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session-08.txt
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How DNS works?
--------------------
DNS is like a dictionary...
key=value
daws78s.online=IP address
when you enter joindevops.com first time? what happens here?
Where can I find IP address?
browser checks its cache?
if not find anything? then it asks OS
OS checks it's cache. If not finds anything
OS sends a request to ISP.... it is ISP responsibility to get the IP address of a domain
DNS resolution...
Resolver is the component responsible to fetch IP address. it is from ISP.
All ISP are configured with how to send a request to root servers..
Root servers
------------------------
Oxford is the base for English dictionary...
Who owns root servers? --> ICANN Internet corporation for assigned names and numbers
----------------------
12 non profit organisations across the world manages these root servers...
13 root servers across the world with many servers in background..
I want IP address for joindevops.com
Root servers
TLD
.com .net .org .in .us .uk .online .ai .shop .site .edu .org .co .inc
Root server will give the information of .com TLD...
this info will be stored in resolver cache...
it will contact .com TLD....
.com TLD should maintain what is the IP address of joindevops.com
Domain Registars/Providers
---------------------------
godaddy hostinger route53 google
when you buy a domain in hostinger, they will update .com TLD about your domain, address details, etc.
domain name
address
nameservers
hostinger --> AWS transfer
I updated AWS NS in hostinger...
hostinger will update nameservers to the TLD. Now .online TLD have AWS nameserver details
daws78s.online --> resolver contacts .online TLD
.online TLD will give nameserver details....
resolver will get AWS NS details...
then resolver will contact AWS NS. Then AWS will give A record
.siva
fastest automated way
---------------------
without touching the configurations and servers
if you do any config change, you have to restart application...
A record --> IP address of the domain
NS --> authoritive nameservers
SOA --> Ownership record
CNAME(canonical name) --> another domain
MX records --> mail servers
[email protected] --> MX records
soft link vs hardlink
-----------------------
what is inode?
inode stores the file metadata actually.
inode = indexnode
14950849
storage location, ownership, permissions, etc.
shortcut --> points to the real location
hard link --> another copy
if I delete main file, can soft link work? no it will not work
if I delete main file , can hard link work? Yes it will work
softlink/symlink is the short cut to the file, if you remove actually symlink will not work...
hardlink is another copy of file, if you remove main file, hard link will work?
does inode of softlink is same as main file? inode is same
inode is different
does inode of hardlink is same as main file? yes inode is same
when someone deletes the main file, do you think file storage is deleted?
NO.. because other hard links are pointing to this
ln == link
Linux Folder Structure
----------------------
/root --> directory for root user
/bin --> binaries, while system is starting these binaries will load
/boot --> When linux system starts, Linux starts boot loading from here
/dev = devices --> hard disk, keyboard, devcices
/etc = extra configuration = /etc/nginx
/home = Linux stores all users in home location
/lib = operating system libraries
/media = cd or dvd drives
/mnt = you can mount other disks
/opt = optional = if you are installing any package manually, prefer opt location
/proc = pid info and processor info
/sbin = admin commands
/tmp = it is temp, not an important
/usr = user commmands, libraries, documents
/var = variables.. mainly log files