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Legion Infrastructure


today I want to provide some information on how the new Infrastructure looks like. The main goal of this topic is to help new Legion modders understand how things work now. The following information only show the basics of this topic, but will cover everything you need to get you started. 

Please note that this is a complex topic. If you find any errors please let me know so I can fix them.


This Image shows every part of the new Infrastruture you need to know right now. We will now talk about every part in Detail.

1. CDN
The word CDN is often used as a false name for TACT. A CDN is the combination of TACT and webserver. Since webservers are not a Blizzard thing they are not covered here. The only thing you need to know is that for Legion a simple http based webserver is enough to host your TACT. This has changed in BFA. A CDN serves as a provider for the client to patch itself. Having a complete CDN will allow your client to complete itself by just having a WoW.exe.

The TACT-Files are a lage amount of files that basically replaced the MPQ files we knew. Its a modern storage that holds ALL FILES OF EVERY LOCALIZATION. You can not only have TACT files of one localization. This is also the place where you will add custom files. Keep in mind that most files within a TACT uses FileDataIDs by now.

3. Client ant CASC
Once you connect your client to a CDN it will start downloading files for its selected configuation (e.g OS, localization,...). These files are stored in a CASC. You cannot build a TACT from a CASC. You could theoratically copy these CASC-files to another client to "patch" it but this would be a very bad way of doing things.

4. Trivia

  • Your best bet for starting Legion modding is to setup your own CDN. This way you can always download a fresh client.
  • You cannot / should not add files to your client anymore like you did in early versions of Legion modding
  • You can modify your TACT using Caschost or TACTAdder
  • Better make a Backup of your TACT files those are valuable
  • You can download the most recent TACt files from blizzard using BuildBackup
  • Older versions of TACT are not available anymore. (But some modders do still have them around)
  • FileDataIDs usually dont change between patches and even expansions

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