sometimes, it is necessary to maintain a user’s session on a single server for the duration of their visit. Load balancers can ensure session persistence (also known as sticky sessions) by directing a user’s session to the same server each time.
AWS offers several types of load balancers that suit different use cases:
Application Load Balancers (ALBs)
Application Load Balancers are best suited for HTTP and HTTPS traffic. They can route traffic to services based on the content of the request. For example, they could send requests for a specific URL to one set of instances and requests for a different URL to another.
Network Load Balancers (NLBs)
Network Load Balancers handle TCP traffic where extreme performance is required. They are capable of handling millions of requests per second while maintaining ultra-low latencies.
Classic Load Balancers (CLBs)
Classic Load Balancers are the legacy option for applications that were built within the EC2-Classic network. They provide basic load balancing at both the request level and the connection level.
| Feature | Application Load Balancer | Network Load Balancer | Classic Load Balancer |
|---|---|---|---|
| Supported Protocols | HTTP, HTTPS | TCP, TLS | HTTP, HTTPS, TCP, SSL |
| Performance | High | Highest | Moderate |
| Routing based on content | Yes | No | No |
| WebSocket and HTTP/2 | Yes | No | No |
| SSL Termination | Yes | Yes | Yes |
| Fixed Hostname | Yes | Yes | No |
In conclusion, load balancers serve to distribute network traffic across multiple servers to ensure high availability, better fault tolerance, scalability, and an efficient user experience. AWS Certified Cloud Practitioner (CLF-C02) candidates must understand the basic functionality and use cases of each type of load balancer offered by AWS to effectively design and manage load balancing for their applications.
Answer the Questions in Comment Section
True or False: A primary purpose of a load balancer is to distribute traffic across multiple computing resources to prevent overload on any single resource.
- (A) True
- (B) False
Answer: A
Explanation: True, load balancers distribute incoming network traffic across multiple servers to ensure no single server bears too much load.
Which AWS service is primarily used for distributing traffic across multiple Amazon EC2 instances?
- (A) Amazon Route 53
- (B) AWS Lambda
- (C) Amazon Elastic Load Balancing (ELB)
- (D) Amazon S3
Answer: C
Explanation: Amazon Elastic Load Balancing (ELB) automatically distributes incoming application traffic across multiple targets, like Amazon EC2 instances.
Load balancers only operate at Layer 4 (transport layer) of the OSI model.
- (A) True
- (B) False
Answer: B
Explanation: Load balancers can operate at both Layer 4 (transport layer, e.g., TCP/UDP) and Layer 7 (application layer, e.g., HTTP/S) of the OSI model.
Which of the following is NOT a function of a load balancer?
- (A) Distributing traffic to prevent server overload
- (B) Encrypting data at rest
- (C) Ensuring high availability and fault tolerance
- (D) Providing SSL termination
Answer: B
Explanation: Encrypting data at rest is not a function of a load balancer; it’s typically handled by storage services or specific encryption tools.
True or False: Elastic Load Balancing supports health checks to automatically reroute traffic from unhealthy instances to healthy ones.
- (A) True
- (B) False
Answer: A
Explanation: True, health checks are used by ELB to route traffic away from failed instances to those that are healthy.
In AWS, which of the following types of load balancers allows you to route based on URL path?
- (A) Classic Load Balancer (CLB)
- (B) Network Load Balancer (NLB)
- (C) Application Load Balancer (ALB)
- (D) All of the above
Answer: C
Explanation: Application Load Balancer (ALB) supports advanced request routing, such as routing based on URL paths.
True or False: A load balancer can serve as a single point of failure (SPOF) in your architecture.
- (A) True
- (B) False
Answer: B
Explanation: False, one of the key purposes of a load balancer is to increase availability and prevent a single point of failure. They are typically built for high availability and redundancy.
Load balancers can provide SSL/TLS decryption, reducing the encryption overhead on the actual servers.
- (A) True
- (B) False
Answer: A
Explanation: True, load balancers can offload SSL/TLS decryption, which can reduce load on backend servers.
What is the term used for balancing loads across different geographical regions?
- (A) Horizontal Scaling
- (B) Vertical Scaling
- (C) Global Load Balancing
- (D) Cross-Zone Load Balancing
Answer: C
Explanation: Global Load Balancing typically refers to distributing traffic across servers in multiple geographic regions.
AWS Elastic Load Balancing automatically scales its request handling capacity in response to incoming traffic.
- (A) True
- (B) False
Answer: A
Explanation: True, AWS Elastic Load Balancing scales its resources automatically to adapt to varying traffic loads.
Sticky sessions can be useful when you need to:
- (A) Encrypt data at rest
- (B) Maintain a user’s session on a specific server
- (C) Improve SSL/TLS performance
- (D) Reduce latency by routing traffic to the nearest data center
Answer: B
Explanation: Sticky sessions enable the load balancer to bind a user’s session to a specific EC2 instance, which is helpful for maintaining session state.
Network Load Balancers are best suited for:
- (A) High throughput, low latency TCP traffic
- (B) Layer 7 traffic routing based on content
- (C) Encrypting and decrypting data at rest
- (D) Redirecting HTTP to HTTPS automatically
Answer: A
Explanation: Network Load Balancers are optimized for handling high throughput, low latency TCP traffic, where performance is critical.
Excellent post on load balancers! It clearly explained the purpose and benefits.
This article helped me understand how load balancers improve availability and reliability.
I appreciate the detailed explanation of different types of load balancers.
One of the key purposes of load balancers is to distribute network or application traffic across multiple servers. This ensures no single server bears too much load.
Thanks for this post! It clarified my doubts about load balancers
I think the explanation of session persistence in load balancers was a bit too brief.
Another purpose of load balancers is to enhance the performance of applications by scaling them horizontally.
Thanks for the informative post!