How to deploy an ASP.NET Application with zero downtime

Recursieve_23393 0
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To deploy a new version of our website we do the following:

  1. Zip up the new code, and upload it to the server.
  2. On the live server, delete all the live code from the IIS website directory.
  3. Extract the new code zipfile into the now empty IIS directory

This process is all scripted, and happens quite quickly, but there can still be a 10-20 second downtime when the old files are being deleted, and the new files being deployed.

Any suggestions on a 0 second downtime method?

redundancy deployment iis asp.net
12 Answers

You need 2 servers and a load balancer. Here's in steps:

  1. Turn all traffic on Server 2
  2. Deploy on Server 1
  3. Test Server 1
  4. Turn all traffic on Server 1
  5. Deploy on Server 2
  6. Test Server 2
  7. Turn traffic on both servers

Thing is, even in this case you will still have application restarts and loss of sessions if you are using "sticky sessions". If you have database sessions or a state server, then everything should be fine.

Sklivvz_70280

The Microsoft Web Deployment Tool supports this to some degree:

Enables Windows Transactional File System (TxF) support. When TxF support is enabled, file operations are atomic; that is, they either succeed or fail completely. This ensures data integrity and prevents data or files from existing in a "half-way" or corrupted state. In MS Deploy, TxF is disabled by default.

It seems the transaction is for the entire sync. Also, TxF is a feature of Windows Server 2008, so this transaction feature will not work with earlier versions.

I believe it's possible to modify your script for 0-downtime using folders as versions and the IIS metabase:

  • for an existing path/url:
  • Copy new (or modified) website to server under
    • \web\app\v2.1\
  • Modify IIS metabase to change the website path
    • from \web\app\2.0\
    • to \web\app\v2.1\

This method offers the following benefits:

  • In the event new version has a problem, you can easily rollback to v2.0
  • To deploy to multiple physical or virtual servers, you could use your script for file deployment. Once all servers have the new version, you can simultaneously change all servers' metabases using the Microsoft Web Deployment Tool.
GT_58690

The only zero downtime methods I can think of involve hosting on at least 2 servers.

Sam_Meldrum_160050

A workaround with no down time and I am regularly using is:

  1. Rename running .NET core application dll to filename.dll.backup

  2. Upload the new .dll (web application is available and serving the requests while file is being uploaded)

  3. Once upload is complete recycle the Application Pool. Either Requires RDP Access to server or function to recycle application pool in your hosting control panel.

IIS overlaps the app pool when recycling so there usually isn’t any downtime during a recycle. So requests still come in without every knowing the app pool has been recycled and the requests are served seamlessly with no downtime.

I am still searching for more better method than this..!! :)

user_96598850

I would suggest keeping the old files there and simply overwriting them. That way the downtime is limited to single-file overwrite times and there is only ever one file missing at a time.

Not sure this helps in a "web application" though (i think you are saying that's what you're using), which is why we always use "web sites". Also with "web sites" deploying doesn't restart your site and drop all the user sessions.

user_236160
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