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Load Balancing Over Networks

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use of devices external to the processing nodes in a cluster ... No standard, but simular. General network traffic implementations. HolenTech HyperFlow ... – PowerPoint PPT presentation

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Title: Load Balancing Over Networks


1
Load Balancing Over Networks
  • Rawn Shah, Sun World Magazine
  • 2000. 3. 27. ???

2
Contents
  • Introduction
  • Balancing methods
  • Factors affecting balancing methods
  • Simple balancing methods
  • Advanced balancing methods
  • Common errors
  • Practical implementations
  • Summary

3
Introduction
  • Load balancing over a network
  • distribute workload or network traffic load
    across the cluster
  • use of devices external to the processing nodes
    in a cluster
  • Balancing devices
  • monitor the status of all processing node
  • use one or more algorithms and methods(static or
    dynamic)
  • Considerations of load balancing
  • network point of view Vs. application point of
    view
  • a data packet segmented packet
  • developed instead of QoS

4
Factors Affecting Balancing Methods(1/2)
  • NAT(Network address translator)
  • convert internal address and external address
  • cannot be used with VPN(Virtual Private Networks)
  • DNS(Domain name system) server
  • mapping FQDN(Fully Qualified Domain Name) to IP
    address
  • map multiple hosts to a single host name
  • Wire-speed processing
  • traffic bottlenecks at the network device or OS
    capacity
  • Node operating system limitations
  • large number of interrupts

5
Factors Affecting Balancing Methods(2/2)
  • Balancing device limitations
  • device tables limit the size of cluster and the
    traffic rate
  • Session- and nonsession-based traffic
  • session management in TCP packets
  • time interval-based UDP session management
  • Application dependencies
  • continuous service in shared nothing cluster
  • application level requirement of balancing device

6
Simple Balancing Methods(1/2)
  • Weighting
  • different weights to the nodes of different
    capacities
  • Randomization
  • works good in identical node environment
  • Round-robin
  • limitations
  • no knowledge of nodes, address caching
  • Hashing
  • same source address will always get assigned to
    the same server

7
Simple Balancing Methods(2/2)
  • Least connections
  • keep track of all currently active connections
  • differ from actual amount of processing
  • Minimum misses
  • least number of incoming requests in its history
  • Fastest response
  • make little sense except heavy load down
  • useful in different network segments

8
Advanced Balancing Methods(1/3)
  • Network traffic-based balancing
  • monitoring of incoming traffic from different
    sources
  • distributing them accordingly to the nodes
  • Node traffic-based balancing
  • contact software agent on the node
  • monitoring of the status of the network buffers
  • Node Load-based balancing
  • software agent
  • CPU or system load in UNIX systems
  • various system load in Windows NT systems

9
Advanced Balancing Methods(2/3)
  • Load-balancing domain name resolution
  • load balancing occurs within the DSN server
  • simple most popular
  • best used in a cluster of like nodes with
    identical applications
  • Topology-based redirection
  • effective in several clusters deployed across a
    network
  • redirect traffic to the cluster nearest the
    client
  • hop count(static)
  • network latency(dynamic)
  • fastest response
  • a top level node in a particular domain

10
Advanced Balancing Methods(3/3)
  • Policy-based redirection
  • mathematical or functional set of rules of
    balancing behavior
  • bandwidth allocation policies
  • higher priority on network administration
    security contorol
  • administrative policies
  • specific to the needs of each message in network
    environment
  • security policies
  • proper access right for access the resource
  • Application-specific redirection
  • support for application level of sessions
  • database Web load-balancing

11
Common Errors
  • Overflow
  • too much traffic to process
  • Underflow
  • one node is not getting enough traffic as other
    nodes
  • underutilized or starved
  • Routing errors
  • misconfiguration or a disconnected link
  • Induced network errors
  • too much traffic can appear as errors

12
Practical Implementations
  • No standard, but simular
  • General network traffic implementations
  • HolenTech HyperFlow
  • load balancing at the IP network level
  • independent of the TCP and UDP
  • not be functionally useful or efficient as
    balancing TCP sessions
  • weighting round-robin in initial load balancing
  • two level hashing as the basic method for mapping
  • one-to-one, many-source-to-one
  • multiple balancing devices

13
Practical Implementations
  • General network traffic implementations
  • Cisco LocalDirector
  • LAN-based system originally based on NAT
  • CIP(Channel interface processor)
  • 80Mbps, 700,000 TCP connections, 8,000 IP map in
    1997
  • 400Mbps, 1,000,000 TCP connections, 64,000 IP map
    now
  • Cisco DistibutedDirector
  • WAN-based system based on DNS
  • topology-based redirection
  • UDP-based Director Response Protocol(DRP)

14
Practical Implementations
  • General network traffic implementations
  • Resonate Central Dispatch
  • Primary scheduler communicates with the agent to
    determine server and network traffic load
  • Resonate Global Dispatch
  • Topology-based Redirection server that works with
    RCD
  • Alteon Networks ACEdirector
  • 10 or 100 Mbps Ethernet switches with load
    balancing
  • F5 Labs BIG/ip and 3DNS
  • Load balancing, DNS, firewall

15
Practical Implementations
  • Web-specific implementations
  • HydraWEB Load Manager
  • Web content level clustering
  • Portions of URL may be distributed across several
    nodes for asymmetric balancing
  • agents on nodes to monitor
  • RND Network Web Server Director and Director Pro
  • LAN-based cluster WSN, WSN Pro
  • WSN-DS (Distributed Sites) for distributed
    environment
  • dynamically reassigns nodes from other clusters
    to become part of the loaded system

16
Practical Implementations
  • Other application specific implementation
  • Sun Microsystems StorEdge
  • expansion of RAID to two-node cluster
  • remote mirroring (replication)
  • high-bandwidth direct connection between the two
    end-points
  • Check Point FireWall-1
  • network access security monitors or firewalls
  • Check Point VPN-1
  • IP-gateway providing certificate-based
    authentication
  • Check Point FloodGate-1
  • bandwidth can be assignment via domain names, IP
    address, or user information

17
Summary
  • Separate balancing device
  • in a network load balancing system
  • monitor traffic
  • execute a method of distributing traffic to a
    cluster of nodes
  • Balancing methods
  • implemented independently, but very similar
  • DNS as a crucial part in many load-balancing
    method
  • Network layer(IP) transport layer(TCP,UDP)
    implementation
  • Instead of QoS, best-guess and proprietary method
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