Networking Services¶

Route53¶

DNS uses UDP, but uses TCP when size > 512 or for tasks like zone transfers
Route53 will incur a charge for CNAME but not for an Alias
Resolving name server: A server (by ISP or public) that resolves domain name via chain:
- Root server -> TLD server -> name server
Zone file: A name server’s file containing mapping between IP and domain
Hosted Zones: Like Zone file, but hosted on AWS. Must have the same domain name.
- Starts with SOA record
- Private: routing within VPC
- Public: routed to internet
- Use ALIAS, since CNAME are not allowed in
Max Soft limit of 50 domain names
Routing policies
- Simple: one domain points to one server
- Weighted: split based on weight to different servers (eg for A/B testing)
- Latency: pick server that has lowest latency to the user
- FailOver: pick secondary server when primary fails. Must set up health check for primary.
- Geo location: pick based on user’s geo location. Can specify, continent, country, US states or any (*)

Operates at instance layer, associated with Networking Interface (first line of defense)
Control Inbound and outbound ports
Default outbound is all, inbound is none
Source can be IP, CIDR (0.0.0.0/0 => public) or SG
- Can’t block specific IP
Security Group changes are immediate
Up to 5 SG can be assigned to an instance

Security Group	Network ACL
Instance level	subnet level
stateful	stateless
only allow rules	allow and deny rules
all rules are evaluated	rules applied with lowest seq # first
applied to instance only if SG specified	applied to all instances within subnet