如何更新网站而不使其崩溃？

Question

I need the best practice for updating one or more files on my website without making it go down;

example, if i update Model.php file, the upload will take few seconds, like one or two seconds before it replaces the file on the server, in the meantime, the website will show some error that model.php is not found, or not complete, even if i suppress the errors, the website will die eventually.

what is the best practice for that?

Answer 1

One practice I've often used and seen in practice is -

• use a Version Control System (VCS) like SVN or Git

• on the live server, make the site's web root a symbolic link to a directory containing the latest revision of your web site (eg. /www/domain.com/r555 ) for revision no. 555

• when a change comes up, check in changes to the VCS

• have a script that checks out the latest revision to a new directory, carrying the revision name (say, /www/domain.com/r556 )

• when the checkout is done, change the symbolic link and make it point to /www/domain.com/r556 .

There are a few snags if you have dynamic data like file uploads and such that you can't have in the VCS, but they can all be dealt with without downtime.

Things like database changes may still require some kind of maintenance mode, though.

Answer 2

When your updating production, create a folder called 1.1 and put the new application in there (whether manually or through some VCS) then symlink the public html directory to it. The switch will be instantaneous.

This is not an uncommon approach as one of the benefits is if there's something wrong with the code, the admin can immediately symlink back to the 1.0 folder.

Another good thing is to name the VCS tag the same as folder so the version in use can be easily tracked.

Answer 3

Use a caching server/application to keep a cached copy available for users. Varnish is an example. You can set Varnish to cache contents for a set amount of time, and an alternative amount of time in case the actual website's server is not accessible ( Model.php not found errors and similar).

In this case if you update your production system, Varnish can keep on serving a cached copy of the website until the backend is up and running properly again (be it 2 seconds or 2 hours). Just remember to purge the Varnish cache after updates in case something (UI, content, etc.) changes for the users.

All web servers have some caching features available, but Varnish and the like are made for caching.

Another option is to run two or more instances of the same website behind a load balancer like HAProxy . Update one at a time and HAProxy can redirect traffic to the one that you are not currently updating.

Head over to Server Fault in case you need more information on server level caching or load balancing.