Load Balancing Algorithm for Web Server Based on Weighted Minimal Connections

Transcription

1 Journal of Web ystes and Applcatons (2017) Vol. 1, Nuuber 1 Clausus centfc Press, Canada Load Balancng Algorth for Web erver Based on Weghted Mnal Connectons Pan Zhu1, a, Jangxng Zhang 2,b College of Inforaton Engneerng, Zhejang Unversty of Technology, Hangzhou, Chna a @qq.co, b zjx@zjut.edu.cn Keywords: Web server cluster, Dynac feedback, Load balancng, Weghted nal connecton nuber algorth, OPNET. Abstract. We have analyzed the clusterng technology of Web server and studd the load balancng algorth, due the lack of the exstng load balancng algorth can not accurately reflectng the sze of the server load and anually settng the weght and other aspects, n ths paper,we propose an proved weghted nu jon Iproved Load Balancng Algorth for Web server cluster. On the one hand,the algorth takes nto account server utlzaton, eory utlzaton and network bandwdth utlaton and other factors, cobned wth web server s own characterstcs,accoudng to the real-te load of the server to dynacally change the sze of the weght, and on the other hand, assgns the new connecton request accordng to the weghted nu connecton nuber algorth. Through the use of sulaton software OPNET, the algorth not only reduces server latency, reduces HTTP response te,and can effectvely prove the load balancng effcency. 1. Introducton In recent years, as the rapd developent n Internet, the deand of the network servce s also growng, whch leads to the page loadng s too slow and the webste s not respondng n the case of hgh concurrent data request.thus It has becoe an urgent proble for webste anagers.when a sngle server load s too large, the usual ethod s upgrate the host. However, the ablty of a sngle host s lted and hgh perforance host s expensve. In addton, the server cluster s low-cost and has good scalablty, whch has becoe an effectve ethod to solve ths proble. A cluster conssted a group of coputers that are ndependent of each other, nterconnected by hgh-speed networks and anaged n a sngle syste ode[1]. Load-balancng syste s the core part of server cluster[2], and the load-balancng algorth s the key to delver user s requests [3]. The exstng load-balancng algorths can be dvded nto two categores: statc and dynac. The statc load-balancng algorth assgns tasks wth the fxed probablty, whch do not consder the state nforaton of the server; Dynac balancng-algorth assgns tasks based on real-te load status nforaton of the server. Dynac balancng-algorth conssted nu connecton ethod, weghted least connecton ethod, nu connecton ethod based on locaton. In practcal applcaton, there are any factors affectng clent access frequency, node network-load, whch are dffcult to predct; If the syste s long te runnng, the load can t be tely corrected, hence the effects of the load-balancng s not good [4]. Many Researchers have 1

2 studed the load-balancng algorths and proved the. Lu proposed a load-balancng algorth based on dynac feedback [5], whch consders the node perforance, real-te load of the server and assgns the task accordng to the dynac feedback. Ths algorth does not ake use of the node perforance and real-te load when assgnng the task thus ts perforance s not good. Geng proposed a load-balancng algorth based on adaptve weght. Ths algorth reflects real-te by adaptve weght [6] ;Wang.el proposed proved actve load-balancng algorth by adjust paraeter n receve staton serverb by WEB clustered syste whch could waste too uch copute cost.besdes l [7]. In suary, by copare the advantage and dsavantage both statc load-balancng and actve load-balancng algorth,ths paper proposed an poved algorth wth weghted nu connect nuber, by adjust balance the sever qualty and actve weght,then cobne sever node as actve connecton nuber to assgn tasks. 2. Tradtonal load balancng algorth The an task of the load balancng odule s to receve network requests, and calculate the server s load. Load balancng polcy s adjusted by load balancng algorth durng server operaton, And then dstrbute the request to the approprate server, fnsh the load balancng process fnally. In the exstng load balancng algorth, There are soe load balancng algorths based on real-te load condtons, The exstng weghted nu connecton (WLC) algorth can effectvely balance the load of the server cluster and dstrbute user requests. 2.1 Weghted Mnu Connecton Nuber Algorth (WLC) Weghted least connecton algorth s based on the nu connecton (LC) algorth. When the load balancer receves a new task request, t responds to the task request by selectng the one has the sallest rato of erver connecton nuber and weght n the current server group. Assung that the server set s = (1, 2... n), the ntal weght of the -th server s W () (1 n), the current connecton nuber C (). When the load balancer receves a new connecton request, t selects the server ( )for servce accordng to the followng rules: C( )/ W( ) nc ( )/ W( ) [1 2,, n ], W( ) 0 (1) aong the, (1) the calculaton of dvson s ore coplex than ultplcaton, so the dvson calculaton spends ore CPU cycle. Then the Judgent rule C( )/ W( ) C( )/ W( ) can be effectvely expressed by C( ) W( ) C( ) W( ),In the condtons above, the server's weght can not be zero (when the value s zero, the server s not scheduled). The current WLC algorth take the dfferences n perforance of each server and the effect of connecton nuber nto consderaton. t greatly proves the effcency of the syste. But reflectng the server's load status only by the current nuber of connectons s not reasonable enough. It s also possble to dynacally adjust the server weghts accordng to the current response of the server for the unbalanced load between the servers. 2.2 Weghted Round-Robn algorth (WRR) Weghted Round-Robn algorth s an proveent of the classcal Round-Robn algorth. Ths algorth accordng to the perforance of each server to assgn dfferent weghts for each server perforance s nconsstent. Its weght s relatvely hgh for hgh perforance server and t can accept the request s ore; It s weght s relatvely low for low perforance and t can receve fewer requests. 2

3 In the process of schedulng algorth, the request s carred out by the cyclc schedulng of the queue. It s a good soluton to a sngle request pattern proble. Weghted Round-Robn algorth have soe characterstcs: It added the concept of weght on the bass of classcal pollng algorth. However, the algorth does not consder the effect of the nuber of connectons and the state of the server and t cannot respond to server status n real te. It belongs to the statc algorth, and t has the ltaton. 3. Desgn and Ipleentaton of Iproved Algorth In order to copensate for the shortcongs of the weghted nu connecton nuber algorth, ths paper proposes a load balancng proveent algorth for weghted nu connecton nuber for Web server. In the load balancng process, we consder the processng capablty of the background server and the current load of the background server. Accordng to the sze of each server's current load scale value of the reasonable allocaton of the request whch s real-te collecton of server data nforaton to change the tradtonal load calculaton ethod, and these etrcs and WLC algorth to acheve proved algorths to prove the user request schedulng effcency purpose. 3.1 Node perforance evaluaton and real-te quantzaton of load The load ndex s the standard for the load evaluaton quantfcaton, and the choce of dfferent load ndcators wll lead to dfferent load levels of the load at the sae te. If all the resources of the host as a load ndcator s unrealstc, one s a wde varety, the second s the collecton and calculaton are very coplex, so a good load ndcators should have the followng condtons: (1) easy to obtan the ndex data to facltate Multple easureents; (2) the ndex data can objectvely reflect the load stuaton. 3.2 Evaluaton of node perforance Due to dfferent types of servces, the pact of varous ndcators on the load s also dfferent. Acc ordng to the stuaton to adjust the poston of each ndex n the load, only need to change the corre spondng weghts can be. The results show that the effcency of cluster s dfferent when usng dff erent factors. The character of Web server based on HTTP request, for perforance of the node n t he cluster syste anly fro the nuber of CPU n, CPU frequency, eory capacty, dsk rate, n etwork throughput and other ndcators to consder, usng equaton (1) to calculate. C ) k C( C ) k C( D ) k C( N ) 0 1,,, n 1, k 1 (2) ( Calculaton of the syste load In the paper, the server load s defned as L, C s the CPU usage, the eory occupancy rate s M, the usage of the connecton s P, the network bandwdth occupancy rate s B, and D represent the dsk usage and C, M, P, B, D [0 1, ].For a foral forula, we usually gve a forula for weghtng the su of the data, as shown n Eq. 3: L 1C 2M 3P 4B 5D (3) In (Eq. 3) each utlzaton factor represents the portance of each resource n the overall load. After the noralzaton of the coeffcents, the fnally results s L [0 1, ].When the usage of soe resources s hgh, the syste wll crash. The cuulatve su of each coeffcent s 1, n Eq.3, so t 3

4 can only represent the portance of a specfy resource, but can not equally reflect other resources. In the fuzzy set theory, there are three knds of weghted ntegrated ethod: weghted average ethod, product ean ethod, xed ethod. When utlzaton rate of the resource exceeds a certan value,and the ablty of the syste recevng new requests sgnfcantly declne, We should choose the product ean ethod [8]. In ths paper, we use the product ean ethod to descrbe the server load, as shown n Equaton 4: L 1 (1 C)(1 M )(1 pp)(1 B)(1 D) 0, 且 0 (1 X ) 1 (4) c b In (Eq. 4), f an applcaton has a greater pact on one or ore of these ndcators, the correspondng coeffcent can be ncreased, and the su of the coeffcents s no longer equal to 1, thus t s ore objectve descrpton of the load generated by the server. 4. The perodc adjustent of weghts 4.1 Load condton deternaton The load-balancer perodcally receves the current load of the server and changes the value of weg ht accordng to the coparson wth the value of the load and the threshold. Where the threshold h ere changes wth the value of the ncong load. As the threshold s represented by the rto of the p erforance of the current server versus all servers: C L (5) C When L ( ),we state the current load of the server node s a low load, ndcatng that the load s relatvely lght at ths te, then ts weght should be ncreased; whenl ( ), we state the current load of the server node s a hgh load, ndcatng that the load s relatvely heavy at ths te, then ts weght should be reduced.and n ths paper,we have ntroduced a odfed varable,t wll calculate n the followng foula (6): d 1 - (1/n) C( n 1 )/W( C( ) )/W( ) W ) ndcates the ntal weght of the server, C ) ndcates the current nuber of ( connectons for the server,and W ) can not be zero. The new weght can be expressed as: ( W ( ), L( ) W( ) W ( ), L( ) (7) The new weght of the node W ( ) s perodcally acqured, elect the server wth the sallest rato between the current connecton and the updated weght to accept the new connecton request,naely the server accept the new request,at the sae te,t would satsfy: C ) W( )' n C( ) W( )' (8) ( ( (6) 4

5 4.2 Algorth flow of the odule clent user request Request 1 queue Request 2 Request n Load balancer Weght calculaton odule weght request User Load nforaton Perodc feedback of the server Update Perodc feedback erver cluster 1 2 Request forwardng Request forwardng odule(wat new weght) New weght n Fg.1 Module algorth flow 4.3 Algorth to acheve the work flow chart Each ncong user request ust go through the followng process n order to select the approprate server,as shown n fg.2 start Y L()/L(su)<=a*W()/W(s u)? N provde servces All servers ust satsfy L()/L(su)>a*w()/W(s u)? N Calculate new weght Choose the rght one C()<Cax() N Y Add new server provde servces Fg.2 Algorth work flow chart 5

6 4.4 ulaton Experent and Result Analyss In order to verfy the basc perforance of the proved algorth, ths experent uses the networ k sulaton software OPNET Modeler 14.5 to sulate and test [9]. and wth the standard WLC algo rth coparson. OPNET provdes a three-ter odelng echans for botto-up odelng at th e process layer, node layer, and network layer [10], whle n the sulaton process t uses a dscrete e vent-drven sulaton echans that accurately analyze the perforance and behavor of cople x networks for data collecton and statstcs [11]. The network topology s shown n Fgure 3. Fg.3 Network topology dagra The server cluster conssts of four Web servers, usng 100M lne, respectvely server1, server2, server3, server4. The clent conssts of 12 subnets, each subnets contanng 45 user ternals. To verfy the algorth n the cluster syste, we use four dfferent of servers to ake up the server cluster. elect Eulaton et the HTTP applcaton n Applcaton_Confg to sulate an HTTP pcture and data load request scene. In order to splfy the operaton, the ntal paraeters k1, k2, k3 values were 0.5,0.3,0.2, the sulaton te s 30n, the update te s set to 10s. In ths experent, we anly observe the average response te,and the CPU utlzaton rato of the three algorths. Fg.4 The http te coparson Fg.5 WRR algorth for cpu utlzaton 6

7 Fg.6 ADWLC algorth for cpu utlzaton Fg.7 WLC algorth for cpu utlzaton It can be seen fro Fgure 4 n the HTTP request, ADWLC algorth average response te of 1.8s or so, than the WLC algorth and WRR effect s good. Fgure 5 shows that the CPU utlzaton of WRR algorth s relatvely scattered, the dfference s large; and through Fgure 6, we can see that the proved weghted nu nuber of connectons proved algorth CPU utlzaton s ore balanced, antaned at about 10%; 7 n the WLC algorth, each server cpu utlzaton whle antanng a sall gap, but stll not balanced, and the utlzaton rate s hgher; 5. Conclusons The core of the Web clusterng server s the load balancng algorth. Copare to the Weghted Mnu Connecton Nuber Algorth, the algorth put forward n ths paper consder the pact of real-te load on the load balance, and quote the perodc feedback echans to dynacally change the weghts, cobned wth the orgnal Weghted Mnu Connecton Nuber Algorth echans to deterne whch server to accept a new connecton request. Accordng to the sulaton results we can see, ths algorth can suffcently reduce the HTTP respondng te, reduce the delay of the server, balance the CPU utlzaton of each server. Of course, the algorth proposed n ths paper also has ts weakness, the ADWL algorth based on the proved nu nuber of connectons can only be acheved n the experental envronent, but not put nto use n the real network envronent yet. o, the next step s to put ths algorth on the actual network envronent to run the test, to verfy and prove ts perforance; econd, when the nuber of connectons between the server s large, how to re-adjust the newly added server node s the next step to consder the ssue. Acknowledgeents Natonal cence Fund subsdzed project ( ) References [1] Zhang X. Research on Dynac workload chedulng trategy of LV.Unversty of Jln [2] Zhou ongquan. An Iproved dynac load-balancng Algorth for Cluster[J].Coputer and odernzaton 2012(1): [3] HWANG T; JUNG N Dynac schedulng of web server cluster

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