When building WordPress for high traffic website, we maintain and restart the web server frequently for better SEO and better user experience; but we don’t want to interrupt user’s visiting.
When we get familiar with SEO, the link/site structure may change and need to update nginx configuration which need restart of nginx. When nginx new version released for fixing a dangerous security issue, we need upgrade nginx.
So we need at least 2 nginx instance for load balance, and another nginx as proxy server. Let’s build the 3 nginx instance on a single server with the same nginx installation(or use 2 nginx installation if need upgrading nginx ). Two of the instance serves WordPress with the same WordPress installation and the same database.