![]() ![]() HTTP response headers like Etag and Last-Modified allow web servers to identify when a resource has last changed. When the cache receives an 304 Not Modified response, the time to live that is defined by the Cache-Control or Expires header will be used to set the lifetime of the object after revalidation. This reduces the amount of data sent over the wire, and it can also result in a lower server resource consumption at the origin level. #Private cache software codeIf the resource hasn’t changed, a 304 Not Modified status code will be returned without a response body. This means that the origin web server will only send the payload if the requested resource has changed. Revalidation can also be done conditionally. This is discussed in the cache revalidation part of the HTTP caching flow section. However, the HTTP protocol allows you to control the cacheability under the form of specific header syntax.Ĭaches are also allowed to serve stale content while revalidation takes place. These rules can be specifically enforced in the implementation or configuration of the cache. On the other hand, you can decide whether or not to serve a cached response from the cache. On the one hand you can decide whether or not to store a response in the cache. If the returned response uses a Set-Cookie header to change state, the response shouldn’t be cached. If the type of request (for example an HTTP POST request) implies a change of the resource, it shouldn’t be cached either. Not all HTTP responses can or should be cached: if the content is private, it should not be stored in the cache. However, there are also specific instructions that only apply to proxies. HTTP’s caching policies allow HTTP responses to be cached by both clients and proxies using the same syntax. Nowadays reverse caching proxies are put in front of the origin web platform to protect it against traffic spikes and prevent the platform from caving in under pressure. ![]() As a consequence, caching proxies also shifted. Instead the increase of bandwidth shifted the pressure from the client to the server: traffic spikes started jeopardizing the stability of servers. Another disadvantage is the fact that the cache is hosted locally, which means there is a cache per user.īy installing proxy servers closer to the user, either in the office or at the internet provider’s data center, clients can retrieve centrally cached copies of the requested content and act on behalf of the origin web server.Īs broadband internet became more common, local caching proxy servers were no longer crucial. Unfortunately browser cache is not reliable: users can flush the cache at any time, and they can even disable the cache. Being able to cache HTTP responses in the browser avoided expensive HTTP roundtrips. In the early days of the web, bandwidth was limited. Historically HTTP responses were cached by the web browser to reduce network traffic. HTTP caching reduces network traffic and server load, which results in lower response times. By caching the response, clients don’t have to connect to the web server every time they want to access that content. HTTP has caching capabilities built into the protocol to ensure that clients or proxies can store the HTTP response in the cache for a certain amount of time. ![]() There are even standardized headers that are part of HTTP’s specification that will allow you to control the behavior of a web cache. Whether this HTTP cache is a reverse caching proxy like Varnish or a full-blown CDN, you need to understand the rules of the game, and you need to understand the basics of HTTP caching. It’s important to understand HTTP caching because at some point an HTTP cache will protect your web platform from going down. ![]()
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