Serving static files

Applications often need to serve static files such as JavaScript, images, and CSS in addition to handling dynamic requests. Apps in the flexible environment can serve static files from a Google Cloud option like Cloud Storage, serve them directly, or use a third-party content delivery network (CDN).

Serving files from Cloud Storage

Cloud Storage can host static assets for dynamic web apps. The benefits of using Cloud Storage instead of serving directly from your app include:

Cloud Storage essentially works as a content delivery network. This does not require any special configuration because by default any publicly readable object is cached in the global Cloud Storage network.
Your app's load will be reduced by offloading serving static assets to Cloud Storage. Depending on how many static assets you have and the frequency of access, this can reduce the cost of running your app by a significant amount.
Bandwidth charges for accessing content can often be less with Cloud Storage.

You can upload your assets to Cloud Storage by using the Google Cloud CLI or the Cloud Storage API.

The Google Cloud Client Library provides an idiomatic client to Cloud Storage, for storing and retrieving data with Cloud Storage in an App Engine app.

Note that the PHP client also provides an API-backed stream wrapper which can be used to interact with Cloud Storage as a specialized file system.

Example of serving from a Cloud Storage bucket

This example creates a Cloud Storage bucket and uploads static assets using the gcloud CLI:

Create a bucket. It's common, but not required, to name your bucket after your project ID. The bucket name must be globally unique.
```
gcloud storage buckets create gs://<var>your-bucket-name</var>
```

Set the IAM policy to grant public read access to items in the bucket.

gcloud storage buckets add-iam-policy-binding gs://<var>your-bucket-name</var> --member=allUsers --role=roles/storage.objectViewer

Upload items to the bucket. The rsync command is typically the fastest and easiest way to upload and update assets. You could also use cp.
```
gcloud storage rsync ./static gs://<var>your-bucket-name</var>/static --recursive
```

You can now access your static assets via https://storage.googleapis.com/<var>your-bucket-name</var>/static/....

For more details on how to use Cloud Storage to serve static assets, including how to serve from a custom domain name, refer to How to Host a Static Website.

Serving files from other Google Cloud services

You also have the option of using Cloud CDN or other Google Cloud storage services.

Serving files directly from your app

Serving files from your app is typically straightforward, however, there are a couple drawbacks that you should consider:

Requests for static files can use resources that otherwise would be used for dynamic requests.
Depending on your configuration, serving files from your app can result in response latency, which can also affect when new instances are created for handling the load.

Example of serving static files with your app

Go

The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of Go by specifying the runtime version and operating system in your app.yaml file.

You can use the standard http.FileServer or http.ServeFile to serve files directly from your app.


// Package static demonstrates a static file handler for App Engine flexible environment.
package main

import (
	"fmt"
	"net/http"

	"google.golang.org/appengine"
)

func main() {
	// Serve static files from "static" directory.
	http.Handle("/static/", http.FileServer(http.Dir(".")))

	http.HandleFunc("/", homepageHandler)
	appengine.Main()
}

const homepage = `<!doctype html>
<html>
<head>
  <title>Static Files</title>
  <link rel="stylesheet" type="text/css" href="/static/main.css">
</head>
<body>
  <p>This is a static file serving example.</p>
</body>
</html>`

func homepageHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, homepage)
}

Java

The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of Java by specifying the runtime version and operating system in your app.yaml file.

The Java runtime's servlet container will use your app's deployment descriptor, web.xml file, to map URLs to servlets, including static assets. If you don't specify a web.xml, a default is used that maps everything to the default servlet.

In this example, ./src/main/webapp/index.html refers to a style sheet served from /stylesheets/styles.css.

<!doctype html>
<html>
<head>
<title>Static Files</title>
<link rel="stylesheet" type="text/css" href="/stylesheets/styles.css">
</head>
<body>
  <p>This is a static file serving example.</p>
</body>
</html>

The styles.css file is located at ./src/main/webapp/stylesheets/styles.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;
}

You can explicitly configure how static files are handled in the web.xml file. For example, if you wanted to map requests for all files that have the .jpg extension:

<servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.jpg</url-pattern>
</servlet-mapping>

If you are using a web framework, such as Play, you will need to refer to the framework's documentation on static assets.

Node.js

The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of Node.js by specifying the runtime version and operating system in your app.yaml file.

Most web frameworks include support for serving static files. In this sample, the application uses the express.static middleware to serve files from the ./public directory to the /static URL.

'use strict';

const express = require('express');
const app = express();

app.set('view engine', 'pug');

// Use the built-in express middleware for serving static files from './public'
app.use('/static', express.static('public'));

app.get('/', (req, res) => {
  res.render('index');
});

// Start the server
const PORT = parseInt(process.env.PORT) || 8080;
app.listen(PORT, () => {
  console.log(`App listening on port ${PORT}`);
  console.log('Press Ctrl+C to quit.');
});

The view refers to /static/main.css.

doctype html
html(lang="en")
  head
    title Static Files
    meta(charset='utf-8')
    link(rel="stylesheet", href="/static/main.css")
  body
    p This is a static file serving example.

The style sheet itself is located at ./public/css, which is served from /static/main.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;
}

Other Node.js frameworks, such as Hapi, Koa, and Sails typically support serving static files directly from the application. Refer to their documentation for details on how to configure and use static content.

PHP

The PHP runtime runs nginx to serve your app, which is configured to serve static files in your project directory. You must declare the document root by specifying document_root in your app.yaml file. You can use the sample application in this guide for any supported version of PHP by specifying the runtime version and operating system in your app.yaml file.

runtime: php
env: flex

runtime_config:
  document_root: web
  operating_system: ubuntu22
  runtime_version: 8.3

build_env_variables:
  NGINX_SERVES_STATIC_FILES: true

Python

The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of Python by specifying the runtime version and operating system in your app.yaml file.

Most web frameworks include support for serving static files. In this sample, the app uses Flask's built-in ability to serve files in ./static directory from the /static URL.

The app includes a view that renders the template. Flask automatically serves everything in the ./static directory without additional configuration.

import logging

from flask import Flask, render_template


app = Flask(__name__)


@app.route("/")
def hello():
    """Renders and serves a static HTML template page.

    Returns:
        A string containing the rendered HTML page.
    """
    return render_template("index.html")


@app.errorhandler(500)
def server_error(e):
    """Serves a formatted message on-error.

    Returns:
        The error message and a code 500 status.
    """
    logging.exception("An error occurred during a request.")
    return (
        f"An internal error occurred: <pre>{e}</pre><br>See logs for full stacktrace.",
        500,
    )


if __name__ == "__main__":
    # This is used when running locally. Gunicorn is used to run the
    # application on Google App Engine. See entrypoint in app.yaml.
    app.run(host="127.0.0.1", port=8080, debug=True)

The template rendered by the view includes a style sheet located at /static/main.css.

<!doctype html>
<html>
<head>
  <title>Static Files</title>
  <!--
  Flask automatically makes files in the 'static' directory available via
  '/static'.
  -->
  <link rel="stylesheet" type="text/css" href="/static/main.css">
</head>
<body>
  <p>This is a static file serving example.</p>
</body>
</html>

The style sheet is located at ./static/main.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;
}

Other Python frameworks, such as Django, Pyramid, and Bottle typically support serving static files directly from the app. Refer to their documentation for details on how to configure and use static content.

Ruby

Most web frameworks include support for serving static files. The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of Ruby by specifying the runtime version and operating system in your app.yaml file.

Sinatra

The Sinatra web framework serves files from the ./public directory by default. This app includes a view that refers to /application.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;
}

The style sheet is located at ./public/application.css which is served from /application.css.

Ruby on Rails

The Ruby on Rails web framework serves files from the ./public directory by default. Static JavaScript and CSS files can also be generated by the Rails asset pipeline.

These example apps contain a layout view that include all the application style sheets.

doctype html
html
  head
    title Serving Static Files
    link rel="stylesheet" href="/application.css"
    script src="/application.js"
  body
    p This is a static file serving example.

The style sheet itself is a .css file located at ./public/application.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;
}

By default, Rails apps don't generate or serve static assets when running in production.

The Ruby runtime executes rake assets:precompile during deployment to generate static assets and sets the RAILS_SERVE_STATIC_FILES environment variable to enable static file serving in production.

.NET

The following sample demonstrates how to serve static files with your app. You can use the sample application in this guide for any supported version of .NET by specifying the runtime version and operating system in your app.yaml file.

<html>
<head>
    <meta charset="utf-8" />
    <title>Hello Static World</title>
</head>
<body>
    <p>This is a static html document.</p>
    <p><img src="trees.jpg" /></p>
</body>
</html>

To enable static file serving, add:

app.UseDefaultFiles();
app.UseStaticFiles();

Serving from a third-party content delivery network

You can use any external third-party CDN to serve your static files and cache dynamic requests but your app might experience increased latency and cost.

For improved performance, you should use a third-party CDN that supports CDN Interconnect.