Optimizing Google Analytics Cookies at Illinois

Introduction

Google Analytics 4 and Google Tag Manager

• Google Analytics 4
  • Google's latest version of their web analytics service, replaces Universal Analytics (UA).
  • Within the GA4 platform, there are 'Accounts' which contain 'Properties' which contain 'Data Streams'
    • Typically only one Data Stream is used within a property when used for a website.
    • Creating a Data Stream generates an associated 'Google Tag'. The tag created for a web Data Stream will have two tag IDs: a 'Measurement ID' (e.g. G-5WMFPCS43H) and a 'Tag ID' (e.g. GT-WK5N5G5J).
    • Other Google services can also use Google tags, but GA4 seems to be the most common on our campus.
• Google Tag Manager
  • Google's tag management system that can be used to manage various tags, including GA4 tags.
  • Not required to use for GA4, but can provide more options for managing tags and tracking.

Google Analytics 4 Cookies

Cookie Accumulation and Browser Errors

Who Can This Affect?

Possible Solutions

• Short-Term
  • Clear the user's browser cookies (End User can implement)
    • Can help fix issues for an individual user
  • Increase the maximum allowable size of request headers on the web server (IT Pro can implement)
    • Can help prevent issues on individual sites
  • Implement a cookie clean up script on your website (IT Pro can implement)
    • Can help prevent issues for groups of users
• Long-Term
  • Setting the GA cookie domain to the relevant subdomain
    • Using Google Tag Manager configuration (GTM User can implement)
    • Using gtag.js configuration (IT Pro can implement)

Solution: Clearing Browser Cookies

Solution: Increasing Max Request Header Size

• IT Pros that have access to a site's web server configuration (Apache, Nginx, IIS, etc.) may be able to increase the maximum allowable size of request headers. Note, this will only help prevent user errors for a specific site.
  • Apache, for example, has the LimitRequestFieldSize directive.
• Should be used cautiously — allowing larger request headers to be sent to the server could potentially be abused by bad actors.
• This is likely not an option for vended services that use an illinois.edu subdomain, unless the vendor is willing to make this change.

Solution: Cookie Clean Up Script

• It is possible to automatically clear _ga_ cookies using JavaScript. Permissions are such that a subdomain site can modify cookies set at the higher level ".illinois.edu" domain.
• A script has been made available on GitHub: https://github.com/UIUCLibrary/ga-cookie-script. By default, the script will clear a user's _ga_ cookies if there are more than 30 accumulated. A higher threshold can be set by passing a max parameter to the script, example below:
  • <script src="https://cdn.jsdelivr.net/gh/UIUCLibrary/ga-cookie-script@1.0.1/ga-cookie-script.min.js?max=40"></script>
• This can be effective when implemented on high traffic pages to 'catch' the most amount of users. For users currently experiencing 400 errors, you could try directing them to a page running the script.
• Shout out to the campus web community for suggesting a script like this as a possibility.

Solution: Setting the Cookie Domain

• The previous solutions have some downsides and are best used as a short-term fix. Clearing cookies is often inconvenient and even if done automatically, is not ideal.
• Sites using GA4 have the ability to set the domain for its _ga_ cookie to the site's own subdomain. This would prevent the cookie from being included in requests to other subdomains.
  • We'll go over some different ways of explictly setting the cookie's domain, depending on how the analytics were set up.
  • Technically, this could temporarily makes things worse since this will generate a new cookie with the relevant subdomain, but the original cookie may not expire for some time.

Solution: Setting the Cookie Domain (GTM config)

Solution: Setting the Cookie Domain (gtag config)

• If you are using Google Analytics without Google Tag Manager, configuration can be added to the existing JavaScript snippet:
  • gtag('config', 'TAG_ID', {'cookie_domain': 'example.illinois.edu'});
• If you don't have access to edit the JavaScript snippet, you could consider using Google Tag Manager to manage the GA4 tag. Steps to add an existing GA4 tag to GTM can be found on the Set up Google Analytics in Tag Manager support page. After adding the GA4 tag to GTM and adding the cookie domain configuration as described in the previous slide, you can switch the site to use the GTM snippets instead of the gtag.js snippet.
• In all cases, after making changes, it is recommended to check that the cookie is being set correctly in the browser's developer tools and that analytics data is being collected as expected.

Questions?