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Static Frontend, Container Backend

A simple frontend app with a containerized backend

A common pattern is to serve a static frontend application (e.g., React, Vue, Svelte) using Static Assets, then pass backend requests to a containerized backend application.

In this example, we'll show an example using a simple index.html file served as a static asset, but you can select from one of many frontend frameworks. See our Workers framework examples for more information.

For a full example, see the Static Frontend + Container Backend Template ↗.

Configure Static Assets and a Container

{
  "name": "cron-container",
  "main": "src/index.ts",
  "assets": {
    "directory": "./dist",
    "binding": "ASSETS"
  },
  "containers": [
    {
      "class_name": "Backend",
      "image": "./Dockerfile",
      "max_instances": 3
    }
  ],
  "durable_objects": {
    "bindings": [
      {
        "class_name": "Backend",
        "name": "BACKEND"
      }
    ]
  },
  "migrations": [
    {
      "new_sqlite_classes": [
        "Backend"
      ],
      "tag": "v1"
    }
  ]
}

Add a simple index.html file to serve

Create a simple index.html file in the ./dist directory.

index.html

 
<!DOCTYPE html>
<html lang="en">


<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Widgets</title>
  <script defer src="https://cdnjs.cloudflare.com/ajax/libs/alpinejs/3.13.3/cdn.min.js"></script>
</head>


<body>
  <div x-data="widgets()" x-init="fetchWidgets()">
    <h1>Widgets</h1>
    <div x-show="loading">Loading...</div>
    <div x-show="error" x-text="error" style="color: red;"></div>
    <ul x-show="!loading && !error">
      <template x-for="widget in widgets" :key="widget.id">
        <li>
          <span x-text="widget.name"></span> - (ID: <span x-text="widget.id"></span>)
        </li>
      </template>
    </ul>


    <div x-show="!loading && !error && widgets.length === 0">
      No widgets found.
    </div>


  </div>


  <script>
    function widgets() {
      return {
        widgets: [],
        loading: false,
        error: null,


        async fetchWidgets() {
          this.loading = true;
          this.error = null;


          try {
            const response = await fetch('/api/widgets');
            if (!response.ok) {
              throw new Error(`HTTP ${response.status}: ${response.statusText}`);
            }
            this.widgets = await response.json();
          } catch (err) {
            this.error = err.message;
          } finally {
            this.loading = false;
          }
        }
      }
    }
  </script>


</body>


</html>

In this example, we are using Alpine.js ↗ to fetch a list of widgets from /api/widgets.

This is meant to be a very simple example, but you can get significantly more complex. See examples of Workers integrating with frontend frameworks for more information.

Define a Worker

Your Worker needs to be able to both serve static assets and route requests to the containerized backend.

In this case, we will pass requests to one of three container instances if the route starts with /api, and all other requests will be served as static assets.

JavaScript
import { Container, getRandom } from "@cloudflare/containers";


const INSTANCE_COUNT = 3;


class Backend extends Container {
  defaultPort = 8080; // pass requests to port 8080 in the container
  sleepAfter = "2h"; // only sleep a container if it hasn't gotten requests in 2 hours
}


export default {
  async fetch(request, env) {
    const url = new URL(request.url);
    if (url.pathname.startsWith("/api")) {
      // note: "getRandom" to be replaced with latency-aware routing in the near future
      const containerInstance = await getRandom(env.BACKEND, INSTANCE_COUNT);
      return containerInstance.fetch(request);
    }


    return env.ASSETS.fetch(request);
  },
};

Define a backend container

Your container should be able to handle requests to /api/widgets.

In this case, we'll use a simple Golang backend that returns a hard-coded list of widgets.

server.go

 
package main


import (
  "encoding/json"
  "log"
  "net/http"
)


func handler(w http.ResponseWriter, r \*http.Request) {
  widgets := []map[string]interface{}{
    {"id": 1, "name": "Widget A"},
    {"id": 2, "name": "Sprocket B"},
    {"id": 3, "name": "Gear C"},
  }


  w.Header().Set("Content-Type", "application/json")
  w.Header().Set("Access-Control-Allow-Origin", "*")
  json.NewEncoder(w).Encode(widgets)


}


func main() {
  http.HandleFunc("/api/widgets", handler)
  log.Fatal(http.ListenAndServe(":8080", nil))
}