Instructor: So now let's talk about routing policies
for Route 53.
So a routing policy is helping Route 53
respond to DNS queries,
and we shouldn't be confused about the word routing.
This is not like when you have a load balancer and the
actual load balancer will route traffic
to the backend EC2 instances.
No, no, no.
This routing is from a DNS perspective.
So the DNS does not respond, does not route any traffic.
So the traffic doesn't go through the DNS.
The DNS only will respond to the DNS queries
and then the clients will know to which way
they should be doing these HTTP queries, for example.
So the DNS just helps translate host names
into actual endpoints that the clients can use.
So Route 53 will support the following routing policy.
There's simple, weighted, failover, latency based,
geolocation, multi-value answer, and geoproximity.
And we're going to have a look at all of them
in this section.
So the first one is going to be the simple routing policy.
And the idea is that with this,
that we've actually been using before,
we're going to route traffic to a single resource typically.
So here's an example.
The clients that will say, hey,
I want to go to foo.example.com,
and Routes 53 will say, hey,
go to this IP address.
And this is an A record.
So it is possible for us to specify multiple values
in the same record.
And if so, if multiple values are returned by the DNS,
then a random one will be chosen by the clients
or client side.
So in this example,
we have the client's asking again for foo.example.com,
and Amazon Route 53 will just reply with three IP addresses
that occur embedded into the A record.
And then the clients will pick one of them randomly
and apply it for the routing.
So if you have enabled an alias record alongside
the simple policy,
then you can only specify on AWS resource as a target.
And finally, it's called simple because it's very simple.
And therefore you can not associate this with health checks
and we'll see health checks later on in this section
and how they work.
So let's go in the console to see how a routing policy
of step simple can be created.
So let's create a record, and the record name is going to be
simple.stephanetheteacher.com.
It's an A record, and the value of which is going to be,
for example, my instance in ap-southeast-1.
Now for TTL, it will say something very low,
like 20 seconds.
And the routing policy is going to be here.
So as you can see, we have different possibilities,
six of them, and then one other that is
somewhere else in the UI.
So we have a TTL 20 seconds as simple writing policy,
and let's just create this record.
So we've been doing this before.
We know how this works.
So now if we go to simple.stephanetheteacher.com.
And go to this URL, we get
Hello World from my instance in ap-southeast-1b,
which is awesome.
And if we do a dig command and have a look,
so we need to reinstall dig.
So sudo yum install bind-utils.
So this is because I restarted my machine here.
Okay, we're going to redo the dig command.
So we do the dig command on this.
As we can see, we have an A record of a TTL of 20 seconds
pointing to this IP.
But we can change this record now.
We're going to edit the record.
So I will just simply click on it and edit the record.
And for the value, now, I can enter multiple IPs.
So I can insert my one in ap-southeast-1
or one in us-east-1, for example.
So when I do so and save this,
what's going to happen is that once the TTL expires
from before, we're going to get two records back.
So let's use CloudShell to verify this.
So I'm going to do a dig command.
And as you can see,
now we have in the intersection, we have two responses.
We have one in this IP and one in this IP.
So it's a client side choice.
So that means that if I go to this website and refresh,
I have one chance out of two to go into us-east-1.
And I didn't.
So I was back into ap-southeast-1b,
but let me pause for 20 seconds and I'll get back to you.
And I'm refreshing.
And I get back the Hello World from us-east-1a.
So this worked.
This absolutely shows how simple records work.
I hope you liked it, and I will see you in the next lecture.