I am making a a request to an image and the response headers that I get back are:
Accept-Ranges:bytes
Content-Length:4499
Content-Type:image/png
Date:Tue, 24 May 2011 20:09:39 GMT
ETag:"0cfe867f5b8cb1:0"
Last-Modified:Thu, 20 Jan 2011 22:57:26 GMT
Server:Microsoft-IIS/7.5
X-Powered-By:ASP.NET
Note the absence of the Cache-Control header.
On subsequent requests on Chrome, Chrome knows to go to the cache to retrieve the image. How does it know to use the cache? I was under the impression that I would have to tell it with the Cache-Control header.
You have both an ETag and a Last-Modified header. It probably uses those. But for that to happen, it still needs to make a request with If-None-Match or If-Modified-Since respectively.
To set the Cache-Control You have to specify it yourself. You can either do it in web.config , IIS Manager for selected folders (static, images ...) or set it in code. The HTTP 1.1 standard recommends one year in future as the maximum expiration time.
Setting expiration date one year in future is considered good practice for all static content in your site. Not having it in headers results in If-Modified-Since requests which can take longer then first time requests for small static files. In these calls ETag header is used.
When You have Cache-Control: max-age=315360000 basic HTTP responses will outnumber If-Modified-Since> calls and because of that it is good to remove ETag header and result in smaller static file response headers. IIS doesn't have setting for that so You have to do response.Headers.Remove("ETag"); in OnPreServerRequestHeaders()
And if You want to optimize Your headers further You can remove X-Powered-By:ASP.NET in IIS settings and X-Aspnet-Version header (altough I don't see in Your response) in web.config - enableVersionHeader="false" in system.web/httpRuntime element.
For more tips I suggest great book - http://www.amazon.com/Ultra-Fast-ASP-NET-Build-Ultra-Scalable-Server/dp/1430223839
Related
So with the Cache-Control response header i have seen a couple of different formats.
Like so
one website response (facebook)
cache-control: public,max-age=31536000,immutable
and another different website response
cache-control: max-age=31536000
cache-control: public,immutable
Does the header still work regardless of its formatting order or having multiple cache-control responses.
It is strange how websites set it differently and hard to know if it is working.
Maybe it sounds a novice question in Varnish Cache world, but why in WordPress it seems that is a need to install a external cache plugin, to working fully cached?
Websites are correctly loaded via Varnish, a curl -I command:
HTTP/1.1 200 OK
Server: nginx/1.11.12
Date: Thu, 11 Oct 2018 09:39:07 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Vary: Accept-Encoding
Cache-Control: max-age=0, public
Expires: Thu, 11 Oct 2018 09:39:07 GMT
Vary: Accept-Encoding
X-Varnish: 19575855
Age: 0
Via: 1.1 varnish-v4
X-Cache: MISS
Accept-Ranges: bytes
Pragma: public
Cache-Control: public
Vary: Accept-Encoding
With this configuration, by default WordPress installations are not being cached.
After test multiple cache plugins -some not working, or not working without complex configuration- i found the Swift Performance, in their Lite version, simply activating the Cache option, here really takes all advantages and here i can see varnish is working fully with very good results in stress test.
This could be ok for a single site on a single environment, but in shared hosting terms, when every customer can have their own WP (or other CMS) installation could be a problem.
So the key is there are no way to take full caching advantage from Varnish without installing 3rd party caching (and complex) plugins? Why not caching all by default?
Any kind of suggestions and help will be high welcome, thanks in advance.
With this configuration, by default WordPress installations are not being cached
By default, if you don't change anything in neither Wordpress or Varnish configuration, things would work together in a way that Wordpress pages are cached for 120 seconds. So real caching is possible, but it will be a short lived cache and highly ineffective one.
Your specific headers indicate that no caching should happen. They are either sent by Varnish itself (we're all guilty of copy pasting stuff without thinking what it does), or a Wordpress plugin (more often bad ones, than good). Without knowing your specific configuration, it's hard to decipher anything.
Varnish is a transparent HTTP caching proxy. Which means it’s just going to, by default, use HTTP headers, which are sent by backend (Wordpress), like Cache-Control, to make a decision on whether resource can be cached and for how long.
Wordpress, in fact, does not send cache related headers other than in a few specific areas (error pages, login POST submission, etc).
The standard approach outlined here is configuring Varnish with the highest TTL. With that:
Varnish has no idea when you update an article contents, or change theme. Typical solution to this lies in using cache invalidation plugin like Varnish HTTP Purge.
A plugin requirement comes from necessity to purge cache, when content is changed.
Suppose that you update a Wordpress page's text. You had that same page previously visited and it went into Varnish cache for storage. What happens upon the next visit, is that Varnish will serve the same, now stale content to all the next visitors.
The Wordpress plugins for Varnish, like Varnish HTTP Purge, will hook into Wordpress in a way that they will instruct Varnish to clear cache when pages are updated. This is their primary purpose.
That kind of approach (high TTL and cache purging) is de-facto standard with Varnish. As Varnish has no information about when you update content, the inner workings of purging cache is with the application itself. The cache purging feature is either bundled into CMS code itself (Magento 2, for example has it out of the box, without any extra plugins), or a Wordpress plugin.
I'm programmatically downloading a file from a Sharepoint 2016 document library. The URL goes:
https://hostname.com/Site/Folder/_layouts/15/download.aspx?{long, long URL}
The site emits the ETag header, but when I send a request with an If-None-Match, providing the ETag I just got, there's no 304 Not Modified response, it's 200 and the whole document again.
The ETag header I'm receiving goes:
ETag: "{EED54197-A30B-4625-9EBA-8DC7F9D62CF3},1435"
The request header then goes:
If-None-Match: "{EED54197-A30B-4625-9EBA-8DC7F9D62CF3},1435"
I'm testing the same setup against a static file in IIS - it works as expected, 304 comes.
What am I missing, please? Could it be an oversight in the Sharepoint API?
EDIT: one unsatisfactory workaround involves firing a HEAD request first and manually matching the ETag values on the client.
I'm bit confused with this header.
I already added "Expires" and "Cache-Control: max-age" in my .httaccess.
I also removed "E-tag" and "Last-Modified" as per advice:
If you remove the Last-Modified and ETag header, you will totally eliminate If-Modified-Since and If-None-Match requests and their 304 Not Modified Responses, so a file will stay cached without checking for updates until the Expires header indicates new content is available!
so why Google's PageSpeed shows that?:
Specify a cache validator:
The following resources are missing a cache validator.
Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources
I'm having trouble with a particular version of Pocket IE running under Windows Mobile 5.0. Unfortunately, I'm not sure of the exact version numbers.
We had a problem whereby this particular 'installation' would return a locally cached version of a page when the wireless network was switched off. Fair enough, no problem. We cleared the cache of the handheld and started sending the following headers:
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Last-Modified: Thu, 30 Jul 2009 16:42:08 GMT
The Last-Modified header is calculated on the fly and set to 'now'.
Even still, the handheld seems to be caching these pages: the page is sent with the headers but then when they disconnect the wireless network and click a link to the page (that was not supposed to be cached) it still returns this cached file.
Is there some other header/s that should be sent, or is this just a problem with Pocket IE? Or is it possibly something entirely different?
Thanks!
I'm not sure I can answer your question since I have no Pocket IE to test with, but maybe I can offer something that can help.
This is a very good caching reference: http://www.mnot.net/cache_docs/
Also, I'm not sure whether your example is the pasted results of your headers, or the code that you've set up to send the headers, but I believe the collection of headers in most language implementations (and by extension I assume most browser implementations) is treated as a map; therefore, it's possible you've overwritten "no-store, no-cache, must-revalidate" with the second "Cache-Control" header. In other words, only one can get sent, and if last wins, you only sent "post-check=0, pre-check=0".
You could also try adding the max-age=0 header.
In my experience both Firefox and IE have seemed more sensitive to pages served by HTTPS as well. You could try that if you have it as an option.
If you still have no luck, and Pocket IE is behaving clearly differently from Windows IE, then my guess is that the handheld has special rules for caching based on the assumption that it will often be away from internet connectivity.
Edit:
After you mentioned CNN.com, and I realized that you do not have the "private" header in Cache-Control. I think this is what is making CNN.com cache the page but not yours. I believe "private" is the most strict setting available in the "Cache-Control header. Try adding that.
For example, here are CNN's headers. (I don't think listing "private" twice has any effect)
Date: Fri, 31 Jul 2009 16:05:42 GMT
Server: Apache
Accept-Ranges: bytes
Cache-Control: max-age=60, private, private
Expires: Fri, 31 Jul 2009 16:06:41 GMT
Content-Type: text/html
Vary: User-Agent,Accept-Encoding
Content-Encoding: gzip
Content-Length: 21221
200 OK
If you don't have the Firefox Web Developer Toolbar, it's a great tool to check Response Headers of any site - in the "Information" dropdown, "View Reponse Headers" is at the bottom.
Although Renesis has been awesome in trying to help me here, I've had to give up.
By 'give up' I mean I've cheated. Instead of trying to resolve this issue on the client side, I went the server side route.
What I ended up doing was writing a function in PHP that will take a URL and essentially make it unique. It does this by adding a random GET parameter based on a call to uniqid(). I then do a couple of other little things to it: make sure I add a '?' or a '&' to the URL based on the existence of other GET parameters and make sure that any '#' anchor items are pushed right to the end and then I return that URL to the browser.
This essentially resolves the issue as each link the browser ever sees is unique: it's never seen that particular URL before and so can't retrieve it from the cache.
Hackish? Yes. Working? So far, so good.