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TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI VIỆN CÔNG NGHỆ THÔNG TIN Môn thiết bị truyền thông và mạng Đề tài:Load Balancing Giảng viện hướng dẫn: PGS.TS Ngô Hồng Sơn Nhóm thực hiện: Load Blancing 1

Load Balancing

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Load Balancing

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TRNG I HC BCH KHOA H NIVIN CNG NGH THNG TIN

Mn thit b truyn thng v mng ti:Load Balancing

Ging vin hng dn: PGS.TS Ng Hng SnNhm thc hin:Nguyn Hu Quyn CNCN-CNTT K56 2013699

Phm Thnh tCNTT-1.0120121503

Mc lc1. Gii thiu chung32.Khi nim33.Cc li ch ca Cn Bng Ti5a. Ti a ho Uptime5b. Gip Datacenter linh hot trong m rng5c. Tng tnh bo mt cho Datacenter64.Kin trc h thng cn bng ti75.Phn phi lu lng trong nhm86. Mt s thut toan load balancing11a. Thut ton ngu nhin:13b. Thut ton round robin (RR):14c. Thut ton Weighted Round Robin (Ratino):14d. Thut ton Dynamic Round Robin (DRR)15e. Thut ton Fastest.15f. Thut ton Lest Connection (LC)16g. Thut ton Observed16h. Thut ton Predictive177.Qu trnh hi t178.iu khin t xa199.Hiu nng cn bng ti1910.Thng lng v thi gian p ng yu cu2011.Mt s phng phap cn bng tai2112. DEMO cn bng ti DNS27

1. Gii thiu chungHin nay, khi nhu cu truy nhp mng bng n, cc server cung cp dch v ang tr nn qu ti. Vic la chn mt server n l c cu hnh cc mnh p ng nhu cu ny s ko theo chi ph u t rt ln. Gii php hiu qu c a ra l s dng mt nhm server 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. Mt k thut cn bng ti in hnh l RRDNS (Round Robin DNS). Vi gii php ny, nu mt server trong nhm b li, RRDNS s vn tip tc gi ti cho server cho n khi ngi qun tr mng pht hin ra li v tch server ny ra khi danh sch a ch DNS. iu ny s gy ra s t qung dch v. Sau nhng pht trin, t cc thut ton cn bng ti tnh nh Round Robin, Weighted Round Robin n cc thut ton cn bng ti ng nh Least Connection, Weighted Least Connection, Optimized Weighted Round Robin v Optimized Weighted Least Connection, k thut cn bng ti hin nay nh s kt hp cc thut ton trn ngy cng tr nn hon thin mc d nhc im vn c nh to im li n v vn nt c chai do s dng b iu phi tp trung (centralized dispatcher) vn cn. Trong phn bo co ny nhm chng ti xin gii thiu mt gii php m Microsoft s dng cho cc webserver, l k thut cn bng ti mng (NLB - Network Load Balancing).2.Khi nimServer ang l nn tng phn phi cc ng dng quan trng, thng xuyn v rng khp nh Web, Streaming media, VPN. Nh mt phn tch hp ca Windows Advanced Server v Datacenter Server, Network Load Balancing (NLB) cung cp mt gii php l tng, kinh t tng cng tnh kh m v kh dng cho cc ng dng trn c mi trng Internet v intranet.NLB m rng hiu nng ca cc server ng dng, chng hn nh Web server, nh phn phi cc yu cu ca client cho cc server trong nhm (cluster). Cc server (hay cn gi l host) u nhn gi IP n, nhng gi ch c x l bi mt server nht nh.

Cc host trong nhm s ng thi p ng cc yu cu khc nhau ca cc client, cho d mt client c th a ra nhiu yu cu. V d, mt trnh duyt Web cn rt nhiu hnh nh trn mt trang Web c lu tr ti nhiu host khc nhau trong mt nhm server. Vi k thut cn bng ti, qu trnh x l v thi gian p ng client s nhanh hn nhiu.

Mi host trong nhm c th nh ra mc ti m n s x l hoc ti c th phn phi mt cch ng u gia cc host. Nh s dng vic phn phi ny, mi server s la chn v x l mt phn ti ca host. Ti do cc client gi n c phn phi sao cho mi server nhn c s lng cc yu cu theo ng phn ti nh ca n.S cn bng ti ny c th iu chnh ng khi cc host tham gia vo hoc ri khi nhm. i vi cc ng dng nh Web Server, c rt nhiu client v thi gian m cc yu cu ca client tn ti tng i ngn, kh nng ca k thut ny nhm phn phi ti thng qua nh x thng k s gip cn bng mt cch hiu qu cc ti v cung cp kh nng p ng nhanh khi nhm server c thay i.Cc server trong nhm cn bng ti pht i mt bn tin c bit thng bo trng thi hot ng ca n (gi l heartbeat message) ti cc host khc trong nhm ng thi nghe bn tin ny t cc khc host khc. Nu mt server trong nhm gp trc trc, cc host khc s iu chnh v ti phn phi li ti duy tr lin tc cc dch v cho cc client.

Trong phn ln cc trng hp, phn mm client thng t ng kt ni li v ngi s dng ch cm thy tr mt vi giy khi nhn c p ng tr li.3.Cc li ch ca Cn Bng Tia. Ti a ho UptimeCn Bng Ti gip dn tri lu lng truy cp v truy xut gia hai hoc nhiu my ch. Trong trng hp li s c xy ra ti mt im my ch, Cn Bng Ti s pht hin vn v di chuyn lu lng truy cp n cc my ch online cn li, dch v cho ngi dng s khng b gin on.C ch Cn Bng Ti ca Long Vn Datacenter rt linh ng, c thit k t ng x l s c. Nu Cn Bng Ti tht bi, h thng qun l d phng s x l li trong khi vn duy tr hot ng cng IP o (VIP) gim thiu gin on hot ng.b. Gip Datacenter linh hot trong m rngKhi khch hng c nhu cu m rng h thng Datacenter, Cn Bng Ti s t ng iu phi gia cc my ch c v mi x l cc yu cu dch v m khng lm gin on qu trnh hot ng, x l. Khch hng s ch ng hn rt nhiu trong cng vic nh c ch Cn Bng Ti ca Long Vn Datacenter.

c. Tng tnh bo mt cho DatacenterThng thng khi ngi dng gi yu cu dch v ln h thng s c Cn Bng Ti tip nhn ri mi phn chia cho cc my ch bn trong x l. Qu trnh phn hi yu cu cng thng qua thnh phn Cn Bng Ti. Bng cch c th ngn chn ngi dng giao tip trc tip vi cc my ch, n i cc thng tin v cu trc mng ni b, ngn nga lun cc cuc tn cng trn mng hoc truy cp tri php.

4.Kin trc h thng cn bng ti ti a ho thng lng v kh dng, cng ngh cn bng ti s dng kin trc phn mm phn tn hon ton, trnh iu khin cn bng ti c ci t v chy song song trn tt c cc host trong nhm. Trnh iu khin ny sp xp tt c cc host trong nhm vo mt mng con pht hin ng thi lu lng mng n a ch IP chnh ca nhm (v cc a ch b sung ca cc host nhiu v tr khc nhau).Trn mi host, trnh iu khin hot ng nh mt b lc gia trnh iu khin card mng v chng giao thc TCP/IP, cho php mt phn lu lng mng n c nhn bi host . Nh , cc yu cu ca client s c phn vng v cn bng ti gia cc host trong nhm.H thng cn bng ti chy nh mt trnh iu khin mng (v mt logic) nm di cc giao thc lp ng dng nh HTTP hay FTP. Kin trc ny ti a ho dung lng nh vic s dng mng qung b phn phi lu lng mng n tt c cc host trong nhm v loi b s cn thit phi nh tuyn cc gi n tng host ring l.Do thi gian lc cc gi khng mong mun din ra nhanh hn thi gian nh tuyn cc gi (nh tuyn bao gm cc qu trnh nhn gi, kim tra, ng gi li v gi i), kin trc ny cung cp thng lng cao hn cc gii php da trn b iu phi. Khi tc ca mng v server tng ln, thng lng cng tng theo t l thun, do loi b c bt c s l thuc no vo vic nh tuyn da trn cc phn cng c bit.Trn thc t, b cn bng ti c th t thng lng 250Mbit/s trong cc mng Gigabit. Mt u im c bn khc ca kin trc phn tn hon ton l kh dng c tng cng vi (N-1) cch khc phc li trong mt nhm c N host. Cc gii php da trn b iu phi to ra mt im li k tha m ch c th c khc phc bng cch s dng mt b iu phi d phng v do ch cung cp mt cch khc phc li duy nht.Kin trc cn bng ti cng tn dng c nhng u im v kin trc cc thit b chuyn mch (switch) hoc cc b tp trung (hub) ca mng con trong vic ng thi phn phi lu lng mng n tt c cc host trong nhm. Tuy nhin, phng php ny lm tng "ti trng" trn cc chuyn mch do chim thm bng thng cng. y khng phi l vn trong phn ln cc ng dng nh dch v Web hay streaming media, do t l lu lng n ch chim mt phn rt nh trong tng lu lng mng.Tuy nhin, nu cc kt ni mng pha client n thit b chuyn mch c tc nhanh hn nhiu cc kt ni pha server, lu lng c th chim mt t l ln qu mc cho php ca bng thng cng pha server. Vn tng t s gia tng nu nhiu nhm kt ni trn cng mt thit b chuyn mch v cc bin php thit lp cc mng LAN o cho tng nhm khng c thc hin.Trong qu trnh nhn gi, vic trin khai ca NLB l s kt hp gia vic phn phi cc gi ti tng TCP/IP v nhn cc gi khc qua trnh iu khin card mng. Vic ny gip tng tc x l chung v gim tr do TCP/IP c th x l gi trong khi trnh iu khin NDIS (Network Driver Interface Specification) nhn gi tip theo. Trong qu trnh gi gi, NLB cng tng cng thng lng, gim tr v ph ph (overhead) nh tng s lng gi m TCP/IP c th gi trong mt kt ni. c c nhng ci thin v hiu nng ny, NLB thit lp v qun l mt tp hp cc b m gi v cc k hiu (descriptor) c s dng phi hp cc hot ng ca TCP/IP v trnh iu khin NDIS.5.Phn phi lu lng trong nhmNLB s dng hai lp broadcast hoc multicast phn phi ng thi lu lng mng n tt c cc host trong nhm. Trong ch hot ng mc nh l unicast, NLB s gn a ch trm lm vic (a ch MAC) cho card mng card mng c th hot ng (card ny gi l card nhm ? cluster adapter), v tt c cc host trong nhm c gn cng mt a ch MAC.Cc gi n do c nhn bi tt c cc host trong nhm v chuyn gi ti trnh iu khin cn bng ti lc. m bo tnh duy nht, a ch MAC c dn xut t a ch IP chnh ca nhm. V d, vi a ch IP chnh ca nhm l 1.2.3.4, a ch MAC unicast c t l 02-BF-1-2-3-4.Trnh iu khin cn bng ti s t ng sa a ch MAC ca card nhm bng cch thit lp mt thc th ng k v ti np trnh iu khin card nhm. H iu hnh khng cn phi khi ng li. Nu cc host trong cluster c gn vo mt thit b chuyn mch (swicth) ch khng phi mt b tp trung (hub), vic s dng chung mt a ch MAC s gy ra xung t do cc chuyn mch lp 2 ch c th hot ng khi cc a ch MAC ngun trn tt c cc cng ca thit b chuyn mch l duy nht. trnh iu ny, NLB sa a ch MAC ngun cho cc gi u ra l duy nht, a ch MAC ca nhm l 02-BF-1-2-3-4 c chuyn thnh 02-h-1-2-3-4, trong h l mc u tin ca host trong nhm. K thut ny ngn khng cho thit b chuyn mch tm ra a ch MAC thc s ca nhm v kt qu l cc gi n nhm c phn phi ti tt c cc cng ca thit b chuyn mch.Nu cc host trong nhm c kt ni trc tip vo mt hub, mt n a ch MAC ngun ca NLB trong ch unicast c th c v hiu ho trnh gy ra hin tng trn cho cc thit b chuyn mch ng ln (upstream). iu ny c th thc hin bng cch thit lp tham s ng k NLB l MaskSourceMAC=0. Vic s dng h thng chuyn mch ng ln ba mc cng c th hn ch trn cho cc thit b chuyn mch.

Ch unicast ca NLB c th lm v hiu ho qu trnh trao i thng tin gia cc host trong nhm c s dng card nhm. Khi cc gi ca mt host c gi i vi a ch MAC ch ging a ch MAC ngun, cc gi ny s b quay vng (loop-back) gia cc tng giao thc mng bn trong h thng pha gi v khng bao gi ra n ng truyn. Hn ch ny c th trnh c bng cch thm mt card mng th hai cho mi host. Trong cu hnh ny, NLB s dng mt card mng trn mng con nhn cc yu cu ca client v mt card mng khc thng c t tch bit trn mng con cc b trao i thng tin gia cc host trong nhm v vi cc server c s d liu cng nh cc file server gc. NLB ch s dng card nhm truyn cc bn tin "heartbeat" v lu lng iu khin t xa.Ch rng, trao i thng tin gia cc host trong nhm v cc host ngoi nhm khng bao gi b nh hng bi ch unicast ca NLB. Lu lng mng n mt a ch IP dnh ring cho host (trong card nhm) c nhn bi tt c cc host trong nhm do chng s dng chung mt a ch MAC. Do NLB khng bao gi cn bng ti lu lng i vi cc a ch IP dnh ring, NLB s lp tc phn phi lu lng ny n TCP/IP trn host nh. Cc host khc trong nhm coi lu lng ny l lu lng c cn bng ti v s loi b lu lng ny. Ch , nu lu lng mng n qu ln i vi cc a ch IP dnh ring c th nh hng n hiu nng khi h thng NLB hot ng trong ch unicast (tu theo s cn thit i vi TCP/IP trong vic loi b cc gi khng mong mun).NLB cung cp ch th hai phn phi lu lng mng n cc host trong nhm, ch multicast. Ch ny gn a ch multicast 2 lp cho card nhm thay v thay i a ch trm lm vic ca card. V d, a ch MAC multicast s c gn l 03-BF-1-2-3-4 tng ng vi a ch IP chnh l 1.2.3.4. Do mi host trong nhm c mt a ch trm lm vic duy nht, ch ny khng cn mt b card mng th hai trao i thng tin gia cc host trong nhm v n cng khng c bt c nh hng no n hiu nng ca ton h thng do vic s dng cc a ch IP dnh ring.Ch unicast ca NLB gy ra trn trn switch do s phn phi ng thi lu lng mng trn tt c cc cng. Tuy nhin, ch multicast ca NLB a ra c hi hn ch trn switch ngi qun tr h thng c th cu hnh mt mng LAN o trn switch cho cc cng tng ng vi cc host. C th lm c iu ny bng cch lp trnh cho switch hoc s dng giao thc IGMP hoc giao thc GARP, GMRP.NLB cn trin khai chc nng ARP m bo rng a ch IP chnh ca nhm v cc a ch IP o khc c th phn gii sang a ch MAC multicast ca nhm. (a ch IP dnh ring s tip tc phn gii sang a ch trm lm vic ca card nhm).6. Mt s thut toan load balancingNLB s dng thut ton lc phn tn hon ton nh x cc client n cc host trong nhm. Thut ton ny cho php cc host trong nhm a ra cc quyt nh cn bng ti mt cch c lp v nhanh chng cho tng gi n. N c ti u ho cung cp kh nng cn bng ti mt cch thng k i vi mt s lng ln cc yu cu nh do v s client to ra, in hnh l i vi cc Web server.Nu s client hoc cc kt ni client to ra cc ti qu chnh lch nhau trn server, thut ton cn bng ti s t hiu qu. Tuy nhin, tnh n gin v tc ca thut ton cho php cung cp hiu nng rt cao bao gm c thng lng cao v thi gian p ng ngn trong mt di rng cc ng dng client/server thng dng.

NLB x l cc yu cu ca client bng cch dn ng cho mt t l phn trm chn nhng yu cu mi cho tng host trong nhm. Thut ton khng p ng nhng thay i v ti trn mi host (chng hn nh ti CPU hay vn s dng b nh). Tuy nhin, qu trnh nh x s c thay i khi quan h thnh vin trong nhm thay i v t l phn trm ti phn b s c ti cn bng.Khi xem xt mt gi n, tt c cc host thc hin ng thi vic nh x thng k xc nh nhanh chng host no s x l gi . Qu trnh nh x s dng mt hm ngu nhin tnh mc u tin ca host da trn a ch IP v cng n ca client cng cc thng tin trng thi khc ti u ho vic cn bng ti. Host tng ng s chuyn gi t cc tng di ln tng TCP/IP cn cc host khc s loi b gi ny. Qu trnh nh x khng thay i tr phi quan h gia cc host trong nhm thay i, m bo rng a ch IP v cng n ca client cho trc s lun c nh x n cng mt host trong nhm.Tuy nhin, host c th trong nhm m a ch IP v cng n ca client nh x ti khng th c xc nh trc do hm ngu nhin c tnh n quan h thnh vin trong nhm hin ti v qu kh ti thiu ho kh nng nh x li.Nhn chung, cht lng cn bng ti c xc nh mt cch thng k bi s lng client to ra yu cu. Nh kt cu tng gim v s lng client theo thng k, s u n v cht lng ca thut ton cn bng ti s thay i nh. hot ng cn bng ti c chnh xc cao trn mi host trong nhm, mt phn ti nguyn h thng s c s dng o v phn ng trc nhng thay i ca ti. S tr gi v hiu nng ny phi c cn nhc so vi li ch ca vic ti a ho kh nng s dng cc ti nguyn trong nhm (v c bn l CPU v b nh).Trong bt c trng hp no, vic s dng hp l cc ngun ti nguyn server phi c duy tr c th phc v cho cc ti client khc trong trng hp xy ra li.Khi mt host mi tham gia vo nhm, n s kch hot qu trnh hi t v mt quan h thnh vin mi trong nhm s c tnh ton. Khi qu trnh hi t hon thnh, mt phn ti thiu client s c nh x ti host mi. NLB d cc kt ni TCP trn mi host v sau khi kt ni TCP hin ti ca chng hon thnh, kt ni tip theo t cc client b nh hng s c x l bi host mi.Do , cc host nn c b sung vo nhm ti nhng thi im ti tng qu mnh nhm ti thiu ho hin tng ngt qung cc phin. trnh vn ny, trng thi phin phi c qun l bi ng dng server sao cho n c th c ti cu trc hay c tr li t bt k mt host no trong nhm. V d, trng thi phin c th c y n server c s d liu v lu trong cc cookies ca client.a. Thut ton ngu nhin:Trong thut ton random, kt ni s c phn mt cch ngu nhin vo server ng sau bng cch s dng mt hm chn s ngu nhin.Mc d thut ton ny c ci t sn trong cc b cn bng ti, tuy nhin n t c p dng so vi cc thut ton khc.b. Thut ton round robin (RR):Round robin l thut ton c s dng nhiu nht trong cc h thng load balance va v nh, nhu cu m rng h thng thp. Mt kt ni vi s c gi n server k tip pha backend v c tip tc quay vng nh vy.Round robin hot ng tt khi cc server backend c cu hnh (ti nguyn) tng t nhau v s xy ra hin tng mt cn bng ti khi cc server backend c cu hnh khc nhau (xy ra hin tng mt s server x l nhiu hn server khc). Tuy nhin v l thut ton n gin nn n t ra hot ng rt nhanh v hiu qu (khng p dng thut ton phc tp, khng mt nhiu thi gian tnh ton, ). Trong qu trnh p dng, nu cc server ch khng b s c th vic p dng thut ton round robin cho hiu qu kh quan.im yu ca round robin l 2 yu cu lin tc t pha ngi dng s c th c gi vo 2 server khc nhau. iu ny lm tn thi gian to thm kt ni vi server th 2 trong khi server th nht cng c th tr li c thng tin m ngi dng ang cn. gii quyt iu ny, round robin thng c ci t cng vi cc phng php duy tr session nh s dng cookie.c. Thut ton Weighted Round Robin (Ratino):Nguyn l hot ng ca WRR cng tng t nh RR, yu cu t pha ngi dng s c b cn bng ti chuyn n cc backend theo th t xoay vng. S khc bit duy nht y l thut ton WRR cn c kh nng x l theo cu hnh ca tng server ch. Trong cng mt chu k, mt server c kh nng x l gp i server khc s nhn c s request gp i t b cn bng ti.V d: C 4 server A,B,C,D trong hai server A, B c cu hnh tng t nhau. Cu hnh ca C v D cng tng t nhau v gp i cu hnh ca A. Khi trng s c nh cho A v B l 1, nh cho C v D l 2. Vy theo lut ca WRR th th t server nhn c request t b cn bng ti s l ABCCDD.Thut ton WRR hot ng tt hn RR khi trong cm backend c cc server cu hnh khc nhau. Tuy nhin s dng thut ton ny c th dn n vic mt cn bng ti ng nu nh ti ca cc request lin tc thay i trong mt khong thi gian rng (v d cc yu cu cn xem video hoc ti cc file c dung lng ln xen k vi cc yu cu c thng tin,). Trong mt khong thi gian ngn, hon ton c kh nng phn ln cc yu cu c ti cao s c chuyn hng n mt server.d. Thut ton Dynamic Round Robin (DRR)Thut ton DRR hot ng gn ging vi thut ton DRR, im khc bit l trng s y da trn s kim tra server mt cch lin tc, do trng s lin tc thay i.y l thut ton ng (cc thut ton trn l thut ton tnh), vic chn server s da trn rt nhiu kha cnh trong vic phn tch hiu nng ca server trn thi gia thc (v d: s kt ni hin ang c trn cc server hoc server tr li nhanh nht, ).Thut ton ny thng khng c ci t trong cc b cn bng ti n gin, n thng c s dng trong cc sn phm cn bng ti ca F5 Network.e. Thut ton Fastest.Thut ton fastest chn server da trn thi gian p ng ca mi server (response time), thut ton ny s chn server no c thi gian p ng nhanh nht. Thi gian p ng c xc nh bi khong thi gian gia thi im gi mt gi tin n server v thi im nhn c gi tin tr li. Vic gi v nhn ny s c b cn bng ti m nhim, da trn thi gian p ng, b cn bng ti s bit chuyn yu cu tip theo n server no.Thut ton fastest thng c dng khi cc server c ci t dc theo cc mng logic khc nhau, ngha l server c t nhiu ni khc nhau. Nh vy ngi dng gn server no th thi gian p ng ca server s nhanh nht, v server s c chn phc v.Thut ton ny cng ging nh chuyn hng yu cu da trn a ch IP. V d nh khi truy cp vo trang youtobe.com, nu IP ca ngi dng n t Vit Nam, yu cu s c chuyn vo server Vit Nam x l. iu ny s tit kim kh ln cho lng bng thng quc t v ci thin tc ng truyn.f. Thut ton Lest Connection (LC)Thut ton LC, yu cu t pha ngi dng s c chuyn vo server c t kt ni nht trong h thng ti thi im . Thut ton ny c coi nh thut ton ng, v n phi m s kt ni ang hot ng ca server.Vi mt h thng c cc server gn ging nhau v cu hnh, LC c kh nng hot ng tt ngay c khi ti ca cc kt ni bin thin trong mt khong ln. Do nu s dng RC s khc phc c nhc im ca RR.Nhn bn ngoi c v nh LC hot ng tt khi cc server c cu hnh bin thin khc nhau, tuy nhin trn thc t u l khng ng. Nguyn nhn l do trng thi TIMVE_WAIT ca TCP. TIME_WAIT thng c t l 2 pht, trong 2 pht c mt server bn rn c th nhn hng chc ngn kt ni lin tc. Gi s server A c kh nng x l gp i server B, server A ang x l hng ngn nhng yu cu v gi nhng yu cu ny trong trng thi TIME_WAIT ca TCP. Trong khi server B cng phi x l nh server A nhng v cu hnh server B thp hn nn s chm hn rt nhiu. Nh vy thut ton LC hot ng khng tt khi cc server c cu hnh khc nhau.g. Thut ton ObservedObserved l s kt hp ca thut ton LC v Fastest Response, n ch tn ti trong cc gii php ca F5 Network. y ngi pht trin h thng s phi cn bng gi hai yu t l s kt ni n tng server v thi gian p ng gia chng. Ngha l cng ging nh nh trng s cho cc server, hai yu t ny s c nhng trng s nht nh da trn nhn nh ca ngi pht trin h thng hoc nh qun tr. Mt php ton s hc da trn s kt ni ca mt server thi gian p ng v cc trng s s a ra cho mi server mt gi tr. Da trn gi tr , b cn bng ti s chn c server ph hp.Nu nh c thit k tt, Observed s khc phc c c nhc im ca Lest Connection v Fastest Response. Thut ton Lest Connection s khng ch trng vo khng gian, c ngha l mt ngi truy cp t H Ni c th kt ni vi server t ti H Chnh Minh v ngc li v s kt ni ang t nht. Nh vy l khng cn thit, v nu chuyn kt ni ngi dng ny vo server ti H Ni th thi gian phc v s gim xung ng thi tit kim c rt nhiu bng thng. Trong khi Fastest Response s a ngi dng vo server c thi gian p ng nhanh nht bt k s kt ni l nhiu hay t, nu nh my ch sp qu ti c th dn n b treo. S cn bng gia s kt ni v thi gian p ng s gip cho b cn bng ti la chn c server ph hp.Observed c a ra bi F5 Network v hu nh khng tn ti trong cc phn mm m ngun m hay cc phn mm nh.h. Thut ton PredictiveL s pht trin tip theo ca Observed, nhng trong thut ton predictive h thng s phn tch trng thi ca cc server theo thi gian thc, xc nh xem thi im no th hiu nng ca server ang tng ln, thi im no ang gim xung. Nh vy gi s 2 server theo nh gi ca thut ton predictive l tng ng nhau, server no c hiu nng bin i theo chiu hng tt hn s c chn.

7.Qu trnh hi tCc host trong nhm trao i nh k cc bn tin "heartbeat" multicast hoc broadcast vi nhau. iu ny cho php cc host c th gim st trng thi ca nhm. Khi trng thi ca nhm thay i (chng hn nh khi c host gp trc trc, ri khi hoc tham gia vo nhm), NLB kch hot mt chu trnh gi l hi t trong cc host trao i bn tin "heartbeat" nh ra mt trng thi mi, bn vng cho nhm. Khi tt c cc t c s "nht tr" trng thi mi ca chng s c thit lp v nhng thay i ny s c lu vo nht k s kin.Trong qu trnh hi t, cc host tip tc x l lu lng mng n nh mi khi ngoi tr lu lng n host b li khng nhn c dch v. Qu trnh hi t kt thc khi tt c cc host trong nhm c c mt quan h thnh vin n nh trong vng mt vi chu k heartbeat.Khi hon thnh qu trnh hi t, lu lng n host b li s c ti phn phi cho cc host cn li. Nu mt host c thm vo nhm, qu trnh hi t cho php host ny nhn c phn ti ca n trong lu lng c cn bng.Vic m rng nhm khng nh hng n cc hot ng ca nhm v theo mt cch hon ton trong sut i vi tt c cc Internet client cng nh trc cc chng trnh phn mm server. Tuy nhin, n c th nh hng n cc phin client v cc client c th phi ti nh x ti cc host khc trong nhm.

Trong ch unicast, mi host s pht qung b (broadcast) bn tin "heartbeat" theo chu k. Cn trong ch multicast, n s pht cc bn tin ny ch multicast. Mi bn tin "heartbeat" chim mt khung Ethernet v c gn thm a ch IP chnh ca nhm nhm cho php nhiu nhm c th cng tn ti trn cng mt mng con. Bn tin "heartbeat" ca NLB ca Microsoft c gn mt gi tr 0x886F. Chu k gi cc bn tin ny mc nh l 01 giy. Gi tr ny c th thay i.Trong qu trnh hi t, chu k ny c gim xung ch cn mt na y nhanh vic hon tt qu trnh ny. Thm ch, i vi cc cluster ln, bng thng cn thit truyn cc bn tin "heartbeat" rt thp (24kBytes/s cho mt cluster 16 ng). c th khi to qu trnh hi t, theo mc nh cn 05 bn tin heartbeat khng c nhn. Gi tr ny c th thay i.8.iu khin t xaC ch iu khin t xa ca NLB s dng giao thc UDP v c gn cng dch v #2504. Cc gi d liu iu khin t xa c gi ti a ch IP chnh ca nhm. Do trnh iu khin trn mi host trong nhm x l cc gi ny, chng cn c nh tuyn ti mng con ca nhm (thay v ti mt mng con gc m nhm gn vo). Khi cc lnh iu khin t xa c a ra trong nhm, chng s c pht qung b trn mng con cc b.iu ny m bo tt c cc host trong nhm u c th nhn c chng ngay c khi nhm chy trong ch unicast.9.Hiu nng cn bng tiVai tr ca NLB tc ng n hiu nng ca h thng c th c nh gi da trn bn tiu ch chnh sau:- CPU overhead trn cc host ca nhm - Phn trm CPU cn thit phn tch v lc cc gi ca mng (cng thp cng tt).Tt c cc gii php cn bng ti u cn s dng mt phn ti nguyn ca h thng xem xt gi n v a ra quyt nh cn bng ti v do t nhiu nh hng n hiu nng ca mng.Gii php cn bng ti da trn b iu phi cn kim tra, hiu chnh v truyn li gi ti cc host trong nhm (thng phi sa i li a ch IP ti nh tuyn gi t a ch IP o ti a ch IP ca tng host c th). i vi NLB, n phn phi ng thi cc gi n ti tt c cc host trong nhm v p dng mt thut ton lc loi b cc gi khng mong mun...Qu trnh lc gy nh hng t hn so vi qu trnh ti nh tuyn v kt qu l thi gian p ng nhanh hn vi thng lng ton h thng cao hn.10.Thng lng v thi gian p ng yu cuNLB nng cao hiu nng h thng bng cch tng thng lng v ti thiu ho thi gian p ng ti cc yu cu ca client. Khi nng lc ca cc host trong nhm c khai thc ti a, n s khng th cung cp thm thng lng v thi gian p ng tng t bin tu theo tr hng i cc yu cu ca client. B sung thm host s cho php tng thng lng v gim thi gian p ng.Nu nhu cu ca khch hng tip tc tng, cc host s c thm vo cho n khi mng con bo ho. V nu ti tip tc tng, cn s dng nhiu nhm NLB v vic phn phi lu lng gia cc host c thc hin bng k thut Round Robin DNS.

- Bng thng s dng ca Switch (Switch occupancy): T l bng thng ca switch c s dng bi qu trnh lm trn cc yu cu ca client.Kin trc lc gi ca NLB da trn mng con broadcast phn phi cc yu cu ca client ti tt c cc host cng lc. Trong cc nhm nh, c th s dng hub kt ni cc host. Vi cc nhm ln hn, switch s l s la chn. V nh mc nh, NLB s to ra hin tng "trn" switch c th phn phi cc yu cu ca client ti tt c cc host cng lc.Cn chc chn rng hin tng "trn" switch khng c vt qu nng lc ca switch, c bit khi switch c chia s gia nhm v cc my tnh ngoi nhm. Bnh thng, bng thng s dng cho lu lng yu cu ca client ch chim mt t l nh trong tng lng bng thng cn thit cho qu trnh truyn thng gia server v client.Tuy nhin qu trnh "trn" switch s tr thnh vn trong nhng ng dng c t l phn trm ng k lu lng mng c dn ti nhm (chng hn nh qu trnh upload file trong cc ng dng FTP) hay khi nhiu nhm s dng chung mt switch. Trong nhng trng hp ny, chy NLB trong ch multicast v thit lp mng LAN o hn ch trn switch l bin php khc phc rt hiu qu khim khuyt ny. Ngoi ra, tnh kh m ca NLB quyt nh kh nng ci thin hiu nng ca h thng khi cc host c thm vo nhm.11.Mt s phng phap cn bng taiRound Robin DNS:1. Cn bng ti cho server ton cu ( GSLB) C 2 nhn t chnh th hin s cn thit ca GSLB , l kh nng c sn cao v thi gian p ng. m bo tnh c sn ca cm server , chng ta s dng 1 b cn bng ti thc hin kim tra health checks i vi server. m bo b cn bng ti khng b qu ti chng ta c th ci t nhiu b cn bng ti hot ng. Chng ta gii thit rng c s c l b trung tm d liu cha cc server v cc b cn bng ti khng th hot ng v mt in, ng t hoc l lt? Tt nhin l ngi dng s khng th truy cp vo website. trnh trng hp ny xy ra, chng ta c th ci t website nhiu trung tm d liu khc nhau v s dng GSLB ng b gia cc trung tm ny. Phng n ny m bo rng , nu nh c mt trung tm no b hng, th vn cn cc trung tm khc hot ng.2. Domain Name System ( DNS )GSLB c th t c nhiu cch khc nhau, nhng cch c dng nhiu nht l DNS . Khi ngi dng truy cp vo website v d l www.facebook.com chng hn, th facebook.com chnh l tn min (domain) , c nhiu loi tn min khc nhau, ch nh bng ui ca chng. V d tn min .com ( cc trang web thng mi ) , tn min .org( gio dc). Trong mi tn min li c nhng tn min con gi l cc vng ca tn min chnh. V d : pics.facebook.com hay l video.facebook.com . Mt tn min c th c lu tr nhiu DNS khc nhau , nhng s c mt DNS c thm quyn cao nht ( authoritative DNS) , DNS ny c trch nhim cp nht tt c cc thay i cho cc DNS c thm quyn thp hn.

3. Cn bng ti bng DNS C 3 phng php cn bng ti vi DNS : round robin , random v location-based. Trong " round robin" l phng php c xem l d thc hin v thng dng nht. * ROUND ROBIN LOAD BALANCING ( Lun chuyn vng DNS )Hu ht chng ta u bit, c s d liu DNS bn ha tn host thnh cc a ch IP.

Khi bn nhp mt URL vo trong trnh duyt (v d nhwww.loadbalancedsite.com) th trnh duyt s gi mt yu cu n DNS yu cu n tr v a ch IP ca site. y c gi l vic tra cu DNS. Sau khi trnh duyt Web c c a ch IP cho site th n s lin h vi site bng a ch IP, v hin th trang m bn va yu cu. My ch DNS thng c mt a ch IP c bn ha vi mt tn site no . Trong v d ring ca chng ti th site lwww.loadbalancedsite.combn ha thnh a ch IP l203.24.23.3.

cn bng ti bng DNS, my ch DNS phi duy trnh mt s a ch IP khc nhau cho cng mt tn site. Nhiu a ch IP th hin nhiu my trong mt cluster, tt c trong s chng u bn ha n mt tn site logic. Trong v d ca chng ta,www.loadbalancedsite.comc th c cu hnh trn ba my ch trong mt cluster vi cc a ch IP di y:203.34.23.3203.34.23.4203.34.23.5Trong trng hp ny, my ch DNS c bn ha nh sau:www.loadbalancedsite.com 203.34.23.3www.loadbalancedsite.com 203.34.23.4www.loadbalancedsite.com 203.34.23.5

Khi yu cu u tin n c my ch DNS, n s tr v a ch IP203.34.23.3, my u tin. Khi c yu cu th hau, n s tr v a ch IP th hai:203.34.23.4. Tip tc nh vy, vi yu cu th t, a ch IP u tin li c lp li.

Bng cch s dng lun chuyn vng DNS nh trn, tt c cc yu cu i vi mt site no u c phn phi u n tt c cc my trong cluster. Chnh v vy, vi phng php cn bng ti ny, tt c cc nt trong cluster u c s dng.u im ca phng php lun chuyn vng DNS

Cc u im chnh ca phng php ny nm ch r v d dng:

Khng t v d dng thit lp: Cc qun tr vin h thng ch cn to mt s thay i trong my ch DNS h tr c vic lun chuyn vng, v nhiu my ch DNS c s h tr ny. N khng yu cu n s thay i m ca ng dng Web; trong thc t, cc ng dng Web khng h bit v c ch cn bng ti m n b thc hin.

n gin: Phng php ny khng yu cu n cc chuyn gia v mng trong vic thit lp hoc gi ri h thng trong trng hp c vn no xay ra.

Nhc im ca phng php ny

C hai nhc im chnh ca phng php da trn phn mm ny l n khng cung cp s h tr mi quan h thi gian thc gia cc my ch vi nhau v khng h tr kh nng c sn cao.

-Khng h tr mi quan h thi gian thc gia cc my ch. Mi quan h thi gian thc gia cc my ch l kh nng ca h thng trong vic qun l cc yu cu ca ngi dng, my ch ny hoc bt k my ch no, ph thuc vo thng tin session c duy tr trn my ch hoc ti mc c s bn, mc c s d liu.

Khng c c kh nng h tr mi quan h gia cc my ch, phng php lun chuyn vng DNS da vo mt trong ba phng php c a ra duy tr s kim sot session hoc s nhn dng ngi dng i vi cc yu cu ang n trn HTTP. Cc cookie Cc trng n Vit li URLKhi mt ngi dng thc hin mt yu cu u tin, my ch Web s tr mt th bng vn bn duy nht phn bit ngi dng . Cc yu cu tip theo c th ny s dng cookie, vit li URL hoc cc trng n, cho php my ch xut hin duy tr mt session gia my khch v my ch. Khi ngi dng thit lp mt session vi mt my ch, th tt c cc yu cu n sau thng u i n cng mt my ch.

Vn y l trnh duyt lu a ch IP ca my ch . Khi Cache ht hn, trnh duyt s thc hin mt yu cu khc i vi my ch DNS c c a ch IP c lin kt vi tn min. Nu my ch DNS tr v mt a ch IP khc, mt my ch khc trong cluster, th cc thng tin v session s b mt.

-Khng h tr cho kh nng c sn cao. Xem xt mt cluster c n nt. Nu mt nt no gp vn th c yu cu th n n my ch DNS u hng bn n mt nt hng ny. Mt router thng minh c th gii quyt c vn ny bng cch kim tra cc nt cc khong thi gian no , pht hin ra cc nt b hng v g b chng ra khi danh sch, chnh v vy s khng c yu cu no c gi n chng na. Tuy vy, vn y vn tn ti nu nt vn c nhng ng dng Web ang chy trn nt b hng.

Thay i cluster s mt nhiu thi gian truyn b n ton b phn cn li ca Internet. Mt l do y l trong nhiu t chc ln cc ISP, cc cng ty, hay i l lu cc yu cu DNS ca h gim lu lng mng v thi gian request. Khi ngi dng bn trong cc t chc nh vy thc hin mt request th h thng s c kim tra danh sch cc tn DNS ca Cache c bn ha a ch IP. Nu h thng pht hin thy mt entry no th n s tr a ch IP v cho ngi dng. Nu n khng pht hin thy entry no trong Cache ni b th ISP s gi request DNS ny n my ch DNS v lu s p tr.

Khi mt entry c lu ht hn, ISP s nng cp c s d liu ni b ca n bng cch lin h vi cc my ch DNS khc. Khi danh sch cc my ch ca bn thay i, n c th cn n mt khong thi gian ngn cho cc entry c lu trn mng ca cc t chc khc ht hn v tm kim danh sch cc my ch c cp nht. Trong sut chu trnh ny, my khch vn c th thc hin hnh ng hit nt my ch b hng, nu ISP ca my khch vn c mt entry tr n n. Trong trng hp nh vy, mt s ngi dng ca ISP khng th truy cp vo site ca bn t nhng ln truy cp ban u, thm tr nu cluster ca bn c cc my ch d tha vn ang hot ng.

Mt vn cn ln hn xut hin khi g b (removing) mt nt so vi vic b sung. Khi bn bt i mt nt, ngi dng c th ang thc hin hit mt my ch khng tn ti. Cn khi bn thm mt nt th my ch vn cha c s dng cho ti khi a ch IP ca n n c tt c cc my ch DNS.

Mc d phng php ny c th cn bng c mt s lng ngi dng trn mi my ch, nhng n khng hon ton cn bng ti my ch. Mt s ngi dng c th yu cu mc ti cao hn trong sut mt session ca h so vi nhng ngi dng khc trn my ch khc, v phng php ny khng th bo m chng li c s bt cng bng .12. DEMO cn bng ti DNSBi lab gm c 5 server, mi server l mt trang html c ni dung khc nhau phn bit vi nhng trang khc. ci t n gin th router tnh c s dng tt c cc thit b.Cc client c cu hnh c th kt ni t mt im n cc server cc b

Root-ns : tn ca server gcNs1 c y quyn cho example.usNs2 c y quyn cho test.euServer 3 c y quyn cho web.com Cc k thut cn bng ti khc nhau:+ Round robin+ Location based+ RandomC nhiu nt A c ghi li bi www.web.com ca mi server trong mt khu vcTt c c ghi li khi client thc hin mt truy vn1. Round robin load balancing DNS Thut ton lun chuyn vng, cc my ch s c xem ngang hng v sp xp theo mt vng quay. Cc truy vn dch v s ln lt c gi ti cc my ch theo th t sp xp.

Thc hin truy vn cc thi im khc thy ni dung khc nhau

Count_server_replies.sh ghi li 100 yu cu ti www.web.com v m s ln tr li ca mi server

2. Location based load balancing DNSKhi thc hin cu truy vn mt vng th ta c th nhn c cc d kiu khc nhau t nhng server khc nhau, hay cn gi l kiu cn bng ti theo cc bChy link trn client1 lun thy c cc trang t nhng server khc nhau

3. Random load balancing DNS: Trong thut ton random, kt ni s c phn mt cch ngu nhin vo server ng sau bng cch s dng mt hm chn s ngu nhin.Order random: Th t khc nhau c s dng khi ghi li li cc client

Do , cc my khch khu vc US s truy cp v ghi li mt cch ngu nhin nhng vn theo kiu round robin

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