The fastest request is the one you never make

Paul Chin Jr
November 16, 2020

Lightning Storm Photo by NOAA on Unsplash

C.R.E.A.M — Cache rules everything around me

As web developers, we interact directly with the application layer through HTTP. Reducing your application to requests and responses is a useful technique to model your architecture. Your application can have multiple routes in both the front and back end. Keeping some requests local will maximize the performance, but can also introduce other problems when requesting assets from a long-lived cache. We want to cache assets as long as possible to reduce network latencies, but we have to make sure users are receiving the latest version. What we’d like is the fastest delivery of the freshest asset we have.


Creating unique filenames will force the cache to update but managing those file names can be cumbersome. Each asset becomes a new file every time you update it. For example: index.js becomes index-somehash123.js after a saved change. Then it will update again to index-somehas456.js after another saved change. This process hashing a filename is known as fingerprinting.

Let’s start by creating a new Begin app, where we will add an API route that will return the fingerprinted filename of the client-side JavaScript file at runtime!


Take a look at the static assets tab in your Begin console and you will see two files that have been uploaded to S3 that correspond to the /public folder in the project.

Asset Tab

Next, let’s edit app.arc by adding @static fingerprint true which will fingerprint the files and create an asset manifest, public/static.json.

# app.arc
get /
fingerprint true

After you push that change to your default branch, Begin will create a new build. Now take another look at the Static Assets tab. Your app is configured to serve the latest asset from a long-lived cache. Your S3 bucket will have background-fingerprint123.jpg, but your client-side code will still recognize background.jpg, thanks to static.json!

Asset Tab

Now you know that users will always have the freshest content.

Fingerprinting is available on every Begin app with just one line of code in the app.arc file. Begin will keep track of your static assets for you and configure the redirects behind the scenes so your local development experience will still be seamless.

Runtime helpers for static assets

@architect/functions is also updated to include a helper method for calling filenames at runtime inside your Lambda functions. Let’s continue using our example above to see this helper in action. We’re going to inspect the get-index handler that returns the main contents of our page.

// src/http/get-index/index.js
const Main = require('@architect/views/main.js')
const arc = require('@architect/functions')
// Customize your site by changing the data below
exports.handler = async function Index () {
  let body = Main({
     * Basic bio
    fullname: 'Your Name', // ←  Start by adding your name!
    title: 'My personal site!',
    occupation: 'Artist & Photographer',
    location: 'West Glacier, MT',
    bio: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Quis ipsum suspendisse ultrices gravida. Risus commodo viverra maecenas accumsan lacus vel facilisis.',
     * Contact / social
     * - Comment out any item below to remove it from your page
    email: '',
    twitter: 'yourTwitter',
    linkedin: 'your-linkedin-name',
    instagram: 'yourInsta',
    facebook: 'your-facebook-name',
     * Layout
    photographer: 'Ivana Cajina',
    service: 'Unsplash',
    credit: '',
    // Applying arc.static for a runtime lookup of filename from S3
    image: arc.static('background.jpg', {stagePath: false})
    // or link to an external image URL such as ↓
    // image: ''
return {
    statusCode: 200,
    headers: {
      'content-type': 'text/html; charset=utf8',
      'cache-control': 'no-cache, no-store, must-revalidate, max-age=0, s-maxage=0'

arc.static is a helpful method that returns a URI path to your static asset file based on a lookup from static.json.

Web Inspector

background.jpg is now background-c580ddd102.jpg and we can let arc.static() keep track of the full file reference for you!

Next Steps