Magento – How to Disable Cache in Custom Widget

First of all you need to keep in mind that when you are in FPC cached page, the block is not getting created via layout. So first time when FPC page gets popuplated getChildHtml() returns you a correct block, but second time, it will not instantiate it, since Layout XML is not applied at all on cached response.

Any block you are referring to within FPC scope, should be created manually without using layout xml, so you can re-use it even, when layout is not available.

As far as I know, banners already FPC compatible, you should take a look into: Enterprise_PageCache_Model_Container_Banner

You have already found your solution. You are just a few steps off. The answer is indeed the same as: https://stackoverflow.com/questions/8405232/disable-bypass-magento-full-page-cache-on-single-page.

You need to see if the action is an instance of the CMS controller. Then you need to check to see if the page being requested is the one you want to not cache.

1-create the module

2- insert xml in config.xml

3- insert the function in your observer

public function processPreDispatch(Varien_Event_Observer $observer)
{
    $action = $observer->getEvent()->getControllerAction();

    // Check to see if $action is a Product controller
    if ($action instanceof Mage_Cms_PageController) {

        $cache = Mage::app()->getCacheInstance();

        // Tell Magento to 'ban' the use of FPC for this request
        $cache->banUse('full_page');
    }
}