Magento 2.2 : How to programatically clear the varnish cache by cache tag

Question

I need to switch the currency based on user IP location so I'm using this auto currency extension, it works only when I disabled the FPC otherwise it just cache the previous content and never gets changed.

I'm looking to programmatically clear the varnish cache by the cache tag of the store currency. I tried the below logic in the observer (controller_action_predispatch) but it does not work.

protected $config;
protected $purgeCache;

public function __construct(
    \Magento\PageCache\Model\Config $config,
    \Magento\CacheInvalidate\Model\PurgeCache $purgeCache
) {
    $this->config = $config;
    $this->purgeCache = $purgeCache;
}

public function execute(\Magento\Framework\Event\Observer $observer)
{
    $tags = [];
    $pattern = "((^|,)%s(,|$))";
    $tags[] = sprintf($pattern, 'store');
    $this->purgeCache->sendPurgeRequest(implode('|', array_unique($tags)));
}

Thanks in advance.

Answer 1

Instead of trying to invalidate cache via Magento which is under the 2 difficult things in CS:

1. Naming things
2. Cache invalidation
3. Off-by one errors :)

Instead leverage Varnish itself with a module which implements the same maxmind GeoIP db within Varnish to set proper HTTP Headers like so:

set req.http.X-Country-Code = geoip.country_code(req.http.X-Forwarded-For);

Full Varnish config example in original sources.

NOTE: Your host setup may need adjusting, and Varnish will need to be recompiled which can be a task in itself with versions specific for the module and Magento.

Source:

• https://magento.stackexchange.com/a/217313/69
• https://rageagainstshell.com/2016/05/geoip-location-in-varnish/

Answer 2

If you need to implement a feature that needs to bypass the FPC in Magento 2, the recommended way is to write a Punch Hole implementation for your requirement.

Magento 2 has a structured way to get this written: I have an example at: https://bitbucket.org/magstaging/punchhole