Bai Viet Tap Chi Cong Nghe

7/30/2019 Bai Viet Tap Chi Cong Nghe

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Tn bi vit:

SDNG GII PHP LOAD BALANCING GIM TI CHO MY CH CUNG

CP DCH V

ThS. Hong STng KS: Cao Minh Tun

Hin nay, khi nhu cu truy cp mng

bng n, cc my ch cung cp dch vang

trnn qu ti. Vic la chn mt my ch

n l c cu hnh cc mnh p ng nhu

cu ny s ko theo chi ph u t rt ln.

Gii php hiu quc a ra l s dng

mt nhm my ch cng thc hin mt chc

nng di s iu khin ca mt cng c

phn phi ti - Gii php cn bng ti.

C rt nhiu hng a ra gii php

cn bng ti nh Cisco, Coyote Point, Sun

Microsystems... vi rt nhiu tnh nng

phong ph. Tuy nhin, v c bn, nguyn

tc cn bng ti vn xut pht t nhng quan

im k thut kh tng ng.

Nh vy ta c th thy c rng

hin nay c rt nhiu gii php cn bng ti

khc nhau. Ty thuc vo tnh bo mt, gi

thnh, chc nng chng ta yu cu m la

chn dng phng php no, phn cng hay

phn mm...Tuy nhin, c nhng gii php

dng phn cng hoc dng phn mm li c

gi thnh rt cao so vi quy m ca n v

s dng.

nh ngha cn bng tiLoad

Banlancing

Cn bng ti (Load Balancing) l

mt k thut phn phi khi lng cngvic mt cch ng u trn hai hoc nhiu

my tnh v cc vn lin kt mng, CPU,

cng, hoc cc ngun lc khc, c th

s dng ti nguyn mt cch ti u, ti a

ho thng lng, gim thiu thi gian hot

ng, v trnh tnh trng qu ti. S dng

nhiu dch v vi cn bng ti, thay v mt

dch v duy nht, c thlm tng tin cy

thng qua cc my d phng.

Trong , Network Load Balancing

l mt k thut nhm mrng hiu nng ca

cc my chng dng, chng hn nh Web

server, nhphn phi cc yu cu ca client

cho cc my ch trong nhm. Cc my

ch u nhn gi IP n, nhng gi ch

c x l bi mt my ch nht nh. Cc

my ch trong nhm s ng thi p ng

cc yu cu khc nhau ca cc my trm,

cho d mt my trm c th a ra nhiu

yu cu. Vi k thut cn bng ti, qu trnh


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x l v thi gian p ng my trm s

nhanh hn nhiu.

Chc nng ca cn bng ti

Mt cn bng tiLoad balancer c

nhng chc nng sau:

Chn lu lng mng (chng hn lulng web) n 1 trang web. Bn thn

thit b cn bng ti c th l mt Proxy,

mt Firewall tng ng dng (

Application Layer), n s l i tng

u tin nhn cc yu cu trc khi chia

ti, do , chc nng ny c coi nh

mt chc nng thit yu ca mt cnbng ti.

Tch cc lu lng thnh cc yu curing bit v quyt nh my ch no

nhn cc yu cu . y l chc nng

ch cht ca cn bng ti. Ty vo thut

ton p dng m s c tng cch phn

chia c th cho mi my.

Duy tr mt c ch nhng my chang sn sng, chc chc rng chng

ang p ng cc yu cu. Gia cn

bng ti v my ch lun phi c lin lc

vi nhau ( Keep Alive) bit c my

ch cn sng hay khng.

Cung cp khnng d phng bng cchs dng nhiu hn mt kch bn fail-

over.

Cung cp kh nng nhn thc ni dungphn tn bng cch c URL, chn

cookies, v bin dch XML. y c coi

nh l mt trong nhng tiu ch chia ti

ca h thng.

u im ca cn bng ti trong ng dng

thc t

Flexibility: Tnh linh hot cao. H

thng cho php b sung v loi b cc my

ch bt k lc no, v hiu qu l ngay lp

tc. Thc t vic ny khng lm nh hng

gin on ti hot ng ca c h thng, m

ch l mt node trong h thng . iu ny

cho php duy tr, sa cha bt k my

no, thm ch trong gi cao im vi tc

ng t hoc khng c tc ng no ti hthng. Mt cn bng ti (Load Balancer)

cng c th trc tip iu khin lu lng

mng bng cch s dng tp tin cookie,

phn tch c php URL, cc thut ton tnh

v ng, v nhiu hn na, tm ra cch

phn ti ti u cho h thng.

High availability: Tnh sn sng cao.

H thng s lin tc kim tra trng thi

(status) ca cc my ch trong h thng, t

ng loi bt k my ch no khng c tr

li v trong mt chu k, cng nh tng

thm my ch ngay khi hot ng trli.

iu ny l hon ton tng, thng qua c

ch giao tip ca cn bng ti v cc server,

khng cn c s tham gia iu khin trc

tip ca ngi qun tr (Administrator). Do

d, mt h thng cn bng ti hng n

tnh d tha, d phng cho thit b chnh

trong trng hp c thit bno bfail.


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Scalability: Kh nng m rng cao.

Cn bng ti chu trch nhim phn phi ti

ti nhiu ny server trong mt h thng

(Server Farm theo mt vt l, v c gi l

Server Clusercc b Server), vi mc ch

l nng cao hiu qu, tng sc mnh phc v

vi s lng ln cc my ch. iu ny

mang li li ch to ln v kinh t, v ch mt

chi ph cho nhiu my ch nh, thay v u

t cho mt my ch ln, thit b chuyn

dng. Ngoi ra, trong qu trnh hat ng,

cc my ch c th thay i, thm bt, loi

b, thay th mt cch d dng khng nhhng n hot ng ca h thng, gi cho

h thng lunHigh availability.

Cc thut ton Load Balancing

Hin nay, thut ton c s dng

ph bin l thut ton Weighted Round

Robin (WRR). Thut ton ny iu phi cc

real server cng lun phin ging Round-

Robin nhng n cn kt hp vo khnng

x l ca tng my server (Round -

Robin xem nh khnng x l tt c server

bng nhau). Mi server c nh gi

bng mt s integer (gi tr Weight) ch ra

kh nng x l ca n. Mc nh gi

tr Weight bng 1. V d ,

cc realserver A, B, C c weight ln lt

l 4, 3, 2 v th tiu phi cc yu cu

AABABCABC, n lun phin trong chu k

(mod sum(Wi)). Th t chn real server

phc v da vo s Weight ca server.

Trong WRR, cc realserver c gi

tr weight cao s nhn c kt ni mi

u tin v nhn nhiu kt ni hn server c

weight thp, servers c gi tr weight bng

nhau s nhn s phn ti cc kt ni mi

bng nhau.

Ngoi thut ton Weighted Round Robin cn

mt s thut ton sau:

Round Robin. Least Connection Weighted Least Connection

Cc k thut sdng trong cn bng ti

K thut c s dng ph bin lk thut Linux Virtual Server - Network

Address Translation ( NAT ).

Kin trc LVS-NAT c m tnh hnh

sau:

Hot ng ca LVS-NAT nh sau:

khi 1 user truy cp vo virtual service c


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cung cp bi cluster server, mt

request packet c gi n virtual IP

address (IP chp nhn yu cu cho Virtual

service) n Load balancer.

Load balancer xc nh a chch v port

number ca packet nu n hp l vi virtual

service c cung cp bi cc virtual server

da vo bng rule table. Mt real server s

c chn phc v bng cc thut ton

Load balancing , thng tin v kt ni ny

c lu vo bng hash table ghi nhn

kt ni. Tip theo , a ch ch v port

number ca packet c ghili cho ph hp vi server c chn

v packet c chuyn tip n

server. Khi m cc packet tip theo ca

kt ni c thit lp trc (kt ni

ny c tm thy trong bng hash table) v

cc packet ny sc ghi v chuyn n

cng server phc vn trc .

Ngoi thut ton LVS-NAT cn mt s

thut ton nh sau:

DNS (Domain Name Service) chnh tng server cho mi nhm ngi

dng c xc nh trc.

K thut chia tigim sngi dngcho mi my ch (Reducing the number

of users per server).

Linux Virtual Server - Tunnelling (TUN ).

Linux Virtual Server - Direct Routing.

Xy dng m hnh chia ti (Load

Balancing), chuyn i d phng (fail-

over), ng b d liu cc my ch ng

dng s dng k thut LVS (Linux

Virtual Server)

a, xut gii php

Tit kim chi ph, h thng khng cnqu u t cho nhn thit b qu chuyn

dng m c th tn dng nhng my

chang s dng ri chia ti ra.

m bo hiu sut ca h thng. Victng thm cc my ch (nodes) s lm

tng kh nng x l, cng nh chngchu li, cc cuc tn cng t chi dch

v (DoS, DDoS)

Khnng mrng cao, d dng thay thv b sung cc nodes trong mng m

khng lm nh hng n hot ng

ca h thng. Vi chc nng chia ti l

chnh, khi mt nodes gp s c d liu

s chuyn ti sang nodes khc.

b, M hnh trin khai:

- Gii thiu v m hnh:

Load Balancer 1 - Master (Ldirector 1):Sc cu hnh iu phi cc yu

cu t bn ngoi ti cc my ch thc

bn trong. My hot ng ch

Active.

Load Balancer 2 - Backup (Ldirector 2):My ny sc cu hnh tng tnh

my 1 nhng trng thi ch (Stand-

by). Khi my 1 gp s c th my 2 s

thay th vai tr ca my 1.


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Real Server: My ch ch ni dungdch v Website.

K thut s dng: Linux virtual ServerDirect Routing.

Thut ton s dng: Weighted RoundRobin: Thut ton ny iu phi cc

Real Server lun phin da vo kh

nng x l ca tng my. Thun li

vic thay th nng cp my ch, gim

chi ph khi mun nng cp.

Master v Backup s dng tn hiuHeartbeat trao i vi nhau, nu

Master c s c th Backup s thay th

vai tr ca Master. Khi Master x l

xong s c th Backup snhng li vai

tr cho Master.

Master dng Ldirector gim st ccReal Server. Nu mt trong cc Real

Server gp s c th Master ch chia

request cho cc Real Server cn li. Khi

Real Server b s c c khc phc

xong Master li tip tc chia request

cho Real Server .

M hnh Load Balancing LVSDirect Routing


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Kt lun:

Bi vit ny gii thiu tng quan

v Load Balancing v cc thut ton, chc

nng, u im v mt s k thut trong

Load Balancing. a ra m hnh trin khai

Load Balancing vi k thut LVS Direct

Routing lm mnh ha.

Ti liu tham kho:

[1] Sch in t: Load Balancing Servers Firewalls and Caches.

Tc gi: Chandra Kopparapu

[2] Bi vit: Load Balancer Topologies.

Tc gi: Jay Dobbs

[3] Sch in t: Linux Virtual Server Administration.

(Red Hat Enterprise Linux)

[4] Sch in t: Windows Server 2003 Clustering & Load balancing

Tc gi: Robert J. Shimonski

[5] Bi vit: Microsoft Network Load Balancing Technical Overview

[6] Sch in t: Network Load Balancing

Tc gi: Jonathan Held

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