HTTP Caching - Revision history

Thexa4 at 02:13, 19 January 2021

2021-01-19T02:13:53Z

← Older revision		Revision as of 19:13, 18 January 2021
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	* Don't put data that changes independently into the same request. Instead use a resource that returns [[URL \| URLs]] to the child requests and leverage HTTP2 and caching.		* Don't put data that changes independently into the same request. Instead use a resource that returns [[URL \| URLs]] to the child requests and leverage HTTP2 and caching.
	* Instead of disabling caching, set the <code>maxage</code> to a low value like 5 seconds.		* Instead of disabling caching, set the <code>maxage</code> to a low value like 5 seconds.


			[[Category: Terminology]]

Thexa4: /* ETag Based Caching */

2021-01-19T01:19:56Z

ETag Based Caching

← Older revision		Revision as of 18:19, 18 January 2021
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	If it is easy to generate a unique identifier that always changes when the response changes you can use that as an ETag identifier. This is done using the [[ETag Header]]:		If it is easy to generate a unique identifier that always changes when the response changes you can use that as an ETag identifier. This is done using the [[ETag Header]]:

	ETag: W/"my-unique-identifier"		ETag: W/"my-unique-identifier"
	Cache-Control: public,maxage=5,must-revalidate		Cache-Control: public,maxage=5,must-revalidate

	This example will ask the cache to keep serving this response to requests coming in in the next 5 seconds. If a matching request comes in after the five seconds the cache will check whether it still has the last version using the [[If-None-Match header]].		This example will ask the cache to keep serving this response to requests coming in in the next 5 seconds. If a matching request comes in after the five seconds the cache will check whether it still has the last version using the [[If-None-Match header]].

Thexa4: /* Time Based Caching */

2021-01-19T01:11:12Z

Time Based Caching

← Older revision		Revision as of 18:11, 18 January 2021
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	== Time Based Caching ==		== Time Based Caching ==
	An easy way to implement caching is by specifying that a response is valid for a certain amount of time. For example if your resource is static and the same for all users you can set the following [[Cache-Control ~~Header~~]]: <code>Cache-Control: public,maxage=300</code> This will keep the resource in your cache for five minutes.		An easy way to implement caching is by specifying that a response is valid for a certain amount of time. For example if your resource is static and the same for all users you can set the following [[Cache-Control header]]: <code>Cache-Control: public,maxage=300</code> This will keep the resource in your cache for five minutes.

	== ETag Based Caching ==		== ETag Based Caching ==

Thexa4: Created page with "One of the often overlooked superpowers of HTTP is the built in support for caching. This allows you to only spend the effort of generating a response every so often inste..."

2021-01-19T01:10:31Z

Created page with "One of the often overlooked superpowers of HTTP is the built in support for caching. This allows you to only spend the effort of generating a response every so often inste..."

New page

One of the often overlooked superpowers of [[HTTP]] is the built in support for caching. This allows you to only spend the effort of generating a response every so often instead of having to generate it for each user individually. HTTP caching is one of the main strategies used in achieving [[Scaling | scale]] and is also very important when improving performance.

== Types of Caches ==
A HTTP cache is either a public or a private cache. A private cache is defined to only be used by one user. An example of a private cache is the browser cache. Private caches can cache both public and private responses.

Public caches are usually shared between multiple users. This means that any data you cache here should not contain sensitive or user-specific data. Examples of public caches are company wide caches, or caching proxy like [https://varnish-cache.org/intro/index.html Varnish] you can deploy in front of your webserver. Public caches will only return cache items that are marked as public.

== Time Based Caching ==
An easy way to implement caching is by specifying that a response is valid for a certain amount of time. For example if your resource is static and the same for all users you can set the following [[Cache-Control Header]]: <code>Cache-Control: public,maxage=300</code> This will keep the resource in your cache for five minutes.

== ETag Based Caching ==
If it is easy to generate a unique identifier that always changes when the response changes you can use that as an ETag identifier. This is done using the [[ETag Header]]:

ETag: W/"my-unique-identifier"
Cache-Control: public,maxage=5,must-revalidate

This example will ask the cache to keep serving this response to requests coming in in the next 5 seconds. If a matching request comes in after the five seconds the cache will check whether it still has the last version using the [[If-None-Match header]].

== Browser Refresh ==
When you press F5 in a browser it will resend the request with a <code>Cache-Control: no-cache</code> header. This asks all caches in between to return a fresh response. Beware that this might not work if you use a cache that does not adhere to the standard like Cloudflare.

== Vary ==
The [[Vary header]] indicates how requests are matched to requests. If the [[URL]] and the varied headers match the response can be returned. If you have a [[HATEOAS Api]] you generally want to vary on the following headers:
* Accept
* Accept-Encoding
* Accept-Language (if you have a multilingual endpoint)

Never add the [[User-Agent header]] though! This will likely make your website slower than not having a cache because of the huge amount of cache entries this can result in.

== General Strategies ==
* Separate user data from static data.
* Put data that changes together into the same [[resource]].
* Don't put data that changes independently into the same request. Instead use a resource that returns [[URL | URLs]] to the child requests and leverage HTTP2 and caching.
* Instead of disabling caching, set the <code>maxage</code> to a low value like 5 seconds.