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‫So let's have a look

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‫at the caching behavior of our platform distribution.

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‫And this is the behavior I want to look at.

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‫So as you can see, we have the default behavior.

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‫It's a star.

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‫We can edit this,

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‫and we cannot edit the path pattern

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‫because this is the default behavior.

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‫Now if you scroll down, as you can see,

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‫we have cache key and origin request that we can set.

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‫And so we have a cache policy that we can define,

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‫and then we have an origin request policy that's optional.

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‫So let's go into creating a cache policy.

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‫So I call this one DemoCachePolicy.

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‫And as we can see here,

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‫we have control over the time to live settings.

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‫So we can set the minimum TTL,

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‫the maximum TTL, and the default TTL.

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‫And here we can have the cache key settings.

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‫So which headers do we want to include?

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‫And we can choose the headers from this list,

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‫or even add a custom header if we wanted to.

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‫Which query strings do we want to include?

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‫So all, or just maybe again,

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‫a list of query strings that we can add over here.

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‫And which cookies do we want to include?

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‫Again, all or a specified list.

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‫So here we can really specify what goes into our cache key.

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‫And then we know that data is going to be cached

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‫based on these settings for headers,

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‫query strings, and cookies.

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‫And we know for a fact that

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‫if we do select a cache key with some headers and so on,

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‫they are going to be passed to our origin request.

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‫But on top of it,

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‫if we wanted to also have extra headers passed

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‫or extra query strings passed to our origin request,

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‫we could create an origin request policy.

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‫So you will here you create

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‫a DemoOriginPolicy request policy.

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‫And here again we can specify

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‫which headers do we want to add into the request.

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‫So we have the headers,

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‫we have the query string facilities, and we have cookies.

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‫And this is to enhance our own little request in here.

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‫So back into the platform configuration.

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‫This is where we have the control

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‫over the cache keys and the origin requests.

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‫And hopefully, that makes sense to you now.

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‫So let me cancel this.

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‫The other thing I can do is to create

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‫a new behavior to override this behavior.

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‫So as you can see, I create a new behavior,

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‫and here I can say for /images/*,

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‫I want to send to a new origin.

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‫And of course you could define another S3 bucket

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‫as an origin or an EC2 instance,

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‫or whatever you want really.

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‫And again, you can have a specific cache key

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‫and origin request policy for this.

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‫And so your two cache behaviors will coexist.

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‫And, of course, the most specific is going

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‫to be the one that is going to be selected first.

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‫So here we have seen

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‫how to set up a behavior or multiple behaviors,

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‫and next we're going to have a look at invalidations.

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‫So first, let's observe the TTL setting

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‫by having this index.html file.

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‫And we're going to add some text to the title.

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‫Maybe I will add it, so let's go into index.html

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‫and it says instead of, "I really love coffee,"

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‫I say, "I really love coffee every morning."

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‫Okay, so we have updated this index.html file.

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‫What we're going to do now is to go into our S3 bucket,

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‫and we're going to upload a new version of that file.

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‫So because we haven't enabled versioning,

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‫actually this is going to replace that file.

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‫So we are uploading this index.html file here, upload.

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‫Now the upload has been succeeded.

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‫So if we click on this index.html and click on open,

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‫this is a opening directly from Amazon S3.

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‫So we get "I really love coffee every morning,"

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‫so we are getting the updated file directly into Amazon S3,

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‫but if we go into CloudFront and refresh this page,

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‫we're still getting just, "I really love coffee."

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‫The reason is CloudFront knows

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‫to cache the previous version for one day,

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‫and therefore CloudFront is not going to request

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‫from Amazon S3 this new file,

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‫"I really love coffee every morning."

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‫So how can we tell CloudFront

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‫to actually force fetching this new file version.

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‫Well, we go back into CloudFront,

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‫and we are going to go into the invalidations tab

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‫We're going to create an invalidation,

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‫and we'll just have a wild card, so a star.

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‫And this is going to say any object

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‫within the CloudFront cache should be removed.

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‫And then new objects are going

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‫to be fetched directly from Amazon S3.

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‫So let's go ahead and create this invalidation.

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‫So we can just do slash and then the star.

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‫Let's create this invalidation.

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‫And now that the invalidation is completed,

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‫what's going to happen is that if I go back

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‫to my CloudFront URL and refresh this,

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‫I'm gonna get, "I really love coffee every morning"

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‫because now the file has been

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‫correctly fetched from Amazon S3.

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‫So this shows you a demonstration

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‫of caching and invalidations.

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‫I hope you like this lecture,

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‫and I will see you in the next lecture.