Shared file storage on a web cluster.

 

Part of my web app allows users to upload their own avatars as a GIF/PNG/JPG. It then resizes the pic automatically, saves out the file (and a smaller thumbnail) into ‘/static/avatars/’ and updates their Avatar_Filename field in the user table.  All I had to do was to grant the user account that IIS runs under the appropriate write permissions for that dir. Simple enough, and it’s worked for ages.

So now we want to use a web cluster we have a problem. If you’re on Server A and you add an avatar, anyone on Server B won’t see it. We need to have shared file storage.

“I know, I’ll just create another website on an IIS server and that can be ‘static.mydomain.com’ and I’ll just save the files to that across the network, and then reference the different hostname… easy, and I’ll be done in time for lunch”.

HAH! Not so. You can’t save files across to a different machine with IIS. IIS has no network access. Well.. you *can* bodge it, but you have to change the user account that IIS runs on to a domain account, then grant it write access. Not only did that sound dangerous security wise, it also sounded a bit……….. shaky. What if I rebuild the server and forget that bit?

A bit of brain storming later and I had a solution. A solution so cunning, that it needed a super accurate diagram to even think of it:

 

So, take the file the user uploads on the web host, resize it, shred it into a byte array and whack it into a SQL blob on the main server. Then call a webservice on the static file server that says “I have a blob in SQL waiting for you with the file name of XYZ, make a file from it!”

The webservice then grabs the blob from SQL using the filename passed to it in the service call, gets the bytearray, saves it with an IO stream and returns True.

Yes, I could pass the byte array directly to the webservice but it’s not worth it.

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One comment

  1. Pingback: viewmessages.com Architecture « Code, Life and Learning

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