Existing web analytics client side implementations through standard Google Tag Manager containers rely on a browser based tagging solution to add tags to the website and send data to third party platforms. This has historically worked great for sending data to ad serving platforms, but with the addition of Apple’s ITP and browser limitations on third party data collection there are now downsides to client side tagging.
For example, if a user visits your website from an Apple device then the cookie placed on their browser by Facebook, Google, and others to identify to identify them will be deleted within 24 hours. This means that if I come back to the site the next day your third party platforms will view you as a different user. This is why you oftentimes see Google Analytics “New User” percentages well above 90%.
Server side tagging is what will enable marketers and analytics teams to implement future state tracking capabilities like the Facebook conversions api (CAPI).
Client Side Tagging
Client side tagging solutions like traditional GTM containers place tags that send data to third party platforms on the website. All of the data collection in this context happens on the “client-side” (within the browser). This means that the cookies that are placed by your third party platforms like Facebook are viewed as third party cookies. In this context Facebook places a cookie which has a source of facebook.com which does not match your domain and is therefore 3rd party.
This also means that your data collection is victim to users who block on site scripting via adblock or disabled javascript and errors with data payloads. For example, ~15% of all ecommerce purchases are missed within Google Analytics due to some combination of possible errors with client side tagging.
Server Side Tagging
Server Side Tagging solves for these problems by sending data through a tagging server hosted on your domain (think analytics.yourdomain.com). Data from cookies placed by third parties like Facebook can be read from the browser by your tagging server and then stored in a 1st party context (where the domain on the tagging server matches the domain of your website). This means that data for a single user can be stored on the tagging server far beyond the 24 hours that cookies last when using an Apple device or browser that limits cookies.
The use of server side tagging also allows for the connection of other third party data streams that can solve for missing data. For example, you can connect your tagging server via Google Tag Managers Server Side container to services like Shopify’s Webhook. This means that transactional data is delivered directly from Shopify’s APIs to your tagging server resulting in no loss of conversion data. You can immediately begin collecting the 15% of orders that were being lost in your client side tagging setup.
Downsides to Server Side Tagging
There are a few downsides to server side tagging setups in their current state. Tools like Google Tag Manager’s Server Side container are still in beta and do not have support for connections to many third party services. That means that if you want to deploy a server side container today you will need to develop your own connections to your third party platforms or rely solely on the data from your existing client side container.
One of the other downsides to server side containers is that because they are hosted on a subdomain of your existing website there are hosting and data transfer costs associated with them. I have personally hosted tagging servers within Google Cloud Platform and the costs to do so is often marginal, but there is additional IT support and the cost is greater than the free client side data transfers.
The Future of Tagging
When they deployed the server side option for Google Tag Manager Google indicated that they believe there is a future for tagging in a server side environment. The use of server side tagging solves for many of the pain points of client side tagging. As with all new technologies there is a learning curve to deploying server side tagging which will no doubt decrease as GTM’s server side container comes out of beta and begins to support integrations with other third party platforms.
For more information on server side tagging via Google Tag Manager take a look at these resources:
Provisioning Server:
https://developers.google.com/tag-platform/tag-manager/server-side
Sending Data to Tagging Server:
https://developers.google.com/tag-platform/tag-manager/server-side/send-data
Building a Server Tag:
https://developers.google.com/tag-platform/tag-manager/server-side/how-to-build-a-server-tag
Server Side Tagging Overview from the king himself Simo Ahava:
https://www.simoahava.com/analytics/server-side-tagging-google-tag-manager/