问题
Currently after a build/deployment of our app (58 projects, large asp.net MVC 3 front end) takes ~15-20secs to load as it goes through the whole 'recycling the app pool' (release configuration).
We do have a web farm if that alters people's answers, but the question really is:
What are people doing in large scale applications where a maintenance window isn't viable (we're a 24/7 very active website) to minimize that initial 'first hit' on the app pool recycle after a deploy?
We've used a number of tools to analyze that startup time and there doesn't really seem to be any way to bring it down so what I'm looking for are what techniques do people employ in order to minimize the impact of a large application deploy affecting users.
回答1:
By default - if you change 15 files in an ASP.NET application at once (even via FTP) then the app pool is automatically recycled. You can change the number of files but as soon as web.config and bin files are changed then it needs to recycle. So in my opinion the ideal solution for an environment like yours would be as follows:
4 web servers (this is an arbitrary number) each server has a status.aspx that the load balancer looks at - use TeamCity to take 2 of these servers "off line" (off the load balancer) and wait 20 seconds for the traffic to filter across. A distributed cache will help keep user experience problems
Use TeamCity to deploy to those 2 servers - run your automated tests etc. and once you are happy put those back into the farm and take the other 2 offline and deploy to those
This can all be scripted / automated. The only issue with this is any schema changes that are not backwards compatible may not allow running the new version site in parallel with old version of the site for the 20 seconds for the load balancer to kick back in
This is good old fashioned Canary Releasing - there are some patterns here http://continuousdelivery.com/patterns/ to help take into consideration. Id also suggest a copy of that continuous delivery book - its like a continuous delivery bible and has got me out of a few situations :)
回答2:
At the very base you could run a tinyget script against the application after completion of deployment which will "warm up" the application however if a customer hits your site before the script can run, they will still face a delay. What do you currently have in place, what post deployment steps do you have in place?
In a farm environment you could stage deployments too, so take one server out of load balance, update it and then bring that online after deployment and take the other out, complete the deployment and then reintroduce into the farm. How is your SQL Server setup - clustered?
回答3:
copy and paste from my post here
We operate a Blue/Green deployment strategy on a 4 tier architecture which has a web site over 4 servers at the top tier. Due to the complexity the architecture introduced for deployments, we needed a way to deploy without disturbing any traffic to the "live" site. Following Fowler's advice, but not quite in the same way, we came up with a solution that means we have 2 sites on each server (a blue and a green, or in our case site A and site B). The live site has the appropriate host header, and once we have deployed and tested to the non-live site, we then flip the headers of the 2 sites so that what was once live is now the non-live site, and vice-versa. The effect is, a robust deployment that can be done in business hours and with the highest level of confidence.
This of course complicates your configuration and deployment slightly, but it's worth the effort. I guess it kind of goes without saying that you want to script both the deployment, and the host header swapping.
回答4:
Firstly, unless you're running Google or something bigger, does a 15-20s load time at 3am for a handful of users really impact that much? I'd say the effort invested in eliminating the occasional lag would far outweigh the 15-20s inconvenience of a couple of users.
I consider it a necessary evil of using ASP.NET unfortunately. Using a pre-compiled site (.DLLs instead of the code-behind files) will lessen the time but not necessarily eliminate it.
The best thing you can do is use something like a status notification bar to warn users they may experience some "issues" during "essential maintenance".
But even then, I'd say in terms of user experience it'd be better to keep quiet and have a handful of people blame their "slow internet" when your site takes 20s to load on one occasion, than announce to all and sundry that it will be slow.
回答5:
You can also try this approach : http://weblogs.asp.net/scottgu/archive/2009/09/15/auto-start-asp-net-applications-vs-2010-and-net-4-0-series.aspx
回答6:
without knowing anything about your site, my first thought is that you might be able to break it down into smaller sites so that they start faster individually.
second, with your web farm, i assume you have some sort of load balancing device in front of that from which you can pull machines out of the pool when they are being deployed. don't put them back in the pool until after you have sent a request against the site to get it started up. you should be able to script this such that you are pretty much clicking a button that takes a machine out, deploys to it, and sends a request after it's back up and happy.
回答7:
You can consider using aspnet_compiler.exe to precompile your application, because I think the delay after deployment is caused by the compilation phase rather than "whole recycling the app pool".
来源：https://stackoverflow.com/questions/8151860/how-are-people-solving-app-pool-recycle-issues-on-deployment-with-large-apps