IIS 8 publish ASP.NET core application - file in use

Question

Is it possible to publish an ASP.NET (core) application to a running site on IIS 8 without having to stop and start the website manually?

Visual Studio 2015 keeps giving the error that a file is in use. I'm using publish to the file system, because my Web Deploy to a server in our network fails at the end with an error that it cannot authenticate on the server with port 443.

I don't mind IIS having to recycle the application pool, but when I constantly have to put the app down, publish (which takes about a minute) and restart it, it's not really good for the users.

Another option would be something like 2 websites running the same application, but only if this is automatable. Then it would put down 1 of the 2, update this, put it on, put down the second, update this and start it.

A third option is something like a hot update, where I could just update the application while it being on.

Can anyone point me in the right direction (perhaps some blog posts), because my Google searches didn't give me any good information?

Answer 1

If you copy a file called app_offline.htm to the application folder IIS will gracefully stop your application and start serving the contents of the app_offline.htm file. When application is stopped you can copy your files. After files are copied remove the app_offline.htm file and IIS will start your app. VS does that for you when you deploy to Azure but not when deploying to file system.

Answer 2

You mention "two websites running the same application". Do you mean two web servers hosting the same app?

If you already have multiple web servers (aka cluster of servers, or web farm), you can simply take some servers out of the cluster and update them. That is how we push out our updates. We use software from Citrix for managing the server farm. It also handles load balancing. This type of software allows one to monitor the servers, so you can determine when all the users have "moved" off the web servers (that were recently taken out of cluster). Then you can iisreset, deploy the new build, and move on to the next server (or set of servers, depending on your configuration). We have more than 20 virtual web servers. Typically we take down half of the servers, update them, and take the other half down as we put the first half back in the cluster/farm. This should allow for uninterrupted service. I understand you want to automate the process. I'll assume you're using Windows NLB (network load balancing). You could write a PowerShell script to automate taking down the servers. Here's a reference: https://technet.microsoft.com/en-us/library/ee817138

I understand this may be viewed as a workaround. I'm not sure if recycling the app pool is always necessary with ASP.NET Core. I wasn't able to find a definitive answer. Most production applications should be on more than one web server anyway. Even if you don't have a lot of users, you should have multiple web servers for failover purposes.