{"id":36393,"date":"2019-10-31T22:11:24","date_gmt":"2019-10-31T19:11:24","guid":{"rendered":"https:\/\/prohoster.info\/blog\/failover-nas-gubit-perfektsionizm-i-len\/"},"modified":"2019-10-31T22:11:24","modified_gmt":"2019-10-31T19:11:24","slug":"failover-nas-gubit-perfektsionizm-i-len","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/administrirovanie\/failover-nas-gubit-perfektsionizm-i-len","title":{"rendered":"Failover: trp\u00edme perfekcionismem a\u2026 lenost\u00ed","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

V l\u00e9t\u011b tradi\u010dn\u011b kles\u00e1 jak aktivita nakupuj\u00edc\u00edch, tak intenzita zm\u011bn v infrastruktu\u0159e webov\u00fdch projekt\u016f, \u0159\u00edk\u00e1 n\u00e1m Kapit\u00e1n O\u010dividnost. Jen proto, \u017ee i IT odborn\u00edci, se st\u00e1v\u00e1, chod\u00ed na dovolenou. A CTO tak\u00e9. O to t\u011b\u017e\u0161\u00ed to maj\u00ed ti, kte\u0159\u00ed z\u016fst\u00e1vaj\u00ed na postu, ale te\u010f o tom to nen\u00ed: mo\u017en\u00e1 pr\u00e1v\u011b proto je l\u00e9to nejlep\u0161\u00edm obdob\u00edm na to, abychom v klidu p\u0159em\u00fd\u0161leli o st\u00e1vaj\u00edc\u00edm syst\u00e9mu z\u00e1lohov\u00e1n\u00ed a vytvo\u0159ili pl\u00e1n na jeho zlep\u0161en\u00ed. A v tom v\u00e1m bude u\u017eite\u010dn\u00fd zku\u0161enost Egora Andrejeva z AdminDivision<\/a><\/noindex>, o n\u011bm\u017e hovo\u0159il na konferenci Uptime den<\/a><\/noindex>.<\/i><\/p>\n

P\u0159i budov\u00e1n\u00ed z\u00e1lo\u017en\u00edch m\u00edst a p\u0159i z\u00e1lohov\u00e1n\u00ed existuje n\u011bkolik past\u00ed, do kter\u00fdch se m\u016f\u017eete dostat. A zapletat se do nich rozhodn\u011b nelze. A kaz\u00ed n\u00e1s na tom v\u0161em, stejn\u011b jako v mnoha jin\u00fdch ohledech, perfekcionismus a\u2026 lenost. Sna\u017e\u00edme se v\u0161echno d\u011blat perfektn\u011b, ale nen\u00ed t\u0159eba d\u011blat v\u0161echno dokonale! Je t\u0159eba ud\u011blat jen ur\u010dit\u00e9 v\u011bci, ale ud\u011blat je spr\u00e1vn\u011b, dot\u00e1hnout je do konce, aby norm\u00e1ln\u011b fungovaly. <\/p>\n

Failover nen\u00ed n\u011bjak\u00e1 vtipn\u00e1 z\u00e1le\u017eitost pro z\u00e1bavu; je to v\u011bc, kter\u00e1 by m\u011bla ud\u011blat p\u0159esn\u011b jednu v\u011bc \u2014 sn\u00ed\u017eit \u010das v\u00fdpadku, aby slu\u017eba a spole\u010dnost ztr\u00e1cely m\u00e9n\u011b pen\u011bz. A ve v\u0161ech metod\u00e1ch z\u00e1lohov\u00e1n\u00ed navrhuji p\u0159em\u00fd\u0161let v n\u00e1sleduj\u00edc\u00edm kontextu: kde jsou pen\u00edze?<\/p>\n

\"Failover:
\n<\/a><\/noindex>
\nPrvn\u00ed past<\/b>: kdy\u017e budujeme velk\u00e9 spolehliv\u00e9 syst\u00e9my a zab\u00fdv\u00e1me se z\u00e1lohov\u00e1n\u00edm \u2014 sni\u017eujeme po\u010det hav\u00e1ri\u00ed. To je stra\u0161liv\u00e9 myln\u00e9 p\u0159esv\u011bd\u010den\u00ed. Kdy\u017e se zab\u00fdv\u00e1me z\u00e1lohov\u00e1n\u00edm, pravd\u011bpodobn\u011b zvy\u0161ujeme po\u010det hav\u00e1ri\u00ed. A pokud v\u0161echno ud\u011bl\u00e1me spr\u00e1vn\u011b, sn\u00ed\u017e\u00edme celkov\u011b \u010das v\u00fdpadku. Hav\u00e1ri\u00ed bude v\u00edce, ale budou se d\u00edt s men\u0161\u00edmi ztr\u00e1tami. Co je z\u00e1lohov\u00e1n\u00ed? \u2014 to je zt\u00ed\u017een\u00ed syst\u00e9mu. Jak\u00e9koli zt\u00ed\u017een\u00ed \u2014 to je \u0161patn\u011b: p\u0159ich\u00e1z\u00ed n\u00e1m v\u00edce \u0161roubk\u016f, v\u00edce ozuben\u00fdch kol, zkr\u00e1tka v\u00edce prvk\u016f \u2014 a t\u00edm p\u00e1dem v\u011bt\u0161\u00ed \u0161ance na poruchu. A skute\u010dn\u011b se rozbij\u00ed. A budou se rozb\u00edjet \u010dast\u011bji. Jednoduch\u00fd p\u0159\u00edklad: dejme tomu, \u017ee m\u00e1me n\u011bjak\u00fd web, s PHP, MySQL. A je nal\u00e9hav\u011b pot\u0159eba ho z\u00e1lohovat. <\/p>\n

Tak\u017ee (c) Bereme druhou platformu, budujeme identick\u00fd syst\u00e9m... Slo\u017eitost se zdvojn\u00e1sobuje \u2014 m\u00e1me dv\u011b entity. A nav\u00edc p\u0159id\u00e1v\u00e1me ur\u010ditou logiku p\u0159enosu dat z jedn\u00e9 platformy na druhou \u2014 tedy replikaci dat, kop\u00edrov\u00e1n\u00ed statiky a tak d\u00e1le. Logika replikace je obvykle velmi slo\u017eit\u00e1, a proto m\u016f\u017ee b\u00fdt celkov\u00e1 slo\u017eitost syst\u00e9mu klidn\u011b 3, 5 nebo 10kr\u00e1t v\u011bt\u0161\u00ed. <\/p>\n

Druh\u00e1 past<\/b>: kdy\u017e budujeme opravdu velk\u00e9 slo\u017eit\u00e9 syst\u00e9my, fantaz\u00edrujeme, co vlastn\u011b chceme na konci z\u00edskat. Voil\u00e0: chceme superspolehliv\u00fd syst\u00e9m, kter\u00fd funguje bez jak\u00e9hokoli v\u00fdpadku, p\u0159ep\u00edn\u00e1 se za p\u016fl sekundy (a nejlep\u0161\u00ed by bylo okam\u017eit\u011b), a za\u010dneme realizovat sv\u00e9 sny. Ale tady je tak\u00e9 nuance: \u010d\u00edm krat\u0161\u00ed chceme dobu p\u0159epnut\u00ed, t\u00edm slo\u017eit\u011bj\u0161\u00ed logiku syst\u00e9mu mus\u00edme vytvo\u0159it. \u010c\u00edm slo\u017eit\u011bj\u0161\u00ed logiku budeme muset ud\u011blat, t\u00edm \u010dast\u011bji se syst\u00e9m bude porouch\u00e1vat. A m\u016f\u017eeme se dostat do velmi nep\u0159\u00edjemn\u00e9 situace: sna\u017e\u00edme se za ka\u017edou cenu zkr\u00e1tit dobu v\u00fdpadku, ale ve skute\u010dnosti to jenom komplikuje a kdy\u017e se n\u011bco nepovede, v\u00fdpadek nakonec bude del\u0161\u00ed. Zde si \u010dasto uv\u011bdom\u00edte: l\u00e9pe by bylo, kdybychom neprov\u00e1d\u011bli z\u00e1lohu. Bylo by lep\u0161\u00ed, kdyby to jedno fungovalo s jasnou dobou v\u00fdpadku. <\/p>\n

Jak se s t\u00edm d\u00e1 bojovat? Mus\u00edme p\u0159estat si lh\u00e1t, p\u0159estat si lichotit, \u017ee te\u010f budeme stav\u011bt kosmickou lo\u010f, ale adekv\u00e1tn\u011b pochopit, jak dlouho m\u016f\u017ee projekt vydr\u017eet. A na z\u00e1klad\u011b t\u00e9to maxim\u00e1ln\u00ed doby budeme vyb\u00edrat, jak\u00fdmi metodami zv\u00fd\u0161\u00edme spolehlivost na\u0161eho syst\u00e9mu. <\/p>\n

\"Failover:
\n
\nJe nejvy\u0161\u0161\u00ed \u010das na \u201ehistorie z j\u201c... samoz\u0159ejm\u011b ze \u017eivota. <\/p>\n

P\u0159\u00edklad \u010d\u00edslo jedna<\/h4>\n

\nP\u0159edstavte si vizitkovou str\u00e1nku trubkov\u00e9ho z\u00e1vodu \u010d. 1 m\u011bsta N. Na n\u00ed je naps\u00e1no obrovsk\u00fdmi p\u00edsmeny \u2014 TRUBKOV\u00dd Z\u00c1VOD \u010c. 1. Trochu n\u00ed\u017ee \u2014 slogan: \u201eNa\u0161e trubky jsou nejkulat\u011bj\u0161\u00ed trubky v N\u201c. A dole je telefonn\u00ed \u010d\u00edslo gener\u00e1ln\u00edho \u0159editele a jeho jm\u00e9no. Ch\u00e1pu, \u017ee je pot\u0159eba rezervace \u2014 to je opravdu d\u016fle\u017eit\u00e1 v\u011bc! Za\u010d\u00edn\u00e1me se zab\u00fdvat t\u00edm, z \u010deho se to skl\u00e1d\u00e1. Html-statika \u2014 tedy p\u00e1r obr\u00e1zk\u016f, kde gener\u00e1ln\u00ed \u0159editel toti\u017e sed\u00ed u stolu v saun\u011b se sv\u00fdm partnerem a diskutuj\u00ed o n\u011bjak\u00e9m dal\u0161\u00edm obchodu. Za\u010d\u00edn\u00e1me p\u0159em\u00fd\u0161let o dob\u011b ne\u010dinnosti. Napad\u00e1 n\u00e1s: m\u00edt to tam mus\u00ed b\u00fdt p\u011bt minut, maxim\u00e1ln\u011b. A tady ot\u00e1zka: kolik z na\u0161\u00ed str\u00e1nky bylo celkov\u011b prodej\u016f? Kolik kolik? Co znamen\u00e1 \u201enula\u201c? A znamen\u00e1 to: proto\u017ee v\u0161echny \u010dty\u0159i obchody za minul\u00fd rok gener\u00e1ln\u00ed uzav\u0159el u stejn\u00e9ho stolu, se stejn\u00fdmi lidmi, se kter\u00fdmi chod\u00ed do sauny a sed\u00ed za stolem. A uv\u011bdomujeme si, \u017ee i kdyby byla str\u00e1nka ne\u010dinn\u00e1 jeden den \u2014 nic hrozn\u00e9ho se nestane. <\/p>\n

Na z\u00e1klad\u011b t\u011bchto informac\u00ed m\u00e1me den na realizaci t\u00e9to z\u00e1le\u017eitosti. Za\u010d\u00edn\u00e1me p\u0159em\u00fd\u0161let o sch\u00e9matu rezervace. A vyb\u00edr\u00e1me ide\u00e1ln\u00ed sch\u00e9ma rezervace pro tento p\u0159\u00edklad: rezervaci nepot\u0159ebujeme. Tohle v\u0161echno se nastav\u00ed jak\u00fdmkoli administr\u00e1torem za p\u016fl hodiny s p\u0159est\u00e1vkami. Nainstalovat webov\u00fd server, um\u00edstit soubory \u2014 hotovo. Bude to fungovat. Na ni\u010dem nen\u00ed t\u0159eba d\u00e1vat pozor, ni\u010demu v\u011bnovat zvl\u00e1\u0161tn\u00ed pozornost. To znamen\u00e1, \u017ee z\u00e1v\u011br z prvn\u00edho p\u0159\u00edkladu je celkem jasn\u00fd: slu\u017eby, kter\u00e9 nen\u00ed pot\u0159eba rezervovat \u2014 rezervovat nen\u00ed pot\u0159eba.<\/p>\n

\"Failover:
\n<\/p>\n

P\u0159\u00edklad \u010d\u00edslo dv\u011b<\/h4>\n

\nBlog spole\u010dnosti: speci\u00e1ln\u011b \u0161kolen\u00ed lid\u00e9 tam p\u00ed\u0161\u00ed novinky, nap\u0159\u00edklad jsme se z\u00fa\u010dastnili takov\u00e9 v\u00fdstavy, a zde jsme vydali je\u0161t\u011b nov\u00fd produkt a tak d\u00e1le. P\u0159edstavme si, \u017ee jde o standardn\u00ed PHP s WordPressem, malou datab\u00e1zi a tro\u0161ku statiky. Samoz\u0159ejm\u011b, \u017ee m\u011b okam\u017eit\u011b napadne, \u017ee nesm\u00edme v \u017e\u00e1dn\u00e9m p\u0159\u00edpad\u011b ne\u010dinn\u011b le\u017eet \u2013 \"ne v\u00edce ne\u017e p\u011bt minut!\", to v\u0161echno. Ale poj\u010fme se zamyslet hloub\u011bji. Co ten blog d\u011bl\u00e1? Lid\u00e9 na n\u011bj chod\u00ed z Yandexu, z Googlu na n\u011bjak\u00e9 dotazy, organicky. Skv\u011bl\u00e9. A jak to souvis\u00ed se sales? Osv\u00edcen\u00ed: moc ne. Reklamn\u00ed provoz jde na hlavn\u00ed str\u00e1nku, kter\u00e1 je na jin\u00e9m serveru. Za\u010d\u00edn\u00e1me p\u0159em\u00fd\u0161let o sch\u00e9matu z\u00e1lohov\u00e1n\u00ed blogu. Opr\u00e1vn\u011bn\u011b by ho m\u011blo smysl zprovoznit b\u011bhem p\u00e1r hodin a na to by bylo dobr\u00e9 se p\u0159ipravit. Rozumn\u00e9 by bylo vz\u00edt server v jin\u00e9m datov\u00e9m centru, nainstalovat na n\u011bj prost\u0159ed\u00ed, tedy webov\u00fd server, PHP, WordPress, MySQL a nechat to tam 'le\u017eet' v klidu. V okam\u017eiku, kdy pochop\u00edme, \u017ee v\u0161e selhalo, je t\u0159eba ud\u011blat dv\u011b v\u011bci \u2013 obnovit dump mysql o velikosti 50 MB, co\u017e prob\u011bhne b\u011bhem minuty, a obnovit n\u011bjak\u00e9 mno\u017estv\u00ed obr\u00e1zk\u016f z z\u00e1lohy. To tak\u00e9 nen\u00ed \u017e\u00e1dn\u00e1 velk\u00e1 v\u011bc. T\u00edmto zp\u016fsobem se v\u0161echno zprovoz\u0148uje za p\u016fl hodiny. \u017d\u00e1dn\u00e9 replikace, nebo nedej bo\u017ee, automatick\u00e9 p\u0159ep\u00edn\u00e1n\u00ed. Z\u00e1v\u011br: to, co m\u016f\u017eeme rychle obnovit ze z\u00e1lohy, nen\u00ed pot\u0159eba z\u00e1lohovat. <\/p>\n

\"Failover:
\n<\/p>\n

P\u0159\u00edklad \u010d\u00edslo t\u0159i, o n\u011bco slo\u017eit\u011bj\u0161\u00ed<\/h4>\n

\nInternetov\u00fd obchod. PhP s open heart trochu upraven\u00fd, mysql s solidn\u00ed datab\u00e1z\u00ed. Docela hodn\u011b statiky (v\u017edy\u0165 v internetov\u00e9m obchod\u011b jsou kr\u00e1sn\u00e9 HD obr\u00e1zky a tak d\u00e1le), Redis pro relace a Elasticsearch pro vyhled\u00e1v\u00e1n\u00ed. Za\u010d\u00edn\u00e1me p\u0159em\u00fd\u0161let o dob\u011b v\u00fdpadku. A tady je samoz\u0159ejm\u011b z\u0159ejm\u00e9, \u017ee den, kdy bychom bezbolestn\u011b le\u017eeli, obchod nem\u016f\u017ee b\u00fdt. \u010c\u00edm d\u00e9le se le\u017e\u00ed, t\u00edm v\u00edce pen\u011bz ztr\u00e1c\u00edme. Je t\u0159eba se urychlit. A jak moc? P\u0159edpokl\u00e1d\u00e1m, \u017ee pokud budeme le\u017eet hodinu, nikdo se nezbl\u00e1zn\u00ed. Ano, n\u011bco ztrat\u00edme, ale za\u010dneme se sna\u017eit - bude to jen hor\u0161\u00ed. Ur\u010dujeme sch\u00e9ma, jak dlouho je v\u00fdpadek akceptov\u00e1n v hodin\u011b.<\/p>\n

Jak to v\u0161e lze rezervovat? Auto je v ka\u017ed\u00e9m p\u0159\u00edpad\u011b pot\u0159eba: hodina \u010dasu \u2014 to je dost m\u00e1lo. Mysql: zde ji\u017e pot\u0159ebujeme replikaci, \u017eivou replikaci, proto\u017ee za hodinu 100 GB do dumpu pravd\u011bpodobn\u011b nenask\u00e1\u010de. Statika, obr\u00e1zky: op\u011bt, za hodinu 500 GB m\u016f\u017ee nestihnout naskakovat. Tak\u017ee je lep\u0161\u00ed ihned zkop\u00edrovat obr\u00e1zky. Redis: tady to je zaj\u00edmav\u011bj\u0161\u00ed. V Redis jsou ulo\u017eeny relace \u2014 prost\u011b vz\u00edt a poh\u0159b\u00edt ho nem\u016f\u017eeme. Proto\u017ee to by nebylo p\u0159\u00edli\u0161 dobr\u00e9: v\u0161ichni u\u017eivatel\u00e9 by byli odhl\u00e1\u0161eni, ko\u0161\u00edky vypr\u00e1zdn\u011bny a tak d\u00e1le. Lid\u00e9 by museli znovu zad\u00e1vat sv\u00e9 p\u0159ihla\u0161ovac\u00ed \u00fadaje a mnoho z nich by se mohlo odhl\u00e1sit a n\u00e1kup nedokon\u010dit. Op\u011bt, konverze by klesla. Na druhou stranu, Redis je p\u0159\u00edmo aktu\u00e1ln\u00ed, s posledn\u00edmi p\u0159ihl\u00e1\u0161en\u00fdmi u\u017eivateli, asi tak\u00e9 nen\u00ed pot\u0159eba. A dobr\u00fdm kompromisem \u2014 vz\u00edt Redis a obnovit ho z z\u00e1lohy, v\u010derej\u0161\u00ed, nebo, pokud ji m\u00e1te ka\u017edou hodinu, \u2014 z hodinov\u00e9. Na\u0161t\u011bst\u00ed obnova z z\u00e1lohy je kop\u00edrov\u00e1n\u00ed jednoho souboru. A nejzaj\u00edmav\u011bj\u0161\u00ed p\u0159\u00edb\u011bh \u2014 to je Elasticsearch. Kdo kdy z\u0159izoval replikaci MySQL? Kdo kdy z\u0159izoval replikaci Elasticsearch? A u koho to potom norm\u00e1ln\u011b fungovalo? K \u010demu t\u00edm m\u00ed\u0159\u00edm: vid\u00edme v na\u0161em syst\u00e9mu n\u011bjakou entitu. Vypad\u00e1 to jako u\u017eite\u010dn\u00e9 \u2014 ale je to slo\u017eit\u00e9.
\nSlo\u017eit\u00fd v tom smyslu, \u017ee na\u0161i kolegov\u00e9 in\u017een\u00fd\u0159i nemaj\u00ed zku\u0161enosti s jeho pou\u017eit\u00edm. Bu\u010f maj\u00ed negativn\u00ed zku\u0161enosti, nebo si uv\u011bdomujeme, \u017ee jde o relativn\u011b novou technologii s nuance nebo nedostatky. P\u0159em\u00fd\u0161l\u00edme\u2026 Sakra, elastic je tak\u00e9 obrovsk\u00fd, jeho obnoven\u00ed z z\u00e1lohy trv\u00e1 dlouho, co s t\u00edm d\u011blat? Ch\u00e1peme, \u017ee elastic je v na\u0161em p\u0159\u00edpad\u011b pou\u017e\u00edv\u00e1n pro vyhled\u00e1v\u00e1n\u00ed. A jak prod\u00e1v\u00e1 n\u00e1\u0161 internetov\u00fd obchod? Jdeme k market\u00e9r\u016fm, pt\u00e1me se, odkud lid\u00e9 p\u0159ich\u00e1zej\u00ed. Odpov\u00eddaj\u00ed: \u201e90 % p\u0159ich\u00e1z\u00ed p\u0159\u00edmo z Yandex.Market do karty produktu\u201c. A bu\u010f nakupuj\u00ed, nebo ne. N\u00e1sledn\u011b vyhled\u00e1n\u00ed pot\u0159ebuje 10 % u\u017eivatel\u016f. A udr\u017eov\u00e1n\u00ed replikace elasticu, zejm\u00e9na mezi r\u016fzn\u00fdmi datov\u00fdmi centry v r\u016fzn\u00fdch z\u00f3n\u00e1ch, \u2013 to m\u00e1 opravdu spoustu nuanc\u00ed. Jak\u00fd je v\u00fdstup? Bereme elastic na rezervovan\u00e9 platform\u011b a nic s n\u00edm ned\u011bl\u00e1me. Pokud se situace prot\u00e1hne, mo\u017en\u00e1 ho n\u011bkdy pozd\u011bji zvedneme, ale to nen\u00ed jist\u00e9. Vlastn\u011b, z\u00e1v\u011br je plus minus stejn\u00fd: slu\u017eby, kter\u00e9 nemaj\u00ed vliv na pen\u00edze, znovu nerezervujeme. Aby sch\u00e9ma z\u016fstalo jednodu\u0161\u0161\u00ed.<\/p>\n

\"Failover:
\n<\/p>\n

P\u0159\u00edklad \u010d\u00edslo \u010dty\u0159i, je\u0161t\u011b slo\u017eit\u011bj\u0161\u00ed.<\/h4>\n

\nIntegrator: prodej kv\u011btin, vol\u00e1n\u00ed taxislu\u017eby, prodej zbo\u017e\u00ed, zkr\u00e1tka cokoli. V\u00e1\u017e\u00ed z\u00e1le\u017eitost, kter\u00e1 pracuje 24\/7 pro velk\u00fd po\u010det u\u017eivatel\u016f. S plnohodnotnou zaj\u00edmavou technologi\u00ed, kde jsou zaj\u00edmav\u00e9 datab\u00e1ze, \u0159e\u0161en\u00ed, vysok\u00e9 zat\u00ed\u017een\u00ed, a co je nejd\u016fle\u017eit\u011bj\u0161\u00ed, le\u017eet mu v\u00edce ne\u017e 5 minut opravdu bol\u00ed. Nejen a nejen proto, \u017ee lid\u00e9 nenakoup\u00ed, ale proto\u017ee lid\u00e9 uvid\u00ed, \u017ee tato v\u011bc nefunguje, zklamou a mo\u017en\u00e1 se u\u017e nikdy nevr\u00e1t\u00ed. <\/p>\n

Dob\u0159e. P\u011bt minut. Co s t\u00edm budeme d\u011blat? V tomto p\u0159\u00edpad\u011b, dosp\u011bl\u00fdm zp\u016fsobem, za v\u0161echny pen\u00edze budujeme skute\u010dnou rezervovanou plochu, s replikac\u00ed v\u0161eho a v\u0161echo, a mo\u017en\u00e1 dokonce automatizujeme maxim\u00e1ln\u011b p\u0159epnut\u00ed na tuto plochu. A k tomu nesm\u00edme zapomenout na jednu d\u016fle\u017eitou v\u011bc: toti\u017e napsat pravidla pro p\u0159epnut\u00ed. Pravidla, i kdy\u017e m\u00e1te v\u0161echno a v\u0161echo automatizovan\u00e9, mohou b\u00fdt velmi jednoduch\u00e1. Nap\u0159\u00edklad \u201espustit takov\u00fdto sc\u00e9n\u00e1\u0159 ansible\u201c, \u201ev route 53 za\u0161krtnout takovou mo\u017enost\u201c a tak d\u00e1le \u2014 ale m\u011blo by to b\u00fdt n\u011bjak\u00fd p\u0159esn\u00fd seznam krok\u016f. <\/p>\n

A zd\u00e1 se, \u017ee je v\u0161e jasn\u00e9. P\u0159epnout replikaci \u2014 trivi\u00e1ln\u00ed \u00fakol, bu\u010f se p\u0159epne sama. P\u0159epsat dom\u00e9nov\u00e9 jm\u00e9no v DNS \u2014 to sam\u00e9. Probl\u00e9m je v tom, \u017ee kdy\u017e takov\u00fd projekt spadne, za\u010dne panika, a i ti nejzku\u0161en\u011bj\u0161\u00ed admini j\u00ed mohou podl\u00e9hat. Bez jasn\u00e9ho n\u00e1vodu \u201eotev\u0159i termin\u00e1l, p\u0159ejdi sem, adresa na\u0161eho serveru je st\u00e1le takov\u00e1\u201c je t\u011b\u017ek\u00e9 dr\u017eet p\u011btiminutov\u00fd \u010dasov\u00fd limit na z\u00e1chranu. A nav\u00edc, kdy\u017e tento p\u0159edpis pou\u017e\u00edv\u00e1me, je snadn\u00e9 zafixovat n\u011bjak\u00e9 zm\u011bny v infrastruktu\u0159e, nap\u0159\u00edklad \u2014 a odpov\u00eddaj\u00edc\u00edm zp\u016fsobem zm\u011bnit p\u0159edpis.
\nNo, pokud je syst\u00e9m rezervace velmi slo\u017eit\u00fd a v n\u011bjak\u00e9m okam\u017eiku ud\u011bl\u00e1me chybu, m\u016f\u017eeme zni\u010dit i na\u0161i z\u00e1lo\u017en\u00ed lokalitu, a nav\u00edc prom\u011bnit data v d\u00fdni na obou lokalit\u00e1ch \u2014 to bude opravdu smutn\u00e9. <\/p>\n

\"Failover:
\n<\/p>\n

P\u0159\u00edklad \u010d\u00edslo p\u011bt, naprost\u00fd hardcore<\/h4>\n

\nMezin\u00e1rodn\u00ed slu\u017eba se stovkami milion\u016f u\u017eivatel\u016f po cel\u00e9m sv\u011bt\u011b. V\u0161echny \u010dasov\u00e1 p\u00e1sma, kter\u00e1 existuj\u00ed, highload na maximum, nesm\u00ed b\u00fdt \u017e\u00e1dn\u00e9 v\u00fdpadky. Minuta \u2014 a bude smutno. Co d\u011blat? Z\u00e1lohovat, op\u011bt naplno. Ud\u011blali jsme v\u0161e, co jsem \u0159\u00edkal v p\u0159edchoz\u00edm p\u0159\u00edkladu, a je\u0161t\u011b o kousek v\u00edc. Ide\u00e1ln\u00ed sv\u011bt, a na\u0161e infrastruktura \u2014 to je podle v\u0161ech definic devops IaaC. To znamen\u00e1, \u017ee v\u0161e je v\u016fbec v gitu, a jen stiskni tla\u010d\u00edtko. <\/p>\n

Co chyb\u00ed? Jedno \u2014 cvi\u010den\u00ed. Bez nich to nejde. Zd\u00e1 se, \u017ee m\u00e1me v\u0161e perfektn\u00ed, v\u0161e je pod kontrolou. Stiskneme tla\u010d\u00edtko, v\u0161echno se d\u011bje. I kdy\u017e tomu tak je \u2014 a my v\u00edme, \u017ee to tak nen\u00ed \u2014 n\u00e1\u0161 syst\u00e9m interaguje s n\u011bjak\u00fdmi jin\u00fdmi syst\u00e9my. Nap\u0159\u00edklad, je to DNS od Route 53, S3 \u00falo\u017ei\u0161t\u011b, integrace s n\u011bjak\u00fdmi API. V\u0161e v tomto hypotetick\u00e9m experimentu nem\u016f\u017eeme p\u0159edv\u00eddat. A dokud re\u00e1ln\u011b nevytrhneme vyp\u00edna\u010d \u2014 nezjist\u00edme, jestli to bude fungovat nebo ne. <\/p>\n

\"Failover:
\n
\nNa tom to asi je v\u0161e. Nezleniv\u011bte a nep\u0159eh\u00e1n\u011bjte to. A a\u0165 v\u00e1s prov\u00e1z\u00ed uptime!
\n
Zdroj: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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