While working on a Symfony2 application which uses locale prefixing of URLs to support a multilingual site, I wanted to redirect the root URL (http://mysite.com/) to that of my default locale (http://mysite.com/en/).
This can be done quite simply with routing configuration, which I learned from this cookbook article. Using the standard container parameter 'locale', which sets a default locale, we can also embed the locale value dynamically:
root: pattern: / defaults: _controller: FrameworkBundle:Redirect:urlRedirect path: /%locale%/ permanent: true
Adding the above to my app/config/routing.yml file was all I needed to make /en/ the default path of my site.