How much effort is it to migrate from other competitive application servers to GlassFish?

Effort estimates are difficult to predict without understanding application details and existing and proposed infrastructure. We recommend that your first identify proprietary code you may be using specific to your existing application server. The simplest way to do this is to GlassFish verifier tool which is bundled with the GlassFish v2 distribution in the <b>gf-install/bin</b> directory. Run the verifier as follows:
<p>
verifier.sh --portability <achive-file>
<p>
verifier.bat --portability <archive-file> (On Windows)

<p>Other ways to identify the proprietary code include
<ul>
<li> Java EE Application Verification Kit (AVK), which is freely available avk </li>
<li> GlassFish Admin Console. </li>
<li> NetBeans Packaged Archive project </li>
</ul>

<p>See <a href="http://weblogs.java.net/blog/sekhar/archive/2008/09/_when_migrating_1.html">Verification Tools for Migration to GlassFish</a> for more details on what each tool has to offer.