{"id":52324,"date":"2019-11-06T00:00:00","date_gmt":"2019-11-05T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/hvatit-ispolzovat-smehotvorno-malyj-ttl-dlya-dns"},"modified":"2021-01-02T13:04:14","modified_gmt":"2021-01-02T11:04:14","slug":"hvatit-ispolzovat-smehotvorno-malyj-ttl-dlya-dns","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/administrirovanie\/hvatit-ispolzovat-smehotvorno-malyj-ttl-dlya-dns","title":{"rendered":"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>N\u00edzk\u00e1 latence DNS je kl\u00ed\u010dov\u00fdm faktorem pro rychl\u00e9 fungov\u00e1n\u00ed internetu. Abychom ji minimalizovali, je d\u016fle\u017eit\u00e9 pe\u010dliv\u011b vyb\u00edrat DNS servery a <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/DNSCrypt\/dnscrypt-resolvers\/blob\/master\/v2\/relays.md\">anonymn\u00ed rel\u00e9<\/a><\/noindex>. Ale nejprve je t\u0159eba zbavit se zbyte\u010dn\u00fdch dotaz\u016f.<\/p>\n<p>Proto byl DNS p\u016fvodn\u011b navr\u017een jako siln\u011b cachovan\u00fd protokol. Spr\u00e1vci z\u00f3n nastavuj\u00ed \u010das \u017eivota (TTL) pro jednotliv\u00e9 z\u00e1znamy, a resolver'y tuto informaci pou\u017e\u00edvaj\u00ed k ukl\u00e1d\u00e1n\u00ed z\u00e1znam\u016f do pam\u011bti, aby se vyhnuli zbyte\u010dn\u00e9mu provozu.<\/p>\n<p>Je caching efektivn\u00ed? P\u0159ed p\u00e1r lety jsem provedl mal\u00fd v\u00fdzkum, kter\u00fd uk\u00e1zal, \u017ee to nen\u00ed dokonal\u00e9. Poj\u010fme se pod\u00edvat na aktu\u00e1ln\u00ed stav.<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><br \/>\nPro shrom\u00e1\u017ed\u011bn\u00ed informac\u00ed jsem upravil <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/jedisct1\/encrypted-dns-server\">Encrypted DNS Server<\/a><\/noindex> pro zachov\u00e1n\u00ed hodnoty TTL pro odpov\u011b\u010f. Ta je ur\u010dena jako minim\u00e1ln\u00ed TTL jeho z\u00e1znam\u016f pro ka\u017ed\u00fd p\u0159\u00edchoz\u00ed dotaz. To poskytuje dobr\u00fd p\u0159ehled o rozlo\u017een\u00ed TTL skute\u010dn\u00e9ho provozu a tak\u00e9 zohled\u0148uje popularitu jednotliv\u00fdch dotaz\u016f. Upraven\u00e1 verze serveru fungovala n\u011bkolik hodin.<\/p>\n<p>V\u00fdsledn\u00e1 datov\u00e1 sada obsahuje 1&nbsp;583&nbsp;579 z\u00e1znam\u016f (name, qtype, TTL, timestamp). Zde je celkov\u00e9 rozlo\u017een\u00ed TTL (osa X p\u0159edstavuje TTL v sekund\u00e1ch):<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/ce19a1ceb07e1fd2f3b2284f86271eac.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Pokud nepo\u010d\u00edt\u00e1me nepatrn\u00fd vrchol na 86&nbsp;400 (v\u011bt\u0161inou pro z\u00e1znamy SOA), je z\u0159ejm\u00e9, \u017ee TTL jsou v n\u00edzk\u00e9m rozmez\u00ed. Pod\u00edvejme se bl\u00ed\u017ee:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/abbe48952b616e1c5bdb18c2dc103dc7.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Dob\u0159e, TTL p\u0159es 1 hodinu jsou statisticky nev\u00fdznamn\u00e9. Tak\u017ee se zam\u011b\u0159me na rozsah 0\u22123600:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/f8a88267e1868a55d9234f66ad8c5dee.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>V\u011bt\u0161ina TTL od 0 do 15 minut:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/aab650c806097513a5924e5262211ea5.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Drtiv\u00e1 v\u011bt\u0161ina od 0 do 5 minut:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/736af4b33b745fb0d5070200fa511426.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>To nen\u00ed moc dobr\u00e9.<\/p>\n<p>Kumulativn\u00ed rozlo\u017een\u00ed d\u011bl\u00e1 probl\u00e9m je\u0161t\u011b z\u0159eteln\u011bj\u0161\u00edm:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/a3a4f03188dd6dbbf4558076b827f6a5.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>V polovin\u011b DNS odpov\u011bd\u00ed TTL \u010din\u00ed 1 minutu nebo m\u00e9n\u011b, a u t\u0159\u00ed \u010dtvrtin&nbsp;\u2014 5 minut nebo m\u00e9n\u011b.<\/p>\n<p>Ale po\u010dkejte, ve skute\u010dnosti je to je\u0161t\u011b hor\u0161\u00ed. V\u017edy\u0165 to jsou TTL od autoritativn\u00edch server\u016f. Av\u0161ak klientsk\u00e9 resolvery (nap\u0159. routery, m\u00edstn\u00ed cache) z\u00edsk\u00e1vaj\u00ed TTL od nad\u0159azen\u00fdch resolver\u016f, a ten se ka\u017edou sekundu zkracuje.<\/p>\n<p>Tak\u017ee klient m\u016f\u017ee ve skute\u010dnosti pou\u017e\u00edvat ka\u017ed\u00fd z\u00e1znam v pr\u016fm\u011bru polovinu p\u016fvodn\u00edho TTL, po \u010dem\u017e ode\u0161le nov\u00fd dotaz.<\/p>\n<p>Mo\u017en\u00e1, \u017ee tyto velmi n\u00edzk\u00e9 TTL se t\u00fdkaj\u00ed pouze neobvykl\u00fdch dotaz\u016f, nikoli popul\u00e1rn\u00edch webov\u00fdch str\u00e1nek a API? Poj\u010fme se pod\u00edvat:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/2680f9669a90f449a593edcc84ca0dc8.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Osa X&nbsp;\u2014 to je TTL, osa Y&nbsp;\u2014 popularita dotaz\u016f.<\/p>\n<p>Bohu\u017eel, nejpopul\u00e1rn\u011bj\u0161\u00ed dotazy jsou tak\u00e9 ty, kter\u00e9 se nejh\u016f\u0159e cachuj\u00ed.<\/p>\n<p>P\u0159ibl\u00ed\u017e\u00edme:<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/c670382b195169779743f43fd7b15827.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Verdikt: je to skute\u010dn\u011b \u0161patn\u00e9. U\u017e to bylo \u0161patn\u00e9, a te\u010f je to je\u0161t\u011b hor\u0161\u00ed. DNS caching se stal t\u00e9m\u011b\u0159 k ni\u010demu. Proto\u017ee st\u00e1le m\u00e9n\u011b lid\u00ed pou\u017e\u00edv\u00e1 DNS resolver sv\u00e9ho poskytovatele (z v\u00e1\u017en\u00fdch d\u016fvod\u016f), zpo\u017ed\u011bn\u00ed se st\u00e1v\u00e1 v\u00edce viditeln\u00fdm.<\/p>\n<p>DNS caching se stal u\u017eite\u010dn\u00fdm pouze pro obsah, kter\u00fd nikdo nenav\u0161t\u011bvuje.<\/p>\n<p>Tak\u00e9 m\u011bjte na pam\u011bti, \u017ee software m\u016f\u017ee <noindex><a rel=\"nofollow\" href=\"https:\/\/00f.net\/2011\/11\/17\/how-long-does-a-dns-ttl-last\/\">r\u016fzn\u011b<\/a><\/noindex> interpretovat n\u00edzk\u00e9 TTL.<\/p>\n<h1>Pro\u010d tomu tak je?<\/h1>\n<p>Pro\u010d je pro DNS z\u00e1znamy nastavena tak n\u00edzk\u00e1 TTL?<\/p>\n<ul>\n<li>Zastaral\u00e9 load balancery z\u016fstaly s v\u00fdchoz\u00edmi nastaven\u00edmi.<\/li>\n<li>Roz\u0161\u00ed\u0159ily se m\u00fdty, \u017ee DNS vyva\u017eov\u00e1n\u00ed z\u00e1t\u011b\u017ee z\u00e1vis\u00ed na TTL (to nen\u00ed pravda&nbsp;\u2014 od dob Netscape Navigator klienti n\u00e1hodn\u011b vyb\u00edraj\u00ed IP adresu z mno\u017einy RR a transparentn\u011b se pokou\u0161ej\u00ed o jinou, pokud se nemohou p\u0159ipojit)<\/li>\n<li>Administr\u00e1to\u0159i cht\u011bj\u00ed aplikovat zm\u011bny okam\u017eit\u011b, proto\u017ee je to tak jednodu\u0161\u0161\u00ed pro pl\u00e1nov\u00e1n\u00ed.<\/li>\n<li>Administr\u00e1tor DNS serveru nebo load balancer vid\u00ed svou \u00falohu v efektivn\u00edm nasazen\u00ed konfigurace, kterou u\u017eivatel\u00e9 po\u017eaduj\u00ed, nikoli v zrychlov\u00e1n\u00ed webov\u00fdch str\u00e1nek a slu\u017eeb.<\/li>\n<li>N\u00edzk\u00e9 TTL poskytuj\u00ed du\u0161evn\u00ed klid.<\/li>\n<li>Lid\u00e9 p\u016fvodn\u011b nastavuj\u00ed n\u00edzk\u00e9 TTL pro testov\u00e1n\u00ed a pak na to zapom\u00ednaj\u00ed zm\u011bnit.<\/li>\n<\/ul>\n<p>Nezahrnul jsem do seznamu 'zpracov\u00e1n\u00ed selh\u00e1n\u00ed', proto\u017ee to je st\u00e1le m\u00e9n\u011b aktu\u00e1ln\u00ed. Pokud je t\u0159eba p\u0159esm\u011brovat u\u017eivatele do jin\u00e9 s\u00edt\u011b pouze pro zobrazen\u00ed chybov\u00e9 str\u00e1nky, kdy\u017e je v\u0161e ostatn\u00ed \u00fapln\u011b rozbit\u00e9, pravd\u011bpodobn\u011b je p\u0159ijateln\u00e1 prodleva del\u0161\u00ed ne\u017e 1 minuta.<\/p>\n<p>Krom\u011b toho minutov\u00e9 TTL znamen\u00e1, \u017ee pokud budou autoritativn\u00ed DNS servery zablokov\u00e1ny v\u00edce ne\u017e na 1 minutu, nikdo jin\u00fd nebude schopen p\u0159istupovat k z\u00e1visl\u00fdm slu\u017eb\u00e1m. A redundance nepom\u016f\u017ee, pokud je p\u0159\u00ed\u010dinou chyba konfigurace nebo hack. Na druhou stranu, p\u0159i rozumn\u00fdch TTL mnoho klient\u016f st\u00e1le pou\u017eije p\u0159edchoz\u00ed konfiguraci a nikdy si ni\u010deho nev\u0161imnou.<\/p>\n<p>Na n\u00edzk\u00fdch TTL se v\u00fdrazn\u011b pod\u00edlej\u00ed CDN slu\u017eby a load balancery, zvl\u00e1\u0161t\u011b kdy\u017e spojuj\u00ed CNAME s mal\u00fdmi TTL a z\u00e1znamy s podobn\u011b mal\u00fdmi (ale nez\u00e1visl\u00fdmi) TTL:<\/p>\n<pre>$ drill raw.githubusercontent.com\nraw.githubusercontent.com.\t9\tIN\tCNAME\tgithub.map.fastly.net.\ngithub.map.fastly.net.\t20\tIN\tA\t151.101.128.133\ngithub.map.fastly.net.\t20\tIN\tA\t151.101.192.133\ngithub.map.fastly.net.\t20\tIN\tA\t151.101.0.133\ngithub.map.fastly.net.\t20\tIN\tA\t151.101.64.133<\/pre>\n<p>Kdykoli vypr\u0161\u00ed CNAME nebo n\u011bkter\u00e1 z A z\u00e1znam\u016f, je nutn\u00e9 odeslat nov\u00fd dotaz. Oba maj\u00ed TTL 30 sekund, ale neodpov\u00eddaj\u00ed si. Skute\u010dn\u00fd pr\u016fm\u011brn\u00fd TTL bude 15 sekund.<\/p>\n<p>Ale po\u010dkejte! Je to je\u0161t\u011b hor\u0161\u00ed. N\u011bkter\u00e9 resolvery se v t\u00e9to situaci se dv\u011bma propojen\u00fdmi n\u00edzk\u00fdmi TTL chovaj\u00ed velmi \u0161patn\u011b:<\/p>\n<pre>$ drill raw.githubusercontent.com @4.2.2.2\nraw.githubusercontent.com.\t1\tIN\tCNAME\tgithub.map.fastly.net.\ngithub.map.fastly.net.\t1\tIN\tA\t151.101.16.133<\/pre>\n<p>Resolver Level3 pravd\u011bpodobn\u011b b\u011b\u017e\u00ed na BIND. Pokud budete pokra\u010dovat v odes\u00edl\u00e1n\u00ed tohoto dotazu, v\u017edy se vr\u00e1t\u00ed TTL rovn\u00e9 1. V podstat\u011b, <code>raw.githubusercontent.com<\/code> nikdy nen\u00ed mezipam\u011b\u0165.<\/p>\n<p>Tady je dal\u0161\u00ed p\u0159\u00edklad takov\u00e9 situace s velmi popul\u00e1rn\u00ed dom\u00e9nou:<\/p>\n<pre>$ drill detectportal.firefox.com @1.1.1.1\ndetectportal.firefox.com.\t25\tIN\tCNAME\tdetectportal.prod.mozaws.net.\ndetectportal.prod.mozaws.net.\t26\tIN\tCNAME\tdetectportal.firefox.com-v2.edgesuite.net.\ndetectportal.firefox.com-v2.edgesuite.net.\t10668\tIN\tCNAME\ta1089.dscd.akamai.net.\na1089.dscd.akamai.net.\t10\tIN\tA\t104.123.50.106\na1089.dscd.akamai.net.\t10\tIN\tA\t104.123.50.88<\/pre>\n<p>Nejm\u00e9n\u011b t\u0159i CNAME z\u00e1znamy. Ach. U jednoho je slu\u0161n\u00fd TTL, ale to je naprosto k ni\u010demu. U dal\u0161\u00edch CNAME je prvotn\u00ed TTL 60 sekund, ale pro dom\u00e9ny <code>akamai.net<\/code> maxim\u00e1ln\u00ed TTL \u010din\u00ed 20 sekund a ani jeden z nich nen\u00ed ve f\u00e1zi.<\/p>\n<p>Co dom\u00e9ny, kter\u00e9 neust\u00e1le dotazuj\u00ed za\u0159\u00edzen\u00ed Apple?<\/p>\n<pre>$ drill 1-courier.push.apple.com @4.2.2.2\n1-courier.push.apple.com.\t1253\tIN\tCNAME\t1.courier-push-apple.com.akadns.net.\n1.courier-push-apple.com.akadns.net.\t1\tIN\tCNAME\tgb-courier-4.push-apple.com.akadns.net.\ngb-courier-4.push-apple.com.akadns.net.\t1\tIN\tA\t17.57.146.84\ngb-courier-4.push-apple.com.akadns.net.\t1\tIN\tA\t17.57.146.85<\/pre>\n<p>Stejn\u00fd probl\u00e9m jako u Firefoxu a TTL v\u011bt\u0161inu \u010dasu uv\u00edzne na 1 sekund\u011b p\u0159i pou\u017eit\u00ed resolveru Level3.<\/p>\n<p>Dropbox?<\/p>\n<pre>$ drill client.dropbox.com @8.8.8.8\nclient.dropbox.com.\t7\tIN\tCNAME\tclient.dropbox-dns.com.\nclient.dropbox-dns.com.\t59\tIN\tA\t162.125.67.3\n\n$ drill client.dropbox.com @4.2.2.2\nclient.dropbox.com.\t1\tIN\tCNAME\tclient.dropbox-dns.com.\nclient.dropbox-dns.com.\t1\tIN\tA\t162.125.64.3<\/pre>\n<p>U z\u00e1znamu <code>safebrowsing.googleapis.com<\/code> je TTL 60 sekund, jako u dom\u00e9n Facebooku. A z pohledu klienta se tyto hodnoty zmen\u0161uj\u00ed na polovinu.<\/p>\n<h1>Jak je to s nastaven\u00edm minim\u00e1ln\u00edho TTL?<\/h1>\n<p>S pou\u017eit\u00edm n\u00e1zvu, typu dotazu, TTL a p\u016fvodn\u011b ulo\u017een\u00e9ho \u010dasov\u00e9ho raz\u00edtka jsem napsal skript pro simulaci 1,5 milionu dotaz\u016f proch\u00e1zej\u00edc\u00edch ke\u0161ovac\u00edm resolverem za \u00fa\u010delem vyhodnocen\u00ed objemu zbyte\u010dn\u00fdch dotaz\u016f odeslan\u00fdch kv\u016fli vypr\u0161en\u00ed platnosti existuj\u00edc\u00edho z\u00e1znamu v ke\u0161i.<\/p>\n<p>47,4 % dotaz\u016f bylo provedeno po vypr\u0161en\u00ed platnosti existuj\u00edc\u00edho z\u00e1znamu. To je neod\u016fvodn\u011bn\u011b vysok\u00e9.<\/p>\n<p>Jak\u00fd vliv bude m\u00edt nastaven\u00ed minim\u00e1ln\u00edho TTL na ke\u0161ov\u00e1n\u00ed?<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/3abd417d312450519b45f66865b23763.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Osa X jsou minim\u00e1ln\u00ed hodnoty TTL. Z\u00e1znamy s p\u016fvodn\u00edmi TTL nad tuto hodnotu nejsou ovlivn\u011bny.<\/p>\n<p>Osa Y je procento po\u017eadavk\u016f od klienta, kter\u00fd ji\u017e m\u00e1 ulo\u017een\u00fd z\u00e1znam v cache, ale jeho platnost vypr\u0161ela a prov\u00e1d\u00ed nov\u00fd po\u017eadavek.<\/p>\n<p>Pod\u00edl \"nadbyte\u010dn\u00fdch\" po\u017eadavk\u016f se sni\u017euje z 47 % na 36 % jednoduch\u00fdm nastaven\u00edm minim\u00e1ln\u00edho TTL na 5 minut. P\u0159i nastaven\u00ed minim\u00e1ln\u00edho TTL na 15 minut kles\u00e1 po\u010det t\u011bchto po\u017eadavk\u016f na 29 %. Minim\u00e1ln\u00ed TTL na 1 hodinu sni\u017euje jejich po\u010det na 17 %. V\u00fdznamn\u00fd rozd\u00edl!<\/p>\n<p>Co kdybychom na stran\u011b serveru nic nezm\u011bnili, ale m\u00edsto toho nastavili minim\u00e1ln\u00ed TTL v klientsk\u00fdch DNS cache (routery, m\u00edstn\u00ed resolver)?<\/p>\n<p><img decoding=\"async\" alt=\"P\u0159esta\u0148te pou\u017e\u00edvat sm\u011b\u0161n\u011b n\u00edzk\u00e9 TTL pro DNS\" src=\"\/wp-content\/uploads\/2019\/11\/107a2bd53797d421d65ac7260bf78dfe.jpg\" style=\"display:block;margin: 0 auto;\"><\/p>\n<p>Po\u010det po\u017eadovan\u00fdch po\u017eadavk\u016f kles\u00e1 z 47 % na 34 % p\u0159i nastaven\u00ed minim\u00e1ln\u00edho TTL na 5 minut, na 25 % p\u0159i minim\u00e1ln\u011b 15 minut\u00e1ch a na 13 % p\u0159i minim\u00e1ln\u011b 1 hodin\u011b. Mo\u017en\u00e1 je optim\u00e1ln\u00ed hodnota 40 minut.<\/p>\n<p>Dopad t\u00e9to minim\u00e1ln\u00ed zm\u011bny je obrovsk\u00fd.<\/p>\n<h1>Jak\u00e9 jsou d\u016fsledky?<\/h1>\n<p>Samoz\u0159ejm\u011b, slu\u017ebu lze p\u0159ev\u00e9st k nov\u00e9mu cloudov\u00e9mu poskytovateli, na nov\u00fd server, do nov\u00e9 s\u00edt\u011b, co\u017e vy\u017eaduje, aby klienti pou\u017e\u00edvali posledn\u00ed DNS z\u00e1znamy. A dostate\u010dn\u011b n\u00edzk\u00fd TTL pom\u00e1h\u00e1 realizovat tento p\u0159echod hladce a nen\u00e1padn\u011b. Ale p\u0159i p\u0159echodu na novou infrastrukturu nikdo neo\u010dek\u00e1v\u00e1, \u017ee klienti p\u0159ejdou na nov\u00e9 DNS z\u00e1znamy b\u011bhem 1 minuty, 5 minut nebo 15 minut. Nastaven\u00ed minim\u00e1ln\u00ed doby \u017eivotnosti na 40 minut m\u00edsto 5 minut nebr\u00e1n\u00ed u\u017eivatel\u016fm v p\u0159\u00edstupu k slu\u017eb\u011b.<\/p>\n<p>To v\u0161ak v\u00fdrazn\u011b sn\u00ed\u017e\u00ed zpo\u017ed\u011bn\u00ed a zv\u00fd\u0161\u00ed soukrom\u00ed a spolehlivost, co\u017e p\u0159edejde zbyte\u010dn\u00fdm po\u017eadavk\u016fm.<\/p>\n<p>Samoz\u0159ejm\u011b, RFC \u0159\u00edk\u00e1, \u017ee je t\u0159eba striktn\u011b dodr\u017eovat TTL. Ale realita je takov\u00e1, \u017ee syst\u00e9m DNS se stal p\u0159\u00edli\u0161 neefektivn\u00edm.<\/p>\n<p>Pokud pracujete s autoritativn\u00edmi DNS servery, pros\u00edm zkontrolujte sv\u00e9 TTL. Opravu pot\u0159ebujete tak sm\u011b\u0161n\u011b n\u00edzk\u00e9 hodnoty?<\/p>\n<p>Samoz\u0159ejm\u011b, existuj\u00ed p\u00e1dn\u00e9 d\u016fvody pro nastaven\u00ed n\u00edzk\u00fdch TTL pro DNS z\u00e1znamy. Ale ne pro 75 % DNS provozu, kter\u00fd se prakticky nem\u011bn\u00ed.<\/p>\n<p>A pokud z n\u011bjak\u00fdch d\u016fvod\u016f opravdu pot\u0159ebujete pou\u017e\u00edvat n\u00edzk\u00e9 TTL pro DNS, z\u00e1rove\u0148 se ujist\u011bte, \u017ee na va\u0161em webu nen\u00ed zapnuto cachov\u00e1n\u00ed. Z t\u00fdch\u017e d\u016fvod\u016f.<\/p>\n<p>Pokud m\u00e1te spu\u0161t\u011bnou m\u00edstn\u00ed DNS cache, jako je <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/dnscrypt\/dnscrypt-proxy\">dnscrypt-proxy<\/a><\/noindex>, kter\u00fd umo\u017e\u0148uje nastavovat minim\u00e1ln\u00ed TTL, vyu\u017eijte tuto funkci. Je to v po\u0159\u00e1dku. Nic \u0161patn\u00e9ho se nestane. Nastavte minim\u00e1ln\u00ed TTL p\u0159ibli\u017en\u011b mezi 40 minutami (2400 sekund) a 1 hodinou. Naprosto rozumn\u00fd rozsah.<\/p>\n<p>Zdroj: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/post\/474450\/\">habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u041d\u0438\u0437\u043a\u0430\u044f \u0437\u0430\u0434\u0435\u0440\u0436\u043a\u0430 DNS \u2014 \u043a\u043b\u044e\u0447\u0435\u0432\u043e\u0439 \u0444\u0430\u043a\u0442\u043e\u0440 \u0434\u043b\u044f \u0431\u044b\u0441\u0442\u0440\u043e\u0439 \u0440\u0430\u0431\u043e\u0442\u044b \u0432 \u0438\u043d\u0442\u0435\u0440\u043d\u0435\u0442\u0435. \u0427\u0442\u043e\u0431\u044b \u0435\u0451 \u043c\u0438\u043d\u0438\u043c\u0438\u0437\u0438\u0440\u043e\u0432\u0430\u0442\u044c, \u0432\u0430\u0436\u043d\u043e \u0442\u0449\u0430\u0442\u0435\u043b\u044c\u043d\u043e \u043f\u043e\u0434\u043e\u0431\u0440\u0430\u0442\u044c DNS-\u0441\u0435\u0440\u0432\u0435\u0440\u044b \u0438 \u0430\u043d\u043e\u043d\u0438\u043c\u043d\u044b\u0435 \u0440\u0438\u043b\u0435\u0438. \u041d\u043e \u043f\u0435\u0440\u0432\u044b\u043c \u0434\u0435\u043b\u043e\u043c \u0441\u043b\u0435\u0434\u0443\u0435\u0442 \u0438\u0437\u0431\u0430\u0432\u0438\u0442\u044c\u0441\u044f \u043e\u0442 \u0431\u0435\u0441\u043f\u043e\u043b\u0435\u0437\u043d\u044b\u0445 \u0437\u0430\u043f\u0440\u043e\u0441\u043e\u0432. \u0418\u043c\u0435\u043d\u043d\u043e \u043f\u043e\u044d\u0442\u043e\u043c\u0443 DNS \u0438\u0437\u043d\u0430\u0447\u0430\u043b\u044c\u043d\u043e \u0441\u043e\u0437\u0434\u0430\u0432\u0430\u043b\u0441\u044f \u043a\u0430\u043a \u0441\u0438\u043b\u044c\u043d\u043e \u043a\u044d\u0448\u0438\u0440\u0443\u0435\u043c\u044b\u0439 \u043f\u0440\u043e\u0442\u043e\u043a\u043e\u043b. \u0410\u0434\u043c\u0438\u043d\u0438\u0441\u0442\u0440\u0430\u0442\u043e\u0440\u044b \u0437\u043e\u043d \u0443\u0441\u0442\u0430\u043d\u0430\u0432\u043b\u0438\u0432\u0430\u044e\u0442 \u0432\u0440\u0435\u043c\u044f \u0436\u0438\u0437\u043d\u0438 (TTL) \u0434\u043b\u044f \u043e\u0442\u0434\u0435\u043b\u044c\u043d\u044b\u0445 \u0437\u0430\u043f\u0438\u0441\u0435\u0439, \u0430 \u0440\u0435\u0437\u043e\u043b\u0432\u0435\u0440\u044b \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u0443\u044e\u0442 \u044d\u0442\u0443 \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0446\u0438\u044e \u043f\u0440\u0438 \u0445\u0440\u0430\u043d\u0435\u043d\u0438\u0438 \u0437\u0430\u043f\u0438\u0441\u0435\u0439 [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-52324","post","type-post","status-publish","format-standard","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.3 - aioseo.com -->\n\t<meta name=\"description\" content=\"\u041d\u0438\u0437\u043a\u0430\u044f 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