Net330:Server‐Load‐Balancing - ConnorEast/Tech-Journal GitHub Wiki

Definitions

RAID [Redundant Array of Independent Devices]:
SLB [Server Load Balancing]:
VIP [Virtual Server / Front End]: A term created to specify a website
Zoning: Network segmentation to reduce backend exposed attack surfaces
F5/NetScaler: The two most popular vendors for SLB Software and Devices.
NGINX/HAProxy: Open-source software based Load Balancer's

Load-Balancing Concepts

Load balancing is the distribution of workload across multiple computing resources to increase Efficiency, Performance, Availability [Redundancy], Elasticity [Growth], and Security [Zoning]. Load balancing can include network links, computer/servers, cpu's, and disk drives.

Network VS Server/Service Load Balancing

Load-Balancers are pieces of hardware focused on communication distribution Many Load-Balancers provide ssl/tls "offload" while handling cryptographic functions and communication to the back end servers.

Network Load Balancing	Server Load Balancing
Balance Traffic across network links Handled with routing and other protocols provides redundancy Provides link selection based on criteria (Bandwidth, Load, Cost $)	Provides a single service using multiple servers on the back end Highly customizable and widely-used in modern enterprises Performance, Security, Elasticity, Redundancy all popular reasons

Layer 3 SLB

Layer 3 SLB's work with IP addresses. They only use the IP addresses of different servers

DNS RoundRobin is an example of Layer 3 SLB

Multiple A records for same hostname
Queries yield different answers so different servers are contacted
Do an nslookup on google.com. You should get different IP's then your neighbor.

Layer 4 SLB

TCP/UDP ports operate at layer 4
Layer 4 SLB's use dedicated load balancers
Load balancers host "virtual IPs"(aka front-end) with the ip and port that end user uses to access a server
The load-Balancer than broker the connection with a server in the "backend"

Layer 7 SLB

Does a full-packet inspection to parse URL's and or Headers/Content-Metadata
Can be used to create a sacrificial lamb server [Specifically against DoS] to improve the reliability and security of internal systems.

SLB Service Monitoring

Load-Balancers can also monitor servers/services to make sure they are running. If a server/service has been found to have gone done it will be removed from the pool.

This monitoring (aka health checks) can include:

Simple IP, TCP, or UDP connectivity
Particular Protocol Response (SMTP, HTTP, FTP...)
Presence of a certain resource (web page) or successful completion of a transaction

Load Balancing Issues

Issue 1: The backend server will not be able to gain information to that of the IP address of the source of a packet due to the fact that the source IP is changed to that of the load balancer. This causes issues for troubleshooting & incident response

Fix:

For HTTP: -create the X-Forwarded-For header that adds the original source IP to the request.
For other protocols: - need extensive logging on the Load Balancer that correlates with the backend server logs. [Use Splunk]

Issue 2: Some applications require servers to store information for the user. If user is directed to other servers that information may be lost.