Low DNS latency ndiye chinsinsi chakusakatula mwachangu pa intaneti. Kuti muchepetse, ndikofunikira kusankha mosamala ma seva a DNS ndi . Koma choyamba ndikuchotsa mafunso opanda pake.
Ichi ndichifukwa chake DNS idapangidwa kuti ikhale protocol yosungika kwambiri. Oyang'anira Zone amakhazikitsa nthawi yokhalamo (TTL) pazolemba pawokha, ndipo otsimikiza amagwiritsa ntchito chidziwitsochi posunga zolembera kuti apewe magalimoto osafunikira.
Kodi caching ndi yothandiza? Zaka zingapo zapitazo, kafukufuku wanga wochepa adawonetsa kuti sizinali zangwiro. Tiyeni tione mmene zinthu zilili panopa.
Kuti nditole zambiri ndalemba zigamba kuti musunge mtengo wa TTL poyankha. Imatanthauzidwa ngati TTL yochepa ya zolemba zake pa pempho lililonse lomwe likubwera. Izi zimapereka chithunzithunzi chabwino cha kugawa kwa TTL kwa magalimoto enieni, komanso kumaganiziranso kutchuka kwa zopempha za munthu aliyense. Mtundu wokhazikika wa seva unagwira ntchito kwa maola angapo.
Zotsatira zake zimakhala ndi zolemba 1 (dzina, qtype, TTL, timestamp). Nayi kugawa kwathunthu kwa TTL (X-axis ndi TTL mumasekondi):
Kupatula kugunda kwapang'ono ku 86 (makamaka ma rekodi a SOA), zikuwonekeratu kuti ma TTL ali otsika. Tiyeni tiwone bwinobwino:
Chabwino, ma TTL opitilira ola limodzi sizofunikira. Kenako tiyeni tiyang'ane pamtundu wa 1β0:
Ma TTL ambiri amachokera ku 0 mpaka 15 mphindi:
Zambiri ndi kuyambira mphindi 0 mpaka 5:
Si zabwino kwambiri.
Kugawidwa kowonjezereka kumapangitsa kuti vutoli liwonekere kwambiri:
Theka la mayankho a DNS ali ndi TTL ya mphindi imodzi kapena kuchepera, ndipo magawo atatu mwa magawo atatu aliwonse ali ndi TTL ya mphindi 1 kapena kuchepera.
Koma dikirani, ndizoipa kwambiri. Kupatula apo, iyi ndi TTL yochokera ku maseva ovomerezeka. Komabe, okonza kasitomala (mwachitsanzo, ma routers, ma cache am'deralo) amalandira TTL kuchokera kumtunda, ndipo imachepera sekondi iliyonse.
Chifukwa chake kasitomala amatha kugwiritsa ntchito cholowa chilichonse, pafupifupi, theka la TTL yoyambirira asanatumize pempho latsopano.
Mwina ma TTL otsika kwambiriwa amagwira ntchito pazopempha zachilendo osati mawebusayiti odziwika ndi ma API? Tiyeni tiwone:
X axis ndi TTL, Y axis ndi kutchuka kwamafunso.
Tsoka ilo, mafunso odziwika kwambiri ndiwonso oyipa kwambiri kusungitsa.
Tiyeni tiwone pafupi:
Chigamulo: ndizoipa kwambiri. Zinali zoipa kale, koma zinafika poipa. DNS caching yakhala yopanda phindu. Pamene anthu ochepa amagwiritsa ntchito ISP's DNS solver (pazifukwa zabwino), kuwonjezeka kwa latency kumawonekera kwambiri.
DNS caching yakhala yothandiza pazinthu zomwe palibe amene amayendera.
Chonde dziwani kuti pulogalamuyo ikhoza kutanthauzira ma TTL otsika.
Chifukwa chiyani
Chifukwa chiyani zolemba za DNS zimayikidwa ku TTL yotsika chonchi?
- Zoyeserera zolemetsa zolowa zidasiyidwa ndi zosintha zosasintha.
- Pali nthano zoti DNS load balancing imadalira TTL (izi sizowona - kuyambira masiku a Netscape Navigator, makasitomala asankha adilesi ya IP mwachisawawa kuchokera pagulu la ma RRs ndikuyesanso ina ngati sangathe kulumikizana)
- Oyang'anira akufuna kuyika zosintha nthawi yomweyo, kotero ndikosavuta kukonzekera.
- Woyang'anira seva ya DNS kapena woyezera katundu amawona ntchito yake ngati kugwiritsa ntchito bwino makonzedwe omwe ogwiritsa ntchito amapempha, osati kufulumizitsa masamba ndi ntchito.
- Ma TTL otsika amakupatsani mtendere wamalingaliro.
- Anthu poyamba ankaika ma TTL otsika kuti ayezedwe ndikuiwala kusintha.
Sindinaphatikizepo "olephera" pamndandandawo chifukwa akuyamba kucheperachepera. Ngati mukufuna kutumizira ogwiritsa ntchito ku netiweki ina kuti mungowonetsa tsamba lolakwika pomwe china chilichonse chasweka, kuchedwa kopitilira mphindi imodzi ndikovomerezeka.
Kuphatikiza apo, TTL yamphindi imodzi imatanthawuza kuti ngati ma seva ovomerezeka a DNS atsekedwa kwa mphindi yopitilira 1, palibe wina aliyense amene azitha kupeza ntchito zodalira. Ndipo redundancy sizingathandize ngati chifukwa chake ndi cholakwika kasinthidwe kapena kuthyolako. Kumbali ina, ndi ma TTL oyenera, makasitomala ambiri apitiliza kugwiritsa ntchito kasinthidwe koyambirira ndipo samazindikira chilichonse.
Ntchito za CDN ndi zolemetsa zolemetsa ndizo makamaka zomwe zimachititsa ma TTL otsika, makamaka akaphatikiza ma CNAME okhala ndi ma TTL otsika ndi marekodi okhala ndi ma TTL otsika (koma odziyimira pawokha):
$ drill raw.githubusercontent.com raw.githubusercontent.com. 9 IN CNAME github.map.fastly.net. github.map.fastly.net. 20 IN A 151.101.128.133 github.map.fastly.net. 20 IN A 151.101.192.133 github.map.fastly.net. 20 IN A 151.101.0.133 github.map.fastly.net. 20 IN A 151.101.64.133
Nthawi zonse CNAME kapena zolemba zilizonse za A zikatha ntchito, pempho latsopano liyenera kutumizidwa. Onsewa ali ndi TTL yachiwiri ya 30, koma sizofanana. Pafupifupi pafupifupi TTL idzakhala masekondi 15.
Koma dikirani! Ndizovuta kwambiri. Ena okonza zinthu amachita moyipa kwambiri pamenepa ndi ma TTL awiri otsika:
$ drill raw.githubusercontent.com @4.2.2.2 raw.githubusercontent.com. 1 MU CNAME github.map.fastly.net. github.map.fastly.net. 1 MU A 151.101.16.133
Level3 solver mwina imayenda pa BIND. Mukapitiriza kutumiza pempholi, TTL ya 1 idzabwezedwa nthawi zonse. raw.githubusercontent.com sichinasungidwe konse.
Nachi chitsanzo china chazimenezi ndi malo otchuka kwambiri:
$ drill detectportal.firefox.com @1.1.1.1 detectportal.firefox.com. 25 IN CNAME detectportal.prod.mozaws.net. detectportal.prod.mozaws.net. 26 IN CNAME detectportal.firefox.com-v2.edgesuite.net. detectportal.firefox.com-v2.edgesuite.net. 10668 IN CNAME a1089.dscd.akamai.net. a1089.dscd.akamai.net. 10 IN A 104.123.50.106 a1089.dscd.akamai.net. 10 IN A 104.123.50.88
Zolemba zosachepera zitatu za CNAME. Ayi. Wina ali ndi TTL yabwino, koma ndiyopanda phindu. Ma CNAME ena ali ndi TTL yoyamba ya masekondi 60, koma madambwe akamai.net pazipita TTL ndi 20 masekondi ndipo palibe amene ali mu gawo.
Nanga bwanji madambwe omwe amafufuza zida za Apple nthawi zonse?
$ drill 1-courier.push.apple.com @4.2.2.2 1-courier.push.apple.com. 1253 IN CNAME 1.courier-push-apple.com.akadns.net. 1.courier-push-apple.com.akadns.net. 1 IN CNAME gb-courier-4.push-apple.com.akadns.net. gb-courier-4.push-apple.com.akadns.net. 1 IN A 17.57.146.84 gb-courier-4.push-apple.com.akadns.net. 1 IN A 17.57.146.85
Vuto lomwelo monga Firefox ndi TTL zidzakhazikika pamphindi imodzi nthawi zambiri mukamagwiritsa ntchito Level1 resolution.
Dropbox?
$ drill client.dropbox.com @8.8.8.8 client.dropbox.com. 7 MU CNAME client.dropbox-dns.com. client.dropbox-dns.com. 59 MU A 162.125.67.3 $ drill client.dropbox.com @4.2.2.2 client.dropbox.com. 1 MU CNAME client.dropbox-dns.com. client.dropbox-dns.com. 1 MU A 162.125.64.3
Pa kujambula safebrowsing.googleapis.com Mtengo wa TTL ndi masekondi 60, ngati madera a Facebook. Ndipo, kachiwiri, kuchokera kumalingaliro a kasitomala, zikhalidwe izi zimachepetsedwa.
Nanga bwanji kukhazikitsa TTL yocheperako?
Pogwiritsa ntchito dzina, mtundu wa pempho, TTL, ndi sitempu yosungidwa yoyambirira, ndidalemba script kuti ndifanane ndi zopempha 1,5 miliyoni zomwe zimadutsa pa caching resolution kuti ndiyerekeze kuchuluka kwa zopempha zosafunikira zomwe zidatumizidwa chifukwa cholemba kale.
47,4% ya zopempha zidapangidwa pambuyo poti mbiri yomwe ilipo itatha. Izi ndizokwera mopanda chifukwa.
Zingakhale bwanji pa caching ngati TTL yocheperako yakhazikitsidwa?
X axis ndiye ma TTL ochepa. Zolemba zokhala ndi magwero a TTL pamwamba pa mtengowu sizikhudzidwa.
The Y axis ndi kuchuluka kwa zopempha kuchokera kwa kasitomala yemwe ali kale ndi malo osungidwa, koma zatha ndipo akupanga pempho latsopano.
Gawo la zopempha "zowonjezera" lachepetsedwa kuchoka pa 47% kufika pa 36% mwa kungoyika TTL yocheperako mpaka mphindi zisanu. Pokhazikitsa TTL yocheperako mpaka mphindi 5, kuchuluka kwa zopemphazi kumatsika mpaka 15%. TTL yochepa ya ola limodzi imawachepetsa mpaka 29%. Kusiyana kwakukulu!
Nanga bwanji osasintha chilichonse kumbali ya seva, koma m'malo mwake kuyika TTL yocheperako mumakasitomala a DNS cache (marouter, osinthira am'deralo)?
Chiwerengero cha zopempha zofunika chikutsika kuchokera 47% mpaka 34% ndi TTL osachepera mphindi 5, 25% ndi osachepera mphindi 15, ndi 13% ndi osachepera 1 ora. Mwina mphindi 40 ndizoyenera.
Zotsatira za kusintha kwakung'ono kumeneku ndi kwakukulu.
Zotsatira zake ndi zotani?
Zoonadi, ntchitoyi ingasunthidwe kwa wopereka mtambo watsopano, seva yatsopano, intaneti yatsopano, yomwe imafuna kuti makasitomala agwiritse ntchito zolemba za DNS zatsopano. Ndipo TTL yaying'ono imathandizira kuti izi zitheke bwino komanso mosazindikira. Koma ndikusintha kwa zomangamanga zatsopano, palibe amene amayembekeza kuti makasitomala asamukire ku zolemba zatsopano za DNS mkati mwa mphindi imodzi, mphindi 1, kapena mphindi 5. Kuyika TTL yocheperako kukhala mphindi 15 m'malo mwa mphindi 40 sikungalepheretse ogwiritsa ntchito kupeza ntchito.
Komabe, izi zidzachepetsa kwambiri latency ndikuwongolera zinsinsi ndi kudalirika popewa zopempha zosafunikira.
Zachidziwikire, ma RFC amati TTL iyenera kutsatiridwa mosamalitsa. Koma zoona zake nβzakuti dongosolo la DNS lakhala losakwanira.
Ngati mukugwira ntchito ndi ma seva ovomerezeka a DNS, chonde onani ma TTL anu. Kodi mumafunikiradi makhalidwe otsika mochititsa manyazi chonchi?
Zachidziwikire, pali zifukwa zomveka zokhazikitsira ma TTL ang'onoang'ono a zolemba za DNS. Koma osati 75% ya magalimoto a DNS omwe amakhala osasinthika.
Ndipo ngati pazifukwa zina muyenera kugwiritsa ntchito ma TTL otsika a DNS, nthawi yomweyo onetsetsani kuti tsamba lanu lilibe caching. Pazifukwa zomwezo.
Ngati muli ndi cache ya DNS yapafupi, monga zomwe zimakupatsani mwayi woyika ma TTL ochepa, gwiritsani ntchito ntchitoyi. Izi nzabwino. Palibe choipa chimene chidzachitike. Khazikitsani TTL yocheperako kukhala pafupifupi mphindi 40 (masekondi 2400) ndi ola limodzi. Kusiyanasiyana koyenera.
Source: www.habr.com