A decision with consequences.
THE OPTIONS
yourdomain.com/blog blog.yourdomain.com
WHAT SEARCH ENGINES DO
A subdirectory is treated as part of the same site, sharing its authority.
A subdomain is treated more separately.
FOR CONTENT THAT BELONGS TO YOUR SITE
A subdirectory. A blog, a knowledgebase, a resources section.
FOR GENUINELY SEPARATE THINGS
A subdomain. A different application, a staging copy, a customer portal.
THE TECHNICAL CONSIDERATION
A subdirectory shares the main site's .htaccess and cookies.
Two applications in the same domain can conflict through rewrite rules.
A subdomain avoids that.
THE PRACTICAL ADVICE
If the content supports your main site's purpose, use a subdirectory.
If it is a separate system, use a subdomain.
CHANGING LATER
Possible, and it requires redirecting every URL.
Decide deliberately at the start.
