I wouldn't cache on disk since I think it would eat resources that otherwise would be used for other application caching.

For the same reason it's not smart to log to disk in Azure.

Haven't used ImageResizer but I see there's a blob storage plugin available: https://imageresizing.net/docs/v4/plugins/azurereader2

The files are read from blobstorage before being transformed. I think the recommended way of using imageresizer in azure is diskcache and a CDN.

I would like to skip the CDN if possible, or only use the CDN for episerver media and not the entire site. Is that even possible?

/Peter

Gotcha.

With https://github.com/bjuris/EPiServer.CdnSupport you can rewrite (only) all media URLs to an absolute "CDN" or other proxy type URL.

So using only DiskCache in Azure is not going to give acceptable performace?

/Peter

It's not recommended to use and fill up disk in an Azure Web App for any use case so I wouldn't take that road.

I haven't had any problems using only DiskCache in an Azure web app. That was however a quite small, low traffic site.

Ok, do you have DiskCache autoClean enabled when running in Azure?

/Peter

I'm pretty sure that it wasn't enabled. Not even sure it was available at that time (approx. two years ago).

We have used ImageResizer in Azure quite a few times, also for quite big sites. I haven't noticed any performance problems using the DiskCache plugin.

Disk cache plugin is quite problematic on Azure when you have too many images and your site is under heavy load. I have experienced the site running out of disk space (even with a CDN sitting in front of it). We have an Azure site with 50 GB storage, but the disk filled up in less than two days. After that we have to disable the disk cache plugin, and rely solely on the CDN to cache the images.

The CDN is the absolutely must have thing, because Image resizing operation eats up a large chunk of CPU time and memory. You'll bring your web server to its knee without the CDN.

1. Get CDN. Rewrite your image urls is fastest way to support it. Use unique urls with a hash. There is a nuget package for it. 
2. Use Image Resizer as usual but without disc cache. 

The Picture helper renders a picture element. The picture element presents a smorgasbord of images in different sizes and formats. It’s then up to the browser to select the most appropriate image depending on screen resolution, viewport width, network speed, and the rules that you set up.