Configuring Google Analytics with Gatsby is straightforward.

Gatsby Google Analytics Plugin

Using the plugin gatsby-plugin-google-analytics, add to gatsby-config.js

{
    resolve: `gatsby-plugin-google-analytics`,
    options: {
        trackingId: `UA-102737102-1`,
        head: false,
        exclude: [`/private/**`],
        cookieDomain: `${domain}`,
    },
},

where domain = johnvincent.io

This plugin is only executed for production builds.