Vue proxy setting does not work
The article likely refers to an outdated method of setting up the proxy. The latest version of @vue/cli (currently 3.0.0-rc.3) has a new method of configuring the dev server.
For an equivalent setup of that proxy, create vue.config.js (if it doesn't exist already) with the following contents:
module.exports = { devServer: { proxy: { '/api': { target: 'http://localhost:9000', ws: true, changeOrigin: true } } }}