Shadowing Practice: Everything You Need to Know About DNS: Crash Course System Design #4 - Learn English Speaking with Video
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DNS or domain name system is the backbone of the internet,
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but few know exactly how it works.
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In this video, we'll learn all about the system design of DNS.
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Let's dive right in.
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DNS is the internet's directory.
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It translates human readable domain names such as google.com to machine readable IP addresses.
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DNS is a little confusing because there are different types of DNS server in the DNS hierarchy,
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each serving a different purpose.
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When a browser makes a DNS query,
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it's asking a DNS resolver.
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Now this DNS resolver could be from our ISP or from popular DNS providers like Cloudflare's 1.1.1.1 or Google's 8.8.8.8.
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If the DNS resolver does not have the answer in its cache,
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it finds the right authoritative nameserver and asks it.
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The authoritative nameserver is the one that holds the answer.
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When we update a domain's DNS records as a site owner,
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we are updating its authoritative nameserver.
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How does the DNS resolver find the authoritative nameserver?
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This is where the system of DNS gets interesting.
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There are three main levels of authoritative DNS servers.
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There are the root name servers,
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the top level domain or TLD name servers,
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and the authoritative name servers for the domains.
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The root name servers store the IP addresses of the TLD name servers.
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There are 13 logical root name servers.
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Each root name server has a single IP address assigned to it.
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There are actually many physical servers behind each IP address.
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Through the magic of Anycast,
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we get routed to the one closest to us.
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The TLD name servers store the IP addresses of the authoritative name servers for all the domains under them.
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There are many types of TLD names.
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We are all familiar with .com, .org, and .edu.
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There are also country code TLDs like .de and .uk.
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There are many others.
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The authoritative nameservers for a domain provide well,
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authoritative answers to DNS queries.
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When we register a domain,
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the registrar hosts the authoritative nameservers by default,
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but we can change them to others.
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Cloud providers like AWS and Cloudflare run robust authoritative nameservers.
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This hierarchical design makes DNS highly decentralized and robust.
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Now let's walk through the life of a typical DNS query.
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The user types google.com into the browser.
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The browser first checks its cache.
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If it has no answer,
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it makes an operating system call to try to get the answer.
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The operating system call would most likely have its own cache too.
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If the answer isn't there,
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it reaches out to the DNS resolver.
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The DNS resolver first checks its cache.
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If it is not there or if the answer has expired,
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it asks the root name server.
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The root name server responds with the list of the .com TLD name servers.
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Note that since .com is such a common TLD,
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the resolver most likely already caches the IP addresses for those .com TLD name servers.
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The DNS resolver then reaches out to the .com TLD name server and the .com TLD name server
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returns the authoritative name servers for google.com.
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And finally, the DNS resolver reaches out to google.com's authoritative name server,
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and it returns the IP addresses of google.com.
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Now the DNS resolver then returns the IP addresses to the operating system,
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and the operating system returns them to the browser.
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Finally, let's go over some gotchas when updating DNS records for a live high traffic production system.
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DNS propagation is slow because there is a TTL on each DNS record.
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And some of the default TTLs are pretty long.
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Also, not every DNS resolver is a good citizen.
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There are some buggy ones out there that don't honor the TTL.
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To mitigate the risk, there are two practical steps to take.
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First, reduce the TTL for the record that we want to change to something very short,
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say 60 seconds, well in advance before the update actually happens.
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This gives ample time for all the DNS servers to receive the shortened TTL,
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which would allow the actual record update to take effect based on the new shortened TTL.
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Second, leave the server running on the old IP addresses for a while.
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Only decommission the server when traffic dies down to an acceptable level.
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Because some DNS resolvers don't honor the TTL,
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this could take a bit of time and patience.
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This concludes our video on DNS.
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We hope you have a better understanding of how its hierarchical design makes it decentralized and robust.
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Remember, DNS is what translates domain names to IP addresses,
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making it a critical component of the Internet backbone.
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You like our videos, you may like our system design newsletter as well.
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It covers topics and trends in large-scale system design.
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Vocabulario y notas de pronunciación para esta lección
Esta lección de conversación de nivel C1 se basa en el vídeo “Everything You Need to Know About DNS: Crash Course System Design”. Las palabras que más se repiten: Dns, server, authoritative, resolver, Tld. Este vídeo tiene 81 frases y 794 palabras para practicar shadowing. La parte hablada dura 5:29. El hablante mantiene un ritmo constante de unas 145 palabras por minuto, cómodo para el shadowing. Solo el 69 % de las palabras está entre las 3.000 más comunes del inglés, por lo que el vocabulario es exigente.
Vocabulario clave de este vídeo
Las 15 palabras más avanzadas del vídeo, con su pronunciación y significado:
| Palabra | Pronunciación | Significado |
|---|---|---|
| authoritative adjetivo | /əˈθɔɹɪˌteɪtɪv/ | autoritativo, oficial |
| cache sustantivo | /kæʃ/ | memoria caché, caché |
| query sustantivo | /ˈkwɪɹ.i/ | consulta, pregunta |
| robust adjetivo | /ɹəʊˈbʌst/ | robusto |
| decentralize verbo | /diːˈsɛntɹəlaɪz/ | descentralizar |
| hierarchical adjetivo | /ˌhaɪəˈɹɑːkɪkəl/ | jerárquico |
| readable adjetivo | /ˈɹiː.də.bəl/ | ameno |
| shorten verbo | /ˈʃɔɹtn̩/ | acortar, acorzar |
| backbone sustantivo | /ˈbækˌboʊn/ | espina dorsal, columna vertebral |
| translate verbo | /tɹænzˈleɪt/ | traducir, trasladar |
| decommission verbo | /diːkəˈmɪʃən/ | desmantelar, dar de baja |
| gotcha | /ˈɡɑ.tʃə/ | te tengo, te atrapé |
| propagation sustantivo | /pɹɑpəˈɡeɪʃən/ | propagación |
| registrar sustantivo | /ˈɹɛd͡ʒ.ɪsˌtɹɑɹ/ | registrador |
| mitigate verbo | /ˈmɪt.ɪ.ɡeɪt/ | mitigar |
Phrasal verbs que vas a escuchar
| Palabra | Significado |
|---|---|
| go over verbo | sentar, pasar |
| walk through verbo | explicar paso a paso, enseñar |
Pronunciación a tener en cuenta
El hablante usa 4 contracciones y formas reducidas, como don't, isn't, we'll. Dilas en su forma corta, tal como las oyes.
- Los sonidos de “sh” y “zh”: cache /kæʃ/, shorten /ˈʃɔɹtn̩/, decommission /diːkəˈmɪʃən/, propagation /pɹɑpəˈɡeɪʃən/
- Palabras largas — cuida el acento: authoritative /əˈθɔɹɪˌteɪtɪv/, decentralize /diːˈsɛntɹəlaɪz/, hierarchical /ˌhaɪəˈɹɑːkɪkəl/, decommission /diːkəˈmɪʃən/, propagation /pɹɑpəˈɡeɪʃən/
Sonidos difíciles para hispanohablantes:
- /z/ — sonora, no /s/: browser /ˈbɹaʊ.zəɹ/, decentralize /diːˈsɛntɹəlaɪz/, translate /tɹænzˈleɪt/, confuse /kənˈfjuːz/, newsletter /ˈn(j)uzˌlɛtɚ/
- /h/ — una aspiración suave, no la “j”: hierarchical /ˌhaɪəˈɹɑːkɪkəl/, hierarchy /ˈhaɪ.ə.ɹɑː(ɹ).ki/
Cómo practicar con este vídeo
- Escucha el vídeo entero una vez sin hablar y anota las palabras que no conoces.
- Haz shadowing frase por frase a velocidad normal, repitiendo cada una hasta que tu ritmo coincida con el del hablante.
- Grábate y compara con el original, prestando atención a palabras como authoritative, cache, query.
¿Qué es la Técnica de Shadowing?
Shadowing es una técnica de aprendizaje de idiomas respaldada por la ciencia, desarrollada originalmente para la formación de intérpretes profesionales y popularizada por el políglota Dr. Alexander Arguelles. El método es simple pero poderoso: escuchas audio en inglés nativo y lo repites en voz alta de inmediato, como una sombra que sigue al hablante con solo 1-2 segundos de retraso. A diferencia de la escucha pasiva o los ejercicios de gramática, el shadowing obliga a tu cerebro y músculos de la boca a procesar y reproducir simultáneamente patrones de habla reales. Las investigaciones muestran que mejora significativamente la precisión de la pronunciación, la entonación, el ritmo, el habla conectada, la comprensión auditiva y la fluidez al hablar, convirtiéndola en una de las metodologías más efectivas para la preparación del IELTS Speaking y la comunicación en inglés en el mundo real.