Server-side Google Tag Manager<\/a> is essentially a server application<\/strong> (running on Docker<\/a>, on the other hand, is an environment for creating, sharing, and running applications, right from the Docker platform itself.<\/p>\n In short, it\u2019s a way to package<\/em> an entire application and its execution environment, so that anyone (or any environment) can deploy a Docker container and instantly get the application up and running.<\/p>\n When you deploy server-side Google Tag Manager<\/a> in Google Cloud Platform (the default, recommended way), for example, what you are actually doing is deploying the application via<\/em> Docker on a Cloud Run instance.<\/p>\n Well, this article shows you how you can deploy server-side Google Tag Manager on your local computer<\/strong>, so that it sends requests and responds to them over <\/p>\n <\/a><\/p>\n Running on Docker Desktop<\/span><\/p>\n<\/div>\n Running on The solution is based on the Read on!<\/p>\n \n \n Subscribe to the Simmer newsletter<\/a> to get the latest news and content from Simo Ahava into your email inbox!\n <\/p>\n <\/span><\/p>\n This article utilizes Docker Desktop<\/a>, a handy user interface for interacting with Docker. It installs all the necessary components automatically.<\/p>\n The Docker Personal<\/strong> plan is free to use and comes with everything you need to run the solution locally. Follow this link<\/a>, download Docker Desktop, and start it up.<\/p>\n If you want to avoid a persistent resource hog, open Docker Desktop settings, and in the General<\/strong> tab, uncheck Start Docker Desktop when you sign in to your computer<\/strong>.<\/p>\n<\/blockquote>\n If you prefer to use a CLI for running Docker, just make sure you have both <\/p>\n <\/a><\/p>\n<\/div>\n You\u2019ll also need to clone the GitHub repository<\/strong>. Browse to the repository<\/a> and clone it to your local machine using whatever method you prefer.<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n Once you have the repository cloned and Docker up and running, we can move on to configuring the deployment and actually running it.<\/p>\n The first thing you\u2019ll need to do is configure some environment variables<\/strong>.<\/p>\n First, in your terminal<\/strong>, copy the You can use whatever editor you\u2019re comfortable with (I\u2019m an Emacs<\/a> guy).<\/p>\n Next, set the container configuration string<\/strong> and the GA4 Measurement ID<\/strong> in the Once you\u2019ve made the changes, save the <\/p>\n <\/a><\/p>\n<\/div>\n Now that you have the environment prepared, it\u2019s time to build the container image<\/strong> and run the stack.<\/p>\n The easiest way to build the image is to open the terminal<\/strong> in Docker Desktop first:<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n The Docker Terminal is just like your own local terminal application, but it comes equipped with all the CLI tools we need to build the container image and run everything.<\/p>\n The cool thing is that you only need to run this step once<\/strong>. After the image is built, you can use the Docker Desktop UI for everything else.<\/p>\n Once the terminal is fired up, browse to the project folder on your local filesystem. There, run the command:<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n When the build steps are complete, you can open the Containers<\/strong> tab in Docker Desktop, and you should see By default, the tagging server<\/strong> runs on A quick check to see if everything works is to open a web browser and browse to both Now that the servers are running, you can enter Preview mode.<\/p>\n In a web browser, browse to your SGTM container and edit Admin<\/strong> -> Container Settings<\/strong>:<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n Save the changes, then go to your GTM Workspace and click the Preview Picker<\/strong> button.<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n Next, choose the <\/p>\n <\/a><\/p>\n<\/div>\n Now you can open a new tab and send a test request, for example by browsing to <\/p>\n <\/a><\/p>\n<\/div>\n Congratulations! You now have server-side Google Tag Manager<\/strong> running locally.<\/p>\n To stop<\/strong> \/ restart<\/strong> the server, all you need to do is go to Docker Desktop, and hit the stop \/ play button next to the <\/p>\n <\/a><\/p>\n<\/div>\n Because the server is running on a port<\/strong> ( This is due to While this does<\/em> work, any event request that follows will fail because it tries to send the request to I\u2019ve reported this as a bug to Google. In the meantime, there is a workaround to use I\u2019ve also suggested to Justus that the nginx<\/strong> reverse proxy could be configured to map a subdomain such as As if building the localhost Google Tag Manager server wasn\u2019t enough, Justus<\/a> wrapped everything in a utility called DataLayer Relay<\/strong> (read the documentation here<\/a>).<\/p>\n Once the Docker container is running, you can check the template website at <\/p>\n <\/a><\/p>\n<\/div>\n The purpose of DataLayer Relay<\/strong> is to automatically collect any and all It\u2019s a solution that relies entirely<\/em> on a well-oiled It uses the <\/p>\n <\/a><\/p>\n<\/div>\n You can click the buttons on the page to see what is pushed to <\/p>\n <\/a><\/p>\n<\/div>\n You can verify the result in server-side Google Tag Manager Preview mode:<\/p>\n <\/p>\n <\/a><\/p>\n<\/div>\n The relay has some neat ideas, such as persistent fields<\/strong>, which lets you configure certain event parameters so that they automatically<\/strong> persist in all Consult the documentation<\/a> to see all the cool things you can do with DataLayer Relay.<\/p>\nNode.js<\/code>), which Google has helpfully composed<\/em> into a Docker image<\/a>.<\/p>\nlocalhost<\/code>.<\/p>\n![\"Running](\"https:\/\/www.simoahava.com\/images\/2025\/11\/docker-desktop.jpg#ZgotmplZ\")
<\/p>\nlocalhost<\/code> has its uses. It lets you test a complete server-side Google Tag Manager deployment without having to worry about where it\u2019s hosted, as it\u2019s running solely on your own computer. It\u2019s a great way to get everything running correctly before moving to a production environment.<\/p>\ndatalayer-relay<\/code><\/a> project developed by my colleague Justus H\u00e4m\u00e4l\u00e4inen<\/a>. While the focus of this article is on getting the server-side tagging environment up and running, we\u2019ll walk through the Data Layer relay technology, too, as it\u2019s a great technical demo of how to optimize data dispatch for server-side Google Tag Manager.<\/p>\n
\n X<\/span><\/p>\n
\n The Simmer Newsletter<\/strong>\n <\/p>\nInstall server-side Google Tag Manager on your local machine<\/h2>\n
What you\u2019ll need<\/h3>\n
\n
docker<\/code> and docker-compose<\/code> up and running. If you follow this route, you should already know how to run containers, so I won\u2019t include a CLI guide in this article (you can always check Justus\u2019 documentation in the repo<\/a>).<\/p>\n![\"Docker](\"https:\/\/www.simoahava.com\/images\/2025\/12\/docker-desktop.jpg#ZgotmplZ\")
<\/p>\n![\"Git](\"https:\/\/www.simoahava.com\/images\/2025\/12\/git-repo.jpg#ZgotmplZ\")
<\/p>\nConfigure the environment<\/h3>\n
.env.example<\/code> file into .env<\/code>:<\/p>\n# Copy the example environment file<\/span>\n$ cp .env.example .env\n\n# Edit with your actual values<\/span>\n$ nano .env<\/code><\/pre>\n<\/div>\n.env<\/code> file.<\/p>\n# Get this from GTM Admin > Container Settings<\/span>\nCONTAINER_CONFIG<\/span>=your_container_config_here\n\n# Your GA4 Measurement ID (e.g., G-ABC123XYZ)<\/span>\nGA4_PROPERTY<\/span>=G-ABC123XYZ<\/code><\/pre>\n<\/div>\n.env<\/code> file. Here\u2019s what my configuration looks like:<\/p>\n![\"The](\"https:\/\/www.simoahava.com\/images\/2025\/12\/env-file.jpg#ZgotmplZ\")
<\/p>\nBuild the image and run the server<\/h3>\n
![\"Docker](\"https:\/\/www.simoahava.com\/images\/2025\/12\/docker-terminal.jpg#ZgotmplZ\")
<\/p>\n![\"docker-compose](\"https:\/\/www.simoahava.com\/images\/2025\/12\/compose-ready.jpg#ZgotmplZ\")
<\/p>\ndatalayer-relay<\/code> running.<\/p>\nhttps:\/\/localhost:8888<\/code> and the preview server on https:\/\/localhost:8889<\/code>. Yes, both are behind SSL.\u00a0The application automatically issues SSL certificates, but as they\u2019re patched for localhost you might need to click through security warnings when you actually visit those URLs.<\/p>\nhttps:\/\/localhost:8888\/healthy<\/code> and https:\/\/localhost:8889\/healthy<\/code>. Both URLs should show the text ok<\/code> as the content.<\/p>\nOpen a preview window<\/h3>\n
![\"Container](\"https:\/\/www.simoahava.com\/images\/2025\/12\/container-settings.jpg#ZgotmplZ\")
<\/p>\n![\"Preview](\"https:\/\/www.simoahava.com\/images\/2025\/12\/change-context.jpg#ZgotmplZ\")
<\/p>\nlocalhost<\/code> URL and then hit Preview. You should see Tag Assistant open in a new tab, with https:\/\/localhost:8888<\/code> as the host. Remember, you might need to click through browser security prompts as the SSL certificate doesn\u2019t have proper authority.<\/p>\n![\"Proceed](\"https:\/\/www.simoahava.com\/images\/2025\/12\/proceed-to-localhost.jpg#ZgotmplZ\")
<\/p>\nhttps:\/\/localhost:8888\/test<\/code>. If all works correctly, you\u2019ll see the test<\/code> path appear in Tag Assistant.<\/p>\n![\"Test](\"https:\/\/www.simoahava.com\/images\/2025\/12\/test-request.jpg#ZgotmplZ\")
<\/p>\ndatalayer-relay<\/code> container stack:<\/p>\n![\"stop](\"https:\/\/www.simoahava.com\/images\/2025\/12\/stop-play-datalayer-relay.jpg#ZgotmplZ\")
<\/p>\nCaveat<\/h3>\n
https:\/\/localhost:8888<\/code>), you won\u2019t be able to use the server_container_url<\/code> setting in your Google Tag Manager tags or in your gtag<\/code> configuration.<\/p>\nserver_container_url<\/code> stripping the port<\/strong> from the host before the event request is sent. Interestingly, you can<\/strong> load the gtag.js<\/code> library with the config command:<\/p>\ngtag('config', 'G-123123123', {server_container_url: 'https:\/\/localhost:8888'})<\/code><\/p>\nhttps:\/\/localhost\/<\/code>.<\/p>\ntransport_url<\/code> instead. It\u2019s outdated tech at this point, and it does mean that not all server-side features are available, but just for event dispatch it works fine.<\/p>\nhttps:\/\/testing.your.website<\/code> to the localhost address, so that you could mock requests to a custom subdomain without having to make any actual DNS changes. This would solve all problems because then you could configure your tags to use https:\/\/testing.your.website<\/code> (or whatever domain you like) as the server_container_url<\/code> endpoint.<\/p>\nHow to use DataLayer Relay<\/h2>\n
http:\/\/localhost:3000<\/code> (That\u2019s http<\/strong>, not https<\/strong>!):<\/p>\n![\"Test](\"https:\/\/www.simoahava.com\/images\/2025\/12\/test-page.jpg#ZgotmplZ\")
<\/p>\ndataLayer<\/code> event objects into server-side GTM, using the GA4 data stream to dispatch them.<\/p>\ndataLayer<\/code> configuration.<\/p>\nGA4_PROPERTY<\/code> and SERVER_CONTAINER_URL<\/code> configuration entries in the .env<\/code> file to build the requests. To generate the data stream, it uses a vanilla gtag.js<\/code> installation, which means that you do not need to load a client-side Google Tag Manager container on the page. The gtag.js<\/code> library is loaded from the server-side Google Tag Manager container, so make sure you edit the GA4 Client<\/strong> to allow library loads from the GA4 ID you added to the configuration.<\/p>\n![\"GA4](\"https:\/\/www.simoahava.com\/images\/2025\/12\/ga4-client.jpg#ZgotmplZ\")
<\/p>\ndataLayer<\/code> and what is ultimately transported to server-side GTM.<\/p>\n![\"Purchase](\"https:\/\/www.simoahava.com\/images\/2025\/12\/purchase-test.jpg#ZgotmplZ\")
<\/p>\n![\"Preview](\"https:\/\/www.simoahava.com\/images\/2025\/12\/preview-mode.jpg#ZgotmplZ\")
<\/p>\ngtag()<\/code> calls that are done during that page load.<\/p>\n