CS514: Intermediate Course in Operating Systems. Recipe for a group communication system. Role of GMS. Group membership service

Transcription

1 CS514: Inemediae Coue in Oeaing Syem Pofeo Ken Biman Vivek Vihnumuhy: TA Reminde: Gou Communicaion u Teminology: gou ceae, view, join wih ae anfe, mulica, clien-o-gou communicaion Thi i he dynamic membehi model: ocee come & go Recie fo a gou communicaion yem Back one ie hell Build a evice ha can ack gou membehi and eo view change Peae 2 cu of baic ie filling Develo a imle faul-olean mulica oocol Add flavoing of you choice Exend he mulica oocol o ovide deied delivey odeing guaanee Fill ie hell, chill, and eve Deign an end-ue API o oolki. Clien will eve hemelve, wih vaiou goal Role of GMS We ll add a new yem evice o ou diibued yem, like he Inene DNS bu wih a new ole I job i o ack membehi of gou To join a gou a oce will ak he GMS The GMS will alo monio membe and can ue hi o do hem fom a gou And i will eo membehi change Gou icue wih GMS Gou membehi evice GMS GMS T o eond: GMS: Wha Gou i cuen X ceaed membehi wih you a P eue: he I fo wih only gou membe X? o join o ceae gou X. GMS noice ha Q join, now X = {,}. Since ha failed (o decide o leave) GMS o T: X i = he {} olde io join membe, i doe a ae anfe o u Run on ome enible lace, like he eve hoing you DNS Take a inu: Poce join even Poce leave even Aaen failue Ouu: Membehi view fo gou() o which hoe ocee belong Seen by he oocol libay ha he gou membe ae uing fo communicaion uo

2 Iue? Gou icue wih GMS The evice ielf need o be faulolean Ohewie ou enie yem could be ciled by a ingle failue! So we ll un wo o hee coie of i Hence Gou Membehi Sevice (GMS) mu un ome fom of oocol (GMP) GMS Gou icue wih GMS Aoach GMS 0 GMS 1 GMS 2 Le a by focuing on how GMS ack i own membehi. Since i can ju ak he The GMS i a GMS gou o oo. do hi We ll i need build i o fi have and a ecial hen will ue oocol i when fo building hi uoe. eliable Bu mulica only he GMS un hi ecial oocol. oocol, ince ohe ocee ju ely on he GMS o do hi job In fac i will end u uing hoe eliable mulica oocol o elicae membehi infomaion fo ohe gou ha ely on i We ll aume ha GMS ha membe {,,} a ime Deignae he olde of hee a he oocol leade To iniiae a change in GMS membehi, leade will un he GMP Ohe can un he GMP; hey eo even o he leade GMP examle Examle: Iniially, GMS coni of {,,} Then i believed o have cahed Failue deecion: may make miake Recall ha failue ae had o diinguih fom newok delay So we acce ik of miake If i unning a oocol o exclude becaue ha failed, all ocee ha hea fom will cu channel o Avoid meage fom he dead mu ejoin o aiciae in GMS again

3 Baic GMP Someone eo ha ha failed Leade (oce ) un a 2-hae commi oocol Announce a ooed new GMS view Exclude, o migh add ome membe who ae joining, o could do boh a once Wai unil a majoiy of membe of cuen view have voed ok Then commi he change V 0 = {,,} GMP examle Pooed V 1 = {,} OK Commi V 1 V 1 = {,} Pooe new view: {,} [-] Need majoiy conen: ielf, lu one moe ( cuen view had 3 membe) Can add membe a he ame ime Secial concen? Wha if omeone doen eond? P can oleae failue of a minoiy of membe of he cuen view New fi-ound ovela i commi: Commi ha ha lef. Pooe add and do P mu wai if i can conac a majoiy Avoid ik of aiioning Wha if leade fail? Hee we do a 3-hae oocol New leade idenifie ielf baed on age anking (olde uviving oce) I un an inuiy hae The adoed leade ha died. Did he ay anyhing o you befoe aing away? Noe ha hi caue aician o cu connecion o he adoed eviou leade Then un nomal 2-hae oocol bu eminae any ineued view change leade had iniiaed V 0 = {,,} GMP examle Inuie [-] OK: nohing wa ending Pooed V 1 = {,} New leade fi end an inuiy Then ooe new view: {,} [-] Need majoiy conen: ielf, lu one moe ( cuen view had 3 membe) Again, can add membe a he ame ime OK Commi V 1 V 1 = {,} Poeie of GMP We end u wih a ingle evice haed by he enie yem In fac evey oce can aiciae Bu moe ofen we ju deignae a few ocee and hey un he GMP Tyically he GMS un he GMP and alo ue elicaed daa o ack membehi of ohe gou

4 Ue of GMS A oce, no in he GMS, wan o join gou Uon309_au I end a eue o he GMS GMS udae he membehi of gou Uon309_au o add Reo he new view o he cuen membe of he gou, and o Begin o monio healh Pocee and u uing a GMS u The GMS conain,, (and lae, ) Pocee and u wan o fom ome ohe gou, bu ue he GMS o manage membehi on hei behalf We have ou ie hell Now we ve go a gou membehi evice ha eo idenical view o all membe, ack healh Can we build a eliable mulica? Uneliable mulica Suoe ha o end a mulica, a oce ju ue an uneliable oocol Peha IP mulica Peha UDP oin-o-oin Peha TCP ome meage migh ge doed. If o i evenually find ou and eend hem (vaiou oion fo how o do i) Concen if ende cahe Peha i en ome meage and only one oce ha een i We would efe o enue ha All eceive, in cuen view Receive any meage ha any eceive eceive (unle he ende and all eceive cah, eaing evidence ) An ineued mulica A meage fom o wa doed Since ha cahed, i won be een

5 Fluh oocol We ay ha a meage i unable if ome eceive ha i bu (eha) ohe don Fo examle, meage i unable a oce If fail we wan o fluh unable meage ou of he yem How o do hi? Eay oluion: all-o-all echo When a new view i eoed All ocee echo any unable meage on all channel on which hey haven eceived a coy of hoe meage A fluy of O(n 2 ) meage Noe: mu do hi fo all meage, no ju hoe fom he failed oce. Thi i becaue moe failue could haen in fuue An ineued mulica had an unable meage, o i echoed i when i aw he new view Even odeing We hould fi delive he mulica o he alicaion laye and hen eo he new view Thi way all elica ee he ame meage deliveed in he ame view Some call hi view ynchony Sae anfe A he inan he new view i eoed, a oce aleady in he gou make a checkoin Send oin-o-oin o new membe() I (hey) iniialize fom he checkoin Sae anfe and eliable mulica Afe e-odeing, i look like each mulica i eliably deliveed in he ame view a each eceive Noe: if ende and all eceive fail, unable meage can be eaed even afe delivey o an alicaion Thi i a ice we ay o gain highe eed

6 Wha abou odeing? I i ivial o make ou oocol FIFO w ohe meage fom ame ende If we ju numbe meage fom each ende, hey will ay in ode Concuen meage ae unodeed If en by diffeen ende, meage can be deliveed in diffeen ode a diffeen eceive Thi i he oocol called fbca Peview of coming aacion Nex ime we ll add iche odeing oeie Gou communicaion lafom ofen offe a ange Idea i ha develoe will ick he cheae oluion ha mee need of a given ue