What is ELB?
Elastic Load Balancing automatically distributes incoming application traffic across multiple targets, such as Amazon EC2 instances. This can be done across multiple AZs.
What are the 4 different types of ELB in AWS.
- Application Load Balancer
- Network Load Balancer
- Gateway Load Balancer
- Classic Load Balancer
Describe ALB.
Application Load Balancer:
- Best suited for load balancing of HTTP and HTTPS traffic.
- They operate at Layer 7 and are application-aware.
- Intelligent Load Balancer
Describe NLB.
Network Load Balancer
- Operating at the connection level (Layer4)
Network Load Balancers are capable of handling millions of requests per
second, while maintaining ultra-low latencies.
- Performance Load Balancer
Describe CLB.
- Classic Load Balancers are the legacy load balancers. You can load balance HTTP/HTTPS applications and use Layer 7-specific features, such as X-Forwarded-For and sticky sessions.
- You can also use strict Layer 4 load balancing for applications that rely purely on the TCP protocol.
Classic/Test/Dev Load Balancer.
LB and health checks.
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 the instances that are healthy at the time of the health check is InService.
- 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 an unhealthy state.
Describe Gateway Load Balancer
Choose a Gateway Load Balancer when you need to deploy and manage a fleet of third-party virtual appliances that support GENEVE. These appliances enable you to improve security, compliance, and policy controls.
What are the listeners in ALB?
- A listener checks for connection requests from clients, using the protocol and port you configure.
- You define rules that determine how the load balancer routes requests to its registered targets.
- Each rule consists of a priority, one or more actions, and one or more conditions.
How does Elastic Load Balancing work?
- Clients make requests to your application.
- The listeners in your load balancer receive requests matching the protocol and port that you configure.
- The receiving listener evaluates the incoming request against the rules you specify, and if applicable, routes the request to the appropriate target group. You can use an HTTPS listener to offload the work of TLS encryption and decryption to your load balancer.
- Healthy targets in one or more target groups receive traffic based on the load balancing algorithm, and the routing rules you specify in the listener.
What are the target groups in ALB?
Each target group routes requests to one or more registered targets, such as EC2 instances, using the protocol and port number you specify.
What are the Limitations of ALB?
- 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.
What are the listeners in NLB?
- 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.
What is a TLS listener in NLB?
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.
What are some use cases of NLB?
- Network Load Balancers are best suited for load balancing of TCP traffic
where extreme performance is required. - Operating at the connection level (Layer 4, Network Load Balancers are capable of handling millions of requests per second, while maintaining ultra-low latencies.
- Use for extreme performance!
How the X-Forwarded-For request header is used in CLB?
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.
What are the Gateway Timeouts in CLB?
If your application stops responding, the Classic Load Balancer responds with a 504 error.
This means the application is having issues. This could be either at the web server layer or the database layer.
What Are Sticky Sessions?
Classic Load Balancers 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.
- You can enable sticky sessions for Application Load Balancers as well,
but the traffic will be sent at the target group level.
What Is Deregistration Delay?
- Deregistration delay allows load balancers to keep existing connections open if the EC2 instances are deregistered or become unhealthy.
- This enables the load balancer to complete in-flight requests made to instances that are deregistering or unhealthy.
- You can disable deregistration delay if you want your load balancer to immediately close connections to the instances that are deregistering or
have become unhealthy
What are the main differences between Internet-Facing Load Balancers (ILBs) and Internal Load Balancers (ILBs) in AWS?
- Internet-Facing Load Balancers (ILBs) are accessible from the internet and distribute traffic from clients on the public internet. They have nodes in public subnets and public IPv4.
- Internal Load Balancers (ILBs) are not accessible from the internet and are used for distributing traffic within a Virtual Private Cloud (VPC). They have nodes in private subnets and private IPv4.
- Internet-facing ILBs have a publicly resolvable DNS name, while Internal ILBs have a DNS name resolvable only within the VPC.
What is the recommended minimum subnet size for Amazon Elastic Load Balancers (ELBs) in AWS?
- The recommended minimum subnet size for ELBs is /27 or larger. A /27 subnet provides 32 IP addresses, with 27 available for use, allowing for better flexibility and scalability.
- While a “/28”(leaves 11 free, aws says at least 8 free needed) subnet might technically meet the minimum requirement for ELB operation, it doesn’t leave much room for expansion or flexibility.
What is the minimum number of Availability Zones required for an Amazon Elastic Load Balancer (ELB) in AWS?
The minimum number of Availability Zones required for an ELB in AWS is Two. Multi-AZ configuration ensures high availability and fault tolerance.
What is Cross-Zone Load Balancing in AWS?
- Cross-Zone Load Balancing evenly distributes traffic across instances in all enabled Availability Zones, enhancing load balancing efficiency.
- It’s a default feature in for Application Load Balancers (ALBs) (only?).
- It promotes high availability by ensuring that all instances in different AZs participate in handling requests.
What limitation is associated with Classic Load Balancers (CLBs) in AWS for handling HTTPS traffic with multiple domains?
- SNI Support: CLBs do not support Server Name Indication (SNI), which is essential for handling multiple SSL certificates on a single load balancer.
- Scaling Flexibility: As a result, each unique domain with a different SSL certificate requires a separate CLB, limiting scaling flexibility and potentially increasing operational complexity.
Can ALBs and NLBs in AWS have static IP addresses?
- ALBs do not have static IP addresses and rely on DNS names for routing.
- NLBs can have static Elastic IP addresses (EIPs) associated with them, providing a fixed entry point for clients.
