Route 53 Flashcards
1
Q
What is DNS?
A
- Domain Name System
- Like a phonebook
- DNS is used to convert human friendly domain names to Internet Protocol (IP) addresses (e.g. 82.124.53.1)
- IP addresses are used by computers to identify each other on the network. They come in two forms: IPv4 and IPv6
- IPv4 is 32 bits with 4 billions different addresses
- IPv6 is 128 bits with 340 undecillion addreses
2
Q
DNS: Top level domains
A
- Last word in the domain name represents the ‘top level domain’. The second word is known as the second level domain etc
- “.com”. “.edu” “.au”
- “.gov.uk” “.com.au”
- There is a database of top level domain names controlled by Internet Assigned Numbers Authority
3
Q
DNS: Domain Registrars
A
- An authority that can assign domain names directly under one or more top-level domains
- They are then registered with InterNIC, which enforces the uniqueness of domain names across the Internet. The database is called WHOIS
- Popular domain registrars include Amazon, GoDaddy, 123-reg.co.uk
4
Q
DNS: Name Server Records, A records
A
- Used by Top Level Domain servers to direct traffic to the Content DNS server, which contains the authoritative DNS records
- We type in a web address into our browser, then the top level domain is queried through the NS records to the SOA, which contains the DNSs
- An ‘A’ record is the fundamental type of DNS record. Stands for Address and is used by a computer to translate the name of the domain to an IP address
5
Q
DNS: TTL
A
- The length that a DNS record is cached on either the Resolving Server of the user’s own local PC is equal to the Time to Live (TTL) in seconds
- The lower the TTL, the faster the changes to DNS records take to propagate through the internet
- Default is 48, which means if you change you DNS it can take that long for the DNS change to propagate through the internet
6
Q
DNS: CName
A
- A Canonical Name can be used to resolve one domain name to another
- E.g. you may have a mobile website with the domain name http://m.acloud.guru used for users browsing from mobiles, and you might want http://mobile.acloud.guru to resolve to the same address
- Instead of having two separate IP addresses, you can map one to the other
7
Q
DNS: Alias Records
A
- Are used to map resource record sets in your hosted zone to Elastic Load Balancers, CloudFront Distributions, or S3 buckets that are configured as websites
- They work like a CName record, in that you map one DNS name to another target DNS name
- Key difference: a CName can’t be used naked domain names (zone apex record - the entire domain with the www or mobile infront)
- E.g. You can’t have CName for http://acloud.guru, it must either be an A record or an Alias
8
Q
DNS: Other points
A
- Elastic Load Balancers (ELBs) do not have predefined IPv4 addresses; you resolve them using a DNS name
- Given the choice, always choose an Alias Record over a CName
- Common DNS types: SOA Records, NS Records, A Records, CNames, MX records (for mail), PTR records (reverse of an A record, a way of looking up a name against an IP address)
9
Q
Registering a Domain Name
A
- Can buy from AWS directly
- It can take up to 3 days to register depending on the circumstances
10
Q
Route 53
A
- Amazon’s own Domain Name System (DNS)
- Enables developers to route end users to internet applications by translating web addresses to IP addresses
- Connects user requests to infrastructure running on AWS (as well as users to infrastructure to outside AWS)
11
Q
Route53 Routing Policies available on AWS
A
- Simple routing
- Weighted routing
- Latency-based routing
- Failover routing
- Geolocation routing
- Geoproximity routing (traffic flow only)
- Multivalue Answer routing
12
Q
Simple Routing Policy
A
- Can only have one record with multiple IP addresses
- If you specify multiple values in a record, Route 53 returns all values to the user in a random order
- Example: one DNS with three IP addresses in different regions. When we lower our TTL to one minute and wait for the cache to clear, we randomly get sent to different IP addresses
13
Q
Weighted Routing Policy
A
- Allows you to split your traffic based on different weights assigned
- E.g. set 20% of traffic to go to US-EAST-1 and 80% to go to US-WEST-1
- Health checks: are set on individual record sets. If a record set fails a health check, it will be removed from Route 53 until it passes the health check. SNS notifications can be set to alert if a health check fails
14
Q
Latency-based Routing
A
- Allows you to route your traffic based on the lowest network latency for your end user (i.e which region will give them the fastest response time)
- To you this routing, you create a latency resource record set for the EC2 instance (or ELB) in each region that hosts your website
- When Route 53 receives a query for your site, it selects the latency resource record set for the region that gives the user the lowest latency
- Route 53 then response with the value associated with that resource record set
15
Q
Failover Routing Policies
A
- Are used when you want to create an active/passive set up. E.g. you may want your primary site to be in EU-WEST-2 and your secondary DR site in AP-SOUTHEAST-2
- Route 53 will monitor the health of your primary site using a health check
- A health check monitors the health of your endpoints and will redirect if a health check fails
