AWS Certified Architect Associate VPC Study Sheet

AWS VPC

As a Network Engineer; it fascinates me what Amazon has done to virtualize the Network in its Virtual Private Cloud.   Here go the notes!

AWS VPC is a logically isolated section of the AWS Cloud, a virtual network in which you can launch your EC2 instances that can be private or public.

All AWS VPCs contain: subnets, route tables, DHCP option sets, Security Groups and ACLs.

Optional VPC elements are: Internet Gateways, Elastic IP. Elastic Network interfaces, EndPoints, Peering, NAT servers or Gateways, Virtual Private Gateway, Customer Gateways, and VPNs.

Largest Subnet in a VPC is /16  Smallest Subnet is /28.

One Subnet per one Availability Zone; and do not span Availability Zones 

VPC Route Tables:

VPC has a Router (Implicit).

VPC comes with a “Main” Route table which you can change; and you can also create separate routes tables within your VPC that are not associated with “Main”.  Each subnet you create has to be associated with one of the route tables.

VPC Internet Gateways [ IGW]:

An AWS VPC Internet Gateway is a Horizontally Scaled, redundant, highly VPC component that allows communication between your EC2 instances and the internet. [ Basically default route Target out points to the IGW ]

IGW’s must be attached to VPCs

Route table must have a 0.0.0.0/0 route to send all non-VPC traffic out.

ACLs and Security Groups MUST be configured so the bad guys don’t get in .

Below image is from AWS: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Internet_Gateway.html

VPC DHCP Option SETS

AWS automatically creates and associates a DHCP Option Set for your VPC and sets two options: 1. DNS servers 2. Domain-Name. These are set to Amazon default DNS and Domain name for your region.  To assign your own Domain name; you can create a custom DHCP option set and configure the following:

  1. DNS servers
  2. Domain-Name
  3. NTP Servers
  4. NetBios Name servers
  5. NetBios Node type.

Elastic IP addresses [ EIP ]: 

These are AWS Public IP Addresses that you can allocate to your account from their larger pool; reachable from anywhere on the internet.

  • Create the EIP first for your VPC; and then assign it to an EC2
  • EIPs are specific to a region
  • One to one relationship between network interfaces and EIP
  • EIPs can be moved from one EC2 instance to a different EC2 instances.
  • EIPs remain with your account until you release them.
  • There are charges incurred fro EIPs allocated to your AWS account; when they are not in use.
  • charged when instance is stopped; charged when un-attached
  • Free only only one EIP per instance and instance is running.

Elastic Network Interfaces [ EIN ]:

This is a network interface available within a single VPC that can be attached to an instance; and are associated with a subnet when they are created

  • Can have one public and multiple private IPs
  • Can exist independently of Instance
  • Allow you to create a management Network, use Network and Security AMIs/Appliances create dual-homed solutions.

VPC EndPoints

VPC Endpoints allows you to create a private connection between your VPC and other AWS servers without going over the internet. Works with Route TAbles; where Endpoint for particular service can be a target.

VPC Peering

Allows for communication between two VPCs; e.g., communication from instances in one VPC to instances in another VPC.

  • you can create peering with your VPC and:
    • another VPC in your account
    • VPC in another AWS account
  • within a single region

Peering Rules:

  • no peering between VPC that have matching over overlapping CIDR blocks
  • cannot peer with VPC in different Regions
  • No transitive peering
  • No more than one peering connection between two VPCs

Security Groups (SG) in a VPC

A security Group is a stateful Firewall that controls inbound and outbound network traffic to individual EC2 instances and other AWS resources.  All EC2 instances must be launched into a Security Group. Only the Default Security Group  allows communications between all resources in that same Security Group . Instances in Security Groups you create cannot talk to each other by default.

  •  500 SGs per AWS VPC
  • 50 inbound, 50 outbound rules for each SG
  • 5 SG’s per network interface
  • applied selectively to individual instances
  • Can specify ALLOW rules / but no DENY [ whitelist ]
  • By default, no inbound traffic is allowed from anything not in SG
  • New SGs by Default have a permit all outbound.
  • Stateful
  • Evaluates ALL rules before deciding permit / deny

Network Access Lists (ACLs)

so you Cisco guys, this is pretty much the same. . .

Subnet Level, state-less, number set of rules, processed top down.  VPCs have a default ACL associated with every subnet that allows all traffic in and out. When you crate an ACL, its deny all until you create rules.

  • Supports allow Rules and Deny rules
  • State-less, return traffic MUST be called out
  • processed in order
  • Because at Subnet level, applied to all instances in that subnet

NAT Instances ( AMI ) on VPC

AMIs on AWS that have the amzn-ami-vpc-nat – use is taking traffic from private subnet in VPC and forwarding it to the IGW ( Internet Gateway ) .

You need a SG will appropriate Rules / in and out

Launched in a PUBLIC subnet in VPC

-Disable Source / Destination Check of NAT or it won’t work 

Subnet with PROV host will have NAT host as the destination in the route table:

0.0.0.0/0 goes to > [NAT instance name]

NAT Gateway on VPC

Designed to operation like the NAT AMI, but easier to manage; ( no EC2 isntance to patch ); and highly avaialble within an AZ.

VPN, VPG and CGW in a VPC

A VPG ( Virtual Provate Gateway ) is the VPn concentrator on the AWS side of a VPN connection.

A CGW represents a physical device on the customer’s network; thier end of the tunnel.

The VPN handshake must be initiated on the customer’s side.

EC2 Virtualized Types

Hardware Virtual Machines  (HVM) vs. ParaVirtual Machines  (PV)

HVM AMIs – fully virtualized set of hardware and boot executes master boot record of block device of image; has support for special VM extensions ( GPU accelerator ).

PV-AMI – Use PV-GRUB boot loader; runs on hardware without explicit support for VM; but no special extensions; currently only C3 and M3 types can be used.

T2 instances must be launched into a VPC ( not supported in classic )

T2 must be on HVM AMI

Recommended use current generation instance types on HVM AMIs

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