I was planning on using a new domain name when migrating my legacy site to Drupal. I already have the php script that will translate old urls into Drupal Urls (I'm not using pathauto for that).
Now there is a chance I have to keep showing content on the old domain (mainly for SEO purposes). This site won't have any login or write-backs at all, it basically just shows the content and link to the new site.
How would I intercept the 404's that Drupal would now generate, preferably at a very low bootstrap level since there could be tons of invalid requests?
Update:
Sounds like I could use hook_boot() to intercept every page request early and then have the query string parsed and redirected to the matching node/... page on the same site.
Or, similar to Fast404 I could add an include_once to settings.php and do the redirect there:
include_once('.sites/default/modules/myredirect_module/myredirect_module.inc');
Will there be a big difference between those two options?