Show HN: Dynamic image size generator | Hacker News Reader

Show HN: Dynamic image size generator

21 pointsryan2103014 comments

Hi,

Firstly, the link to the tool - https://github.com/DrRoach/DynamicImage

I created a dynamic image sizing tool that allows images of any size to be generated on the fly. It's aims are as follows:

a) Allow users of sites to upload images of any size without the site owner having to worry about their dimensions or having to resize them.

b) Reduce load times for sites as images can be stored on their own dedicated server and be served in milliseconds.

I'd love to hear some feedback as to what you think and whether you'd consider using this tool and if not, why not?

All constructive criticism is welcome!

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Thumbor is an awesome open source solution which has proved itself in many high traffic sites.

https://github.com/thumbor/thumbor

Nice! This is definitely an important tool when creating a site traffic in images to be displayed across a variety different sized screens. Having worked on this type of project before I'll mention a few challenges you have not yet addressed.

At some scale point, your single DynamicServer server will have more resize requests than it has CPU cycles to serve. The straightforward solution will be to add more DynamicServer instances. This means that your source image directory will have to be accessible from both instances. It also duplicates your cache directory, meaning a single image size could get generated on both servers. You might solve that by having a shared image cache network directory. Another solution could be to use a hash mechanism to determine a particular backend server from the load balancing layer, so any particular image would always be generated on the same instance.

Something interesting happens when people upload an image to their newsfeed. If it's a public newsfeed, there can be a good many requests of the image within the next several seconds at upload. This means that you can get multiple cache miss requests at the same time coming into your DynamicImage server. Your PHP processes are vertically partitioned, so your server will be simultaneously generating the resize. For users with only a few friends, this is a small waste of CPU cycles, but for users with massive user bases (e.g. Britany Spears), a single upload could grind your DynamicImage server to a halt just because of simultaneous duplicated work. Varnish (and other load balancers) can solve this by collapsing multiple requests to the same resource into a single HTTP call (https://varnish-cache.org/docs/3.0/tutorial/handling_misbeha...).

I've created scripts like these as part of our home-brewed CMS system in the early 2000's.

Nice and easy dos tool. Enumerate the width and height parameters and bring down the server fast.

Better way to do it is to specify, or allow admins to specify, a set of named sizes and only allow these named sizes.

You could also think about adding parameters to determine the crop, or force aspect ratio etc. (with the same risk of dos)

Having the resizing api exposed publicly lile in the ajax example is definately a bad idea.

The second example (labeled "html") demonstrates using it entirely serverside, which would be fine. That way, only the filename of the cached file is exposed.

...Which was how I did it in the late 90's.

I did both and used a .htaccess rule to look for a sharded filepath based on the hash of the image requested and parameters in the url.

So you could o a1jjajda.jpg?size=200x150 and it would check for the existence of a/l/jjajda/200x150.jpg and if it didn't exist it would create it from a/l/jjajda/original.jpg store it at the right place and serve it.

.htaccess file looks meant I didn't have to boot PHP to serve an image the second time (we where using laravel and even optimised it takes 30-40ms to come up) and in 95% of cases at all (particulary since I then wrote a shell script that trawled the paths, built a list of common sizes and named presets and requested them when the server was quiet).

It worked out pretty well actually and had the benefit of relying on extremely robust and well tested technology.

That was some hinky looking regexs though.

    RewriteCond %{QUERY_STRING} ^presets=([a-zA-Z0-9_]+)?$
    RewriteRule ^files/(.*)/(.*)/(.*)/(.*) files/$1/$2/$3/%1_$4? [L,QSA]

    RewriteCond %{QUERY_STRING} ^options=[\[|\{]?([0-9]*x[0-9]*)[\]|\}]?$
    RewriteRule ^files/(.*)/(.*)/(.*)/(.*) files/$1/$2/$3/%1_$4? [L,QSA]

Thats exacly how I did it, and than the creation of a new cached file was handled by a PHP script ran as the 404 errorHandler which output the image to both the browser and file system.

Still pretty dangerous stuff i.e. ?size=10000x2000000

Nah, I'm a cynical fucker, I had...

    $x = $x > 9000 ? 9000 : $x;
    $y = $y > 9000 ? 9000 : $y;

I also had checks for negative values and that what I got actually made sense as an integer, since well it's the internet and a get request, they can put anything.

Tbh even 81MP was pushing it but I got to put the comment

// check and limit maximum image size // it's over 9000!

As someone who was around online back then how could I resist.

EDIT: Just remembered, I had to really resist the urge to change the returned image to a raised middle finger if either parameter was out of limit, not because I didn't think it was funny but because with my luck it'd be me that fat fingered it.

Nginx has a module for this which you can tie into your cache: http://charlesleifer.com/blog/nginx-a-caching-thumbnailing-r...

I was playing around with some image optimization libraries a few weeks ago. This looks handy, but my wish list also includes image optimizations to reduce file size.

If people are looking for a third party service that does this I would recommend cloudinary.com

There are SaaS for that, Uploadcare offers that for free, for instance

Good deal for a small site, but if you have traffic, it gets expensive fast. $.25/GB bandwidth vs $.085/GB from Cloudfront va $.06 at a budget CDN.

imgix is an image CDN service (not free) that offers this feature and more. Not usually used for personal projects I guess since there is no free tier for it.

Imgix is great, but expensive as a cdn + image size on the fly company. I have been testing then for ~6 months for thumbnail generation but will be transitioning off soon. The cost is running about half of my S3 storage and transfer bill for only generating thumbs.

It's hard to justify not just creating my own thumbnails and stashing them on S3 for my use case.

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