[ci skip] Update changelog, version & upgrade instructions

1 files changed, 42 insertions, 1 deletions

diff --git a/user_guide_src/source/installation/upgrade_303.rst b/user_guide_src/source/installation/upgrade_303.rst
index a98eed0d4..d13a0fe46 100644
--- a/user_guide_src/source/installation/upgrade_303.rst
+++ b/user_guide_src/source/installation/upgrade_303.rst
@@ -11,4 +11,45 @@ Step 1: Update your CodeIgniter files
 Replace all files and directories in your *system/* directory.
 
 .. note:: If you have any custom developed files in these directories,
-	please make copies of them first.
\ No newline at end of file
+	please make copies of them first.
+
+Step 2: Make sure your 'base_url' config value is not empty
+===========================================================
+
+When ``$config['base_url']`` is not set, CodeIgniter tries to automatically
+detect what your website's base URL is. This is done purely for convenience
+when you are starting development of a new application.
+
+Auto-detection is never reliable and also has security implications, which
+is why you should **always** have it manually configured!
+
+One of the changes in CodeIgniter 3.0.3 is how this auto-detection works,
+and more specifically it now falls back to the server's IP address instead
+of the hostname requested by the client. Therefore, if you've ever relied
+on auto-detection, it will change how your website works now.
+
+In case you need to allow e.g. multiple domains, or both http:// and
+https:// prefixes to be dynamically used depending on the request,
+remember that *application/config/config.php* is still a PHP script, in
+which you can create this logic with a few lines of code. For example::
+
+	$allowed_domains = array('domain1.tld', 'domain2.tld');
+	$default_domain  = 'domain1.tld';
+
+	if (in_array($_SERVER['HTTP_HOST'], $allowed_domains, TRUE))
+	{
+		$domain = $_SERVER['HTTP_HOST'];
+	}
+	else
+	{
+		$domain = $default_domain;
+	}
+
+	if ( ! empty($_SERVER['HTTPS']))
+	{
+		$config['base_url'] = 'https://'.$domain;
+	}
+	else
+	{
+		$config['base_url'] = 'http://'.$domain;
+	}