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 gsutil command line tool 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.

Example of serving from a Cloud Storage bucket

This simple example creates a Cloud Storage bucket and uploads static assets using Google Cloud 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.
```
gsutil mb gs://<your-bucket-name>
```
Set the ACL to grant read access to items in the bucket.
```
gsutil defacl set public-read gs://<your-bucket-name>
```
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.
```
gsutil -m rsync -r ./static gs://<your-bucket-name>/static
```

You can now access your static assets via https://storage.googleapis.com/<your-bucket-name>/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 for Go runtime version 1.15 and earlier, and version 1.18 and later. Note that you must update your app.yaml to use the new version. See Go runtime for more information about using the new runtimes.

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

v1.18 and later


// 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)
}

v1.15 and earlier


// 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 for Java runtime version 8 and version 11/17. Note that you must update your app.yaml to use the new version. See Java runtime for more information about using the new runtimes.

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 do not 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 stylesheet served from /stylesheets/styles.css.

version 11/17

<!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>

version 8

<!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 for Node.js runtime version 16 and earlier, and version 18 and later. Note that you must update your app.yaml to use the new version. See Node.js runtime for more information about using the new runtimes.

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 stylesheet 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:

runtime: php
env: flex

runtime_config:
  document_root: web

Python

The following sample demonstrates how to serve static files with your app for Python runtime version 3.7 and earlier. For Python version 3.8 and later, see Python runtime for more information about using newer versions.

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 stylesheet 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 stylesheet 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 for Ruby runtime for version 3.1 and earlier, and version 3.2. Note that you must update your app.yaml file to use the new version. See Ruby runtime for more information about using the new runtimes.

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 stylesheet 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 stylesheets:

version 3.2

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.

version 3.1 and earlier

doctype html
html
  head
    title Serving Static Files
    = stylesheet_link_tag "application", media: "all"
    = javascript_include_tag "application"
    = csrf_meta_tags
  body
    = yield

version 3.2

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

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

version 3.1 and earlier

The stylesheet itself is a Sass file located at ./app/assets/stylesheets/main.css.sass.

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

By default, Rails apps do not 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 for .NET runtime version 3.1 and earlier, and version 6 and later. Note that you must update your app.yaml file to use the new version. See .NET runtime for more information about using the new runtimes.

version 6 and later

<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();

version 3.1 and earlier

<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.