https://using-redux.gatsbyjs.org/
Gatsby example site that shows use of redux.
To use redux in a Gatsby site you'll need to hook in to two of Gatsby's extension points.
Once in replaceRenderer which runs during Gatsby's server rendering process,
and once in replaceRouterComponent which is part of Gatsby's browser APIs.
Check out ./gatsby-ssr.js and
./gatsby-browser.js to see how this is implemented in
this example.