‫So let's talk about a routing policy
‫that's super easy to understand,
‫which is the latency-based routing policy.
‫Okay.
‫So now let's talk about latency-based routing policies.
‫And the idea is that you want to redirect the resource
‫that is going to have the lowest latency.
‫So the closest to us,
‫which is super helpful when latency is your main concern
‫for your websites or applications.
‫Now latency is going to be measured
‫based on how quick it is for users to connect
‫to the closest, identified AWS region for that record.
‫So for example,
‫if user in Germany and you have the lowest latency
‫to a resource in the US,
‫then this is where you will be redirected.
‫And this can be combined with health checks that we'll see
‫in the very next lecture.
‫So let's have a look at the map of the world
‫to understand it.
‫Say we deploy our applications
‫in two different parts of the world,
‫one in us-east-1 and one in ap-southeast-1.
‫Then the users are all around the world
‫and the latency is going to be evaluated by Route 53.
‫And so the users closest and with the lowest latency
‫to the ALB, us-east-1, will be redirected there.
‫Whereas, the other users will be redirected
‫to ap-southeast-1.
‫Now let's put this into practice in the console.
‫So let's create new records.
‫And the Record name is going to be,
‫latency.stephanetheteacher.com.
‫And the first Value is going to be the one
‫in ap-southeast-1.
‫So I'm good to paste the value in here.
‫And then the Routing policy is going to be Latency.
‫So when we do this thing,
‫because we just put an IP address in here,
‫we need to specify the region of our record.
‫So this one is going to be corresponding
‫to ap-southeast-1, which is at Singapore.
‫Okay.
‫And the reason is that Alias is not smart enough,
‫at least in this stage,
‫to take this IP and know that it comes from an EC2 instance
‫that I have in Singapore,
‫because this could be any IP in the world actually.
‫So it's for us to specify,
‫this IP corresponds to the region, Asia Pacific, Singapore.
‫And then we can associate a Health check and a Record ID.
‫So I'll call this one, ap-southeast-1.
‫And it's just a name that I give it.
‫Now we can add another record.
‫Again, the Record name is going to be Latency
‫and the value of which this one is going to be
‫for us-east-1.
‫So I'll have the Value here,
‫and it's going to be Weighted.
‫No, Latency. Excuse me, of course.
‫And then it's us-east-1.
‫And again, I will just have it as a us-east-1
‫for my Record ID.
‫And then one last record is going to be for eu-central-1.
‫So I will copy this IP.
‫And the Record name is this,
‫the Value is here,
‫the Routing policy is Latency
‫and the Region is eu-central-1, so will be the Name.
‫Okay.
‫So as we can see, we have three records being created,
‫successfully created, and this is it right here.
‫And so now let's try them out.
‫So right now I'm in Europe.
‫And so if I open this,
‫I'm expecting it to go to my instance in Europe.
‫So I go to this URL,
‫and I get a response, Hello World,
‫from this IP in eu-central-1c.
‫If I use CloudShell to try it out
‫and we do a dig command on this.
‫As we can see, we get an error code back of just one value.
‫Okay.
‫So just one value of the same IP address as this one.
‫So this is my instance in eu-central-1c.
‫And if I keep on refreshing,
‫because my latency hasn't changed to eu-central-1,
‫I'm going to get, always the same answer.
‫Okay.
‫But, so how do we test whether or not
‫that latency record is working?
‫Well, for this I can use a VPN.
‫And so let's go to Canada, for example.
‫And in Canada, it turns out that my latency
‫is going to be the closest to the U.S.
‫So if I refresh this page now,
‫I get the Hello World from the U.S.
‫and when I did change my location, thanks to the VPN,
‫it cleared all the TTL that I had for my DNS cache,
‫locally on my laptop.
‫And so this is why automatically by refreshing it,
‫I was able to get the newest value for us-east-1a.
‫But again, if I use dig because this hasn't changed, okay,
‫my CloudShell is still in Europe, okay.
‫If I use the dig command
‫and use the exact same command as here,
‫I'm still going to get the exact same value as before, okay,
‫because, this computer right here,
‫this CloudShell sits in eu-central-1.
‫And so this is still the closest location
‫to eu-central-1.
‫And how do we test the one for AP Southeast?
‫Let's go into Hong Kong.
‫Okay. So I'm close to Singapore now.
‫And I will refresh this.
‫And the answer is, Hello World, from ap-southeast-1b.
‫So the latencies record are working
‫and they're really, really good
‫and very common to use online.
‫I hope you liked it,
‫and I will see you in the next lecture.