General
- You must be able to draw a diagram covering the web stack you built with the sysadmin/devops track projects
- You must be able to explain what each component is doing
- You must be able to explain system redundancy
- Know all the mentioned acronyms: LAMP, SPOF, QPS
- The DNS, or Domain Name System, acts like a giant phonebook for the internet. It translates human-readable domain names (like "[invalid URL removed]") into numerical IP addresses (like 172.217.160.132) that computers use to connect to each other. Here's a breakdown of how it works:
- Whenever u browse a specific website (google.com), the browser have to get it's IP address in order to browse it, so first the browser searches for the IP in it's cache, if not found then will search in the OS cache, if not found the DNS is starting to do it's role (
- The OS will ask the resolver to got the IP of google.com, then the resolver will search in it's cache, if it's not found then the resolver will make a short trip to got it.
- Resolver will ask the Root Server for it, but the Root Server will response with the Top Level Domain Server (TLD Server) [.com TLD Server, .org TLD Server ...] then TLD will response with the Authoritative name servers addresses, then the authoritative will reply with the IP address of google.com.
- )
- This interesting journey explained here: https://howdns.works/ep1/
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A Record:
- Stands for Address record, It maps the domain name to IPv4 address.
- Use dig command line to find A record for a specific website (dig A www.dnsimple.com).
- https://support.dnsimple.com/articles/a-record/
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AAAA Record:
- Same as A Record but for IPv6.
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CNAME Record:
- Stands for Canonical Name, and it always points to another domain name, never points to IP.
- An A record for example.com pointing to the server IP address
- A CNAME record for www.example.com pointing to example.com
- Use dig command line to find A record for a specific website (dig CNAM www.dnsimple.com).
- https://support.dnsimple.com/articles/cname-record/
- Stands for Canonical Name, and it always points to another domain name, never points to IP.
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MX Record:
- Stands for Mail Exchange.
- For more details: https://support.dnsimple.com/articles/mx-record/
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TXT Record:
- It distribute the requests to multiple or several systems or servers.
- Load balancers like (HAProxy, Nginx, ...) are using some algos to acheive it:
- Weighted Scheduling Algo.
- Round Robin Scheduling Algo.
- Least Connection First Scheduling Algo.
- For more details: https://www.thegeekstuff.com/2016/01/load-balancer-intro/