gatsby-node.js

const path = require(`path`)

const { fmImagesToRelative } = require("gatsby-remark-relative-images")

exports.onCreateNode = ({ node }) => {
  fmImagesToRelative(node)
}

exports.createPages = ({ actions, graphql }) => {
  const { createPage } = actions

  const postTemplate = path.resolve(`src/templates/postsTemplate.js`)

  return graphql(`
    {
      allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] }
        limit: 1000
      ) {
        edges {
          node {
            excerpt(pruneLength: 250)
            html
            id
            frontmatter {
              date
              path
              title
              description
              showOnFrontPage
            }
          }
        }
      }
    }
  `).then(result => {
    if (result.errors) {
      return Promise.reject(result.errors)
    }

    return result.data.allMarkdownRemark.edges.forEach(({ node }) => {
      createPage({
        path: node.frontmatter.path,
        component: postTemplate,
        context: {}, // additional data can be passed via context
      })
    })
  })
}