Hi I'm using fragment caching extensively in my rails application. I've cached fragments which have user images in them. So when a user changes his/her avatar(image), a lot of fragments have to be expired. To solve this, I've made some settings so that a user's avatar URL is always constant ( "/avatars/:user_id/thumbs" ).
Im using amazon s3 for storage and the expires header for the images is "no-cache".
Sample image URL : https://s3.amazonaws.com/bucket_name/avatars/388/thumbs
In IE and Chrome, Im facing a peculiar problem. When a user changes his avatar, it is not reflected immiediately on client side. It takes 2-3 page refresh for the image to change. Has anyone faced similar issues before?
You're going about this the wrong way in my opinion. Expire the fragment as you're doing but allow rails' cache busting timestamps to force the browser to download new images.
e.g. s3.amazonaws.com/bucket_name/avatars/388/thumbs/filename.jpg?1230601161
Related
I'm using ActiveStorage for the first time.
Everything works fine in development but in production (Heroku) my images disappear without a reason.
They were showing ok the first time, but now no image is displayed. In the console I can see this error:
GET https://XXX.s3.amazonaws.com/variants/Q7MZrLyoKKmQFFwMMw9tQhPW/XXX 403 (Forbidden)
If I try to visit that URL directly I get an XML
<Error>
<Code>AccessDenied</Code>
<Message>Request has expired</Message>
<X-Amz-Expires>300</X-Amz-Expires>
<Expires>2018-07-24T13:48:25Z</Expires>
<ServerTime>2018-07-24T15:25:37Z</ServerTime>
<RequestId>291D41FAC6708334</RequestId>
<HostId>lEVGuwA6Hvlm/i40PeXaje9SEBYks9+uk6DvBs=</HostId>
</Error>
This is what I have in the view
<div class="cover" style="background-image: url('<%= rails_representation_path(experience.thumbnail) %>')"></div>
This is what I have in the model
def thumbnail
self.cover.variant(resize: "300x300").processed
end
In simple words, I don't want images to expire but to be always there.
Thanks
ActiveStorage does not support non-expiring link. It uses expiring links (private), and support uploading files only as private on your service.
It was a problem for me too, and did 2 patches (caution) for S3 only, one simple ~30lines that override ActiveStorage to work only with non-expiring (public) links, and another that add an acl option to has_one_attached and has_many_attached methods.
Hope it helps.
Your question doesn't say so, but it's common to use a CDN like AWS CloudFront with a Rails app. Especially on Heroku you probably want to conserve compute power.
Here is what happens in that scenario. You render a page as usual, and all the images are requested from the asset host, which is the CDN, because that's how it is configured to integrate. Its setup to fetch anything it doesn't find in cache from origin, which is your application again.
First all image requests are passed through. The ActiveStorage controller creates signed URLs for them, and the CDN passes them on, but also caches them.
Now comes the problem. The signed URL expires in 5 minutes by default, but the CDN caches usually much longer. This is because usually you use digest assets, meaning they are invalidated not by time but by name, on any change.
The solution is simple. Increase the expiry of the signed URL to be longer than the cache's TTL. Now the cache drops the cached signed URL before it becomes invalid.
Set the URL expiry using ActiveStorage::Service.url_expires_in in 5.2 or directly in Rails.application.config.active_storage.service_urls_expire_in in an initializer see this answer for details.
To set cache TTL in CloudFront: open the AWS console, pick the distribution, open the Behavior tab, scroll down to these fields:
Then optionally issue an invalidation to force re-caching of all contents.
Keep in mind there is a security trade-off. If the image contents are private, then they don't belong into a CDN most likely, and shouldn't have long lasting temp URLs either. In that case choose a solution that exempts attachments from CDN altogether. Your application will have to handle the additional load of signing all attached assets' URLs on top of rendering the relevant page.
Further keep in mind, that this isn't necessarily a good solution, but more of a workaround. With the above setup you will cache redirects, and the heavier requests will hit your storage bucket directly. The usual scenario for CDNs is large media, not lightweight redirects. You do relieve the app of handling a lot of requests though. How much that is a valid optimization should be looked into.
I had this same issue, but after I corrected the time on my computer, the problem was resolved. It was a server time difference, that the aws servers did not recognize.
#production.rb
Change
config.active_storage.service = :local
To
config.active_storage.service = :amazon
Should match aws/amazon whatever you defined it as in storage.yml
I'm trying to optimize my application in Ruby on Rails, and I realized that the pictures in my application is what most long does it take to load, but I also noticed another problem, which is that google chrome isn't caching the images.
I noted this because in the Google Developers Console you can see that Google Chrome makes a request to load the images that are canceled before the images are truly loaded.
This can be seen here, first I open the Google Developers Console, then refresh the page and within the first requests there you can see the ones of the images, but they are canceled immediately.
After that you can see the requests that actually loaded the images.
I don't understand why is this happening if in the response headers you can see that the Cache Control is set to public with max-age = 31536...
I put the images in my application this way:
<div class="col-xs-3"><%= image_tag "#{#hero.id}/ability_1.png", class: "center-block"%></div>
And the images are organized in folders in app/assets/images
Is there a RoR way to fix this?
Edit: Now testing my app (which is in Heroku) in Windows I noticed that in fact Google Chrome caches the images sometimes, but it happens like the 50% of the times (and when I was in Ubuntu in development it didn't work a single time), while in firefox the first time the images are loaded, but the subsequent times I load the same view I can't even notice the reload, it's beatiful, Why google Chrome is not like that? Is normal that Google Chrome acts so weird?
The most important thing to realize when analyzing browser caching is the "Status Code". In your example, you can see you got a "304", which stands for "Not Modified" Which means the browser "could potentially use it's cache". So you ARE in fact caching. Caching != Not hitting your web server.
The definition according to Mozilla:
This is used for caching purposes. It is telling to client that response has not been modified. So, client can continue to use same cached version of response.
It sends the etag and last-modified to your web server, and your web server then looks at those meta and say "Nope, this file hasn't changed, so feel free to use your cache", and that's it. It actually does not send the file again. You can see that the "Size" is much less then when it's a "200" status code, where the web server IS sending the file, and the timing should me much shorter as well.
In Chrome you can force "non-caching" by checking the "Disable cache" option in the Network tab.
Hope that helps!
It looks like Chrome does handle image caching differently. What type of reload are you doing (following links, pressing enter in the address bar, Ctrl+r)? It looks like if you press enter in the search bar it will respect max-age but if you use Ctrl+r Chrome sets max-age to 0.
expires_in max-age cache control doesn't work
Chrome doesn't cache images/js/css
You can force caching with manifest file. There's plenty of docs on the web about the topic. Here's a starter: http://www.w3schools.com/html/html5_app_cache.asp
the request headers contain max-age=0. Try setting that to a big number!
My heroku application resizes images as thumbnails: these thumbnails are supposed to be stored by Cloudfront.
Requesting the thumb to Heroku will cause a image to be generated, which takes time, and should only be done once for each image.
Our application always access these images through Cloudfront: so the images should be generated once, then they'd be stored by Cloudfront which would serve us as long as the cache would be deemed valid.
We receive mails everytime a thumb is generated. The problem is, when we try to access those thumbs, our Heroku server is asked to generate the thumbnail again: only then the thumb is properly cached, and we can freely access it without any traffic being sent to our server.
Does anyone know why such a thing would happen ?
On the app I am working on I just implemented fragment caching for a threaded activity flow. Each thread is cached I gained almost 50% in processing time and it works fine, but a side effect I didn't anticipate is that amazon s3 links to attachments expire.
How can I have the links regenerated on each page refresh and at the same time avoid having to reload the whole conversation? In other words, is there some sort of after_filter :regenerate_uploads I can do through rails or javascript.
I'm totally new to caching so I may be missing some details or clarity, so please help me reformulate my question if needed
In my web app each user will be having a profile image those images are stored in Amazon s3. If the user signs in i need to show that image and that will stay in the side bar in all the pages he enters. Once he signs in is there anyway i can cache the image so that i no need to get back from Amazon s3 every time ? when he again updates the image i need to clear the cache.
You can use standard Http Caching for this.
You should set the Cache-Control and/or expires headers depending on your needs.
All the major S3 clients support setting these headers or you can set using the S3 API's or SDKs/Libraries etc.
In order to re-download the image if it has changed, you can add a querystring to the url.
eg
http://mypath/myfile.ext?v=1
http://mypath/myfile.ext?v=2