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In this new section of the course we'll cover some useful modules and directives outside of the fundamental

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engine configuration.

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And with the overall focus of the Course leaning toward Web servers a good starting point is configuring

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expires headers.

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Now if you're not familiar with expires headers they're essentially a response header informing the

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client or browser how long it can cached that response for.

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So for example let's say we have an image or more specifically a photo on our website that photo data

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isn't realistically going to change all that often meaning we can tell the browser to cache a copy of

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the photo for a relatively long time.

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And in doing so avoid any future requests for that photo drastically improving Web site load times and

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often overlooked a reduction in requests to our server.

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Another resource like a style sheet however which could very well change more frequently.

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We could say to a shorter time but still have the browser cache it none the less.

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Over to the configuration file as we lifted before and first thing I'll do is clean up some of these

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directives from the previous lesson then before we can figure out a way expires.

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Let's also as part of this lesson see how to set a generic response header in this thumb.

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Don't be in G location.

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I'll use the built in add header directive with the first argument being the header name my header and

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the second.

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The header value.

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Hello world.

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Save this reload the configuration and now to test this.

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We can make a cold request to thump or be in G with the flag for headers.

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I'll paste that you are L. enter and there we have it in the response headers.

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My header said to Hello World.

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So knowing how to said headers we can configure this location as a typical static resource by first

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setting the cache control header to public telling the receiving client that this resource or response

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can be cached in any way.

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Then the pragma header also to public.

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Essentially just an older version of this cache control header then else relate it but equally important

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header vary meaning the content of this response can vary with the value being xcept encoding.

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This is something we'll cover in more depth in the next lesson but essentially saying the response can

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vary based on the value of the request header except encoding.

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And finally to set the expires head up on this response.

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Engine X provides us a very convenient directive called expires.

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We could of course have said this header manually but there would be no logical way of setting a duration

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as the expires hid his value which needs to be a date.

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So with this expires directive we can simply sit a standard engine X duration for example 60 M which

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is 60 Minutes the same unit notations we used with the time out directives or 1 h for one hour.

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Or finally.

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In this case one m.

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Which in uppercase form is month.

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With this now you can see better why sit in an actual date.

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Wouldn't work.

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Let's say you sit in expires header using the ADD header directive with a date 1.

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Our way in the future that date would change in the configuration meaning in our time that date would

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be in the past whereas with this directive.

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Engine X sends the expires head of value as a date.

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This amount of time in the future for every request.

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Save this so we can test it reload.

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Make that same call request again and this time we get an expires header with the date set to exactly

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one month ahead of this recording including those additional headers we said and another cache control

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header added by the expires directive.

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Max h.

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With this being the number of seconds in 30 days or one month as we set it.

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This is essentially all this to configuring expires headers and given these new headers a browser will

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now cache this thumb or PRNG image locally meaning on the user's machine for this amount of time before

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requesting it from our server again before we finish up however let's see what a more typical location

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for such static resources might look like.

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First up I'll change this to be a case insensitive regular expression match looking to any request ending

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with an extension.

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So dot C S S J S J.

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B G or j peg or P E N G.

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You can of course add a bunch more year but this is the general idea.

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And not forgetting access underscore log off unless you really want to log each and every request.

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Save this reload the configuration and this time given that new location try style dotsie SS instead.

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Which now responds with those exact same expires headers.

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A simple but incredibly valuable addition to any Web server.