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So let's talk about a routing policy

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that's super easy to understand,

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which is the latency-based routing policy.

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Okay.

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So now let's talk about latency-based routing policies.

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And the idea is that you want to redirect the resource

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that is going to have the lowest latency.

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So the closest to us,

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which is super helpful when latency is your main concern

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for your websites or applications.

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Now latency is going to be measured

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based on how quick it is for users to connect

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to the closest, identified AWS region for that record.

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So for example,

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if user in Germany and you have the lowest latency

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to a resource in the US,

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then this is where you will be redirected.

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And this can be combined with health checks that we'll see

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in the very next lecture.

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So let's have a look at the map of the world

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to understand it.

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Say we deploy our applications

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in two different parts of the world,

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one in us-east-1 and one in ap-southeast-1.

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Then the users are all around the world

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and the latency is going to be evaluated by Route 53.

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And so the users closest and with the lowest latency

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to the ALB, us-east-1, will be redirected there.

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Whereas, the other users will be redirected

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to ap-southeast-1.

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Now let's put this into practice in the console.

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So let's create new records.

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And the Record name is going to be,

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latency.stephanetheteacher.com.

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And the first Value is going to be the one

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in ap-southeast-1.

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So I'm good to paste the value in here.

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And then the Routing policy is going to be Latency.

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So when we do this thing,

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because we just put an IP address in here,

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we need to specify the region of our record.

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So this one is going to be corresponding

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to ap-southeast-1, which is at Singapore.

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Okay.

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And the reason is that Alias is not smart enough,

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at least in this stage,

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to take this IP and know that it comes from an EC2 instance

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that I have in Singapore,

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because this could be any IP in the world actually.

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So it's for us to specify,

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this IP corresponds to the region, Asia Pacific, Singapore.

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And then we can associate a Health check and a Record ID.

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So I'll call this one, ap-southeast-1.

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And it's just a name that I give it.

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Now we can add another record.

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Again, the Record name is going to be Latency

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and the value of which this one is going to be

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for us-east-1.

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So I'll have the Value here,

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and it's going to be Weighted.

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No, Latency. Excuse me, of course.

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And then it's us-east-1.

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And again, I will just have it as a us-east-1

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for my Record ID.

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And then one last record is going to be for eu-central-1.

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So I will copy this IP.

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And the Record name is this,

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the Value is here,

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the Routing policy is Latency

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and the Region is eu-central-1, so will be the Name.

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Okay.

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So as we can see, we have three records being created,

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successfully created, and this is it right here.

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And so now let's try them out.

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So right now I'm in Europe.

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And so if I open this,

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I'm expecting it to go to my instance in Europe.

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So I go to this URL,

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and I get a response, Hello World,

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from this IP in eu-central-1c.

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00:03:01,270 --> 00:03:03,910
If I use CloudShell to try it out

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and we do a dig command on this.

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00:03:05,940 --> 00:03:08,520
As we can see, we get an error code back of just one value.

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00:03:08,520 --> 00:03:09,353
Okay.

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00:03:09,353 --> 00:03:13,280
So just one value of the same IP address as this one.

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00:03:13,280 --> 00:03:15,800
So this is my instance in eu-central-1c.

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00:03:15,800 --> 00:03:16,938
And if I keep on refreshing,

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00:03:16,938 --> 00:03:19,500
because my latency hasn't changed to eu-central-1,

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I'm going to get, always the same answer.

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00:03:22,290 --> 00:03:23,123
Okay.

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00:03:23,123 --> 00:03:24,800
But, so how do we test whether or not

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that latency record is working?

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00:03:26,780 --> 00:03:28,380
Well, for this I can use a VPN.

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00:03:28,380 --> 00:03:31,410
And so let's go to Canada, for example.

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00:03:31,410 --> 00:03:34,180
And in Canada, it turns out that my latency

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is going to be the closest to the U.S.

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00:03:37,350 --> 00:03:38,913
So if I refresh this page now,

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00:03:40,360 --> 00:03:43,310
I get the Hello World from the U.S.

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00:03:43,310 --> 00:03:46,480
and when I did change my location, thanks to the VPN,

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00:03:46,480 --> 00:03:50,040
it cleared all the TTL that I had for my DNS cache,

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00:03:50,040 --> 00:03:50,873
locally on my laptop.

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00:03:50,873 --> 00:03:53,160
And so this is why automatically by refreshing it,

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00:03:53,160 --> 00:03:56,940
I was able to get the newest value for us-east-1a.

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00:03:56,940 --> 00:03:59,720
But again, if I use dig because this hasn't changed, okay,

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00:03:59,720 --> 00:04:02,030
my CloudShell is still in Europe, okay.

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00:04:02,030 --> 00:04:03,371
If I use the dig command

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00:04:03,371 --> 00:04:06,080
and use the exact same command as here,

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00:04:06,080 --> 00:04:08,620
I'm still going to get the exact same value as before, okay,

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00:04:08,620 --> 00:04:10,960
because, this computer right here,

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00:04:10,960 --> 00:04:12,857
this CloudShell sits in eu-central-1.

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00:04:12,857 --> 00:04:14,720
And so this is still the closest location

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00:04:14,720 --> 00:04:16,060
to eu-central-1.

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00:04:16,060 --> 00:04:18,670
And how do we test the one for AP Southeast?

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00:04:18,670 --> 00:04:19,973
Let's go into Hong Kong.

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00:04:25,360 --> 00:04:26,820
Okay. So I'm close to Singapore now.

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00:04:26,820 --> 00:04:28,650
And I will refresh this.

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00:04:28,650 --> 00:04:31,460
And the answer is, Hello World, from ap-southeast-1b.

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So the latencies record are working

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00:04:33,210 --> 00:04:34,240
and they're really, really good

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and very common to use online.

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I hope you liked it,

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and I will see you in the next lecture.