Cloud Classroom Series – 25/Jul/2020

TCP/OSI Model

  • This model uses layers to help give a visual description of what is going on with a particular networking system
  • OSI Model Preview
  • Each Layer has funcationalities
    • Layer 1: Physical: This layer defines the logic levels, data rate, physical media & data conversion functions
    • Layer 2: Data link: Package & Unpackage the data in frames
    • Layer 3: Network: This network layer handles packet routing and switching
    • Layer 4: transport: This layer provides the quality of service functions. TCP is part
    • Layer 5: Session: This layer handles authentications & authorization
    • Layer 6: Presentation Layer: This layer checks the data & it can handle encryptions & decryptions
    • Layer 7: This layer used communication protocols like http, IMAP, SMTP.
  • When we speak of cloud we use tcp/http(s), So we need to worry about Layer 4 & layer 7
  • Transport Layer Protocols
    • TCP
    • UDP
  • Port is defined at the Transport Layer (Layer 4)

Multiple Servers to Handle Load

  • As the load increase on web/application servers we can solve the issue

    • By increasing RAM/CPU (Vertical Scaling)
    • By increasing servers and sharing load b/w them (Horizontal scaling)
  • Most of the organizations prefer Horizontal scaling especially in cloud

  • Since the multiple servers are involved, we would add a load balancer and use that as an interface to our multiple servers Preview

  • There are two types of load balancers

    • Software Load balancers
    • Hardware Load balancers
  • Load balancer whenever a client sends a traffic to which server should i forward? Preview

  • To solve this load balancers have load balancing algorithms

    • Round-Robin: Requests are evenly distributed across servers sequentially
    • Least Connections: A new request is sent to the server which has fewest connections at that moment
    • Least time: Sends the request to server which has the fastest response time
    • Sticky Sessions: Sends the request to the same server that client was given last time
    • Hash: Define a key such as client IP address or request url to send to a particular server
    • Random:
  • Load balancing can happen at two layers

    • Layer 4
    • Layer 7 Preview
  • In Layer 4 loadbalancing, Load balancing can be done by redirecting the traffic recieved on a particular port of loadbalancer (source port) to particular port of connected servers (target port) Preview

  • Layer 7 loadbalancing Preview

Domain Names and DNS Servers

  • Generally we access the serves with names. There are two kinds of names depending on purpose

  • DNS is used to give names. It is like the phonebook (Telephone directory) of internet.

  • When i type google.com there will be some server which is hosting google.com and all communication protocols commmunicate mostly using ipaddresses not names.

  • So when i type name how does it gets converted to an IP Address, For this DNS Servers are maintained.

  • DNS server will store

    • records mapping name to ip address
  • Generally organization for their internal names use internal dns servers and websites use public dns servers. Preview

  • To store these Mapping DNS servers have different record types

    • A record: This record holds the ip address of domain Preview
    • CNAME Record: Forwards one domain name to other
    fb.com
    
    • MX record: Directs mail to email server
    • TXT record: lets admin store text in the records
    • NS Record: Stores the name server for DNS entry Preview
  • If it is private names for your network purpose we need to maintain dns entries

  • If it is for public website, we have Domain Name Sellers and hosting services like GoDaddy, AWS, Azure

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