ServerSide Google Tag Manager Proxy in PHP

Goal

• Place this proxy script on your webserver to be able to use your website's main domain as server_container_url in GTM.
• You can also use your website's domain as 'Server container URLs' on the Container Settings so you can preview requests without cross-domain cookie problems.

This is best practice according to Google.

graph TD
    Browser@{ shape: "stadium", label: "Visitor's Browser" }

    subgraph AppServer [https\://www\.yourdomain\.com]
        direction TB
        Website_Content@{shape: "document", label: Website Content}
        SsGtmProxy[ss-gtm-proxy]
    end

    Browser -- request --> Website_Content;
    Website_Content -- HTML --> Browser;
    Browser -- GTM requests
     /g/*
     /gtag/*
     /gtm/*
     --> SsGtmProxy;
    SsGtmProxy -- forwards request --> Https_Proxy;

    subgraph GtmServer [https\://gtm.anydomain.com/prefix]
        Https_Proxy[HTTPS Proxy]
        direction TB
        Https_Proxy -- /prefix/g/* 
             /prefix/gtag/* --> GtmServerContainer[GTM Server Container];
        Https_Proxy -- /prefix/gtm/* --> GtmPreviewContainer[GTM Preview Container];
    end

    %% Style definition for highlighting
	style SsGtmProxy stroke-width:4px

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Requirements

• PHP 7.4 or greater
• Composer 2.x
• Apache 2.4 or greater

If you are not running Apache, you will need to manually implement the contents of the .htaccess in your webserver.

Installation

0. Prerequisites

• You need to run the 2 GTM Docker containers on your own server
  • one for the GTM Server
  • one for the GTM Preview Server
• These Docker containers should have a public available HTTPS proxy (Caddy/HAProxy/Nginx) in front, with a public available URL with a working certificate.
  • In the examples we use https://gtm-docker-server.domain.com/prefix as the URL of this proxy.
• URL mappings in the container proxy server should be like this:

Incomming URL	Edit Path	Pass to Container	Container Port
/prefix/gtm/*	Strip /prefix	GTM Preview Server	8080
/prefix/g/*	Strip /prefix	GTM Server	8080
/prefix/g/gtm.js	Strip /prefix/g	GTM Server	8080
/prefix/g/ns.html	Strip /prefix/g	GTM Server	8080
/prefix/gtag/*	Strip /prefix	GTM Server	8080
/prefix/*	Strip /prefix	GTM Server	8080

• Test the installation:

  • https://gtm-docker-server.domain.com/prefix/gtm/healthy
  • https://gtm-docker-server.domain.com/prefix/g/healthy
  • https://gtm-docker-server.domain.com/prefix/gtag/healthy

• These URLs will return a 400 error until you complete step 6

  • https://gtm-docker-server.domain.com/prefix/g/gtm.js
  • https://gtm-docker-server.domain.com/prefix/g/ns.html
  • these URLs also need the correct ?id=GTM-[WEBCONTAINER] parameter to work

1. Install

Clone this repository, and execute the installation steps:

cd ~/httpdocs
git clone https://github.com/deovero/ss-gtm-proxy gtm
ln -sn gtm g
ln -sn gtm gtag
ln -sn gtm _
cd gtm
cp config.example.php config.php
composer install

2. Update config.php

• Update ~/httpdocs/gtm/config.php with the paths to your GTM server, for example https://gtm-docker-server.domain.com/prefix

3. Verify

• Visit https://yourwebsite.com/gtm/healthy, this should also show ok
• Visit https://yourwebsite.com/g/healthy, this should show ok
• Visit https://yourwebsite.com/gtag/healthy, this should show ok

4. Configure GTM

I assume you already know how Server Side GTM works.

• On your GTM Server Container go to 'Admin' in the top menu, then to 'Container Settings'
  • In the 'Server container URLs' field add your website URL, for example https://yourwebsite.com as the only item
  • Submit/Publish the Server Container
  • Wait a couple of minutes for the changes to be applied by the Docker container
• On your GTM Web Container a Tag of type 'Google Tag' must exist, containing your Analytics Tag ID
  • On this Tag set the configuration parameter server_container_url to your website URL, for example https://yourwebsite.com
  • This tag should have a trigger on 'Initialisation - All Pages'
  • Submit/Publish the Web Container, or use Preview Mode

5. Test

• If you open PREVIEW on the GTM Server Container, leave this tab open
• Visit your website in the same browser on another tab, you should see the request on the preview page.
• Check your Google Analytics Realtime report to see if the hits are coming in.

6. Serve GTM JavaScript from your own domain

To prevent any cross domain traffic you can serve the GTM JavaScript from your own domain.

• On your GTM Server Container add the 'Google Tag Manager: Web Container' Client
  • Allow to serve gtm.js for the ID of your GTM Web Container
• On your GTM Server Container edit the GT4 Client
  • Enable 'Default gtag.js paths for specific IDs'
  • Fill in the measurement ID of your Analytics, this looks like G-XXXXXXXXXX
• On these two settings only enable Region Specific settings if either:
  • Your website is behind one of the proxies that provide region information like Cloudflare.
  • You have manually provided the geo location headers
• Publish the Server Container
• Wait a couple of minutes for the changes to be applied by the Docker container
• Press the [Preview] button on the GTM Server Container management page
• Test the installation: https://gtm-docker-server.domain.com/prefix/gtm.js?id=GTM-[WEBCONTAINER] this should display the GTM JavaScript. If you are using Region Specific settings, this may fail if the gtm-docker-server.domain.com is not passing GeoIP information. You should be able see the request on the Preview page.
• Test the proxy: https://yourwebsite.com/g/gtm.js?id=GTM-[WEBCONTAINER]
• On your website source code where GTM is loaded, you should replace:
  • https://www.googletagmanager.com/gtm.js by https://yourwebsite.com/g/gtm.js
  • https://www.googletagmanager.com/ns.html by https://yourwebsite.com/g/ns.html
• Test your website
• Test if the tags added to the GTM Server Container work, like Google Analytics using the Realtime overview
  • To use GT4 tracking server-side, you need to add the 'Google Analytics GA4' tag on the Server Container with a trigger on All Pages

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• Created by DeoVero BV / Jeroen Vermeulen
• Thanks to @jenssegers for his work on PHP Proxy script which does the heavy lifting.