npm i s3proxy


Front AWS S3 with a web server that you control

by George Moon

1.6.3 (see all)License:Apache-2.0TypeScript:Not FoundCategories:Express Amazon Web Services API, Express Streaming, Express Amazon S3 API
npm i s3proxy


NPM Version NPM Downloads Node CI Docker Pulls

Use AWS S3 as the storage backend for a nodejs web server.


docker run --env BUCKET=mybucket --env PORT=8080 --publish 8080:8080 -t forkzero/s3proxy:1.6.1
curl http://localhost:8080/index.html  # serves s3://mybucket/index.html

If you need to pass temporary AWS credentials to your docker container (for local development, for example), generate the temporary credentials with the aws cli, store it in a file called credentials.json, and then mount that file into your container at /src/credentials.json. Note: this capability is disabled if NODE_ENV is undefined or NODE_ENV matches /^prod/i (e.g. prod or production, not case-sensitive).

aws sts get-session-token --duration 900 > credentials.json
docker run \
  -v $PWD/credentials.json:/src/credentials.json:ro \
  -e BUCKET=mybucket \
  -e PORT=8080 \
  -e NODE_ENV=dev \
  -p 8080:8080 \
  -t forkzero/s3proxy:1.6.1
curl http://localhost:8080/index.html  # serves s3://mybucket/index.html

Run it locally without docker:

npm install s3proxy express body-parser morgan express-request-id helmet
PORT=8080 BUCKET=mybucket node ./examples/express-s3proxy
curl http://localhost:8080/index.html  # serves s3://mybucket/index.html

Use the Range feature to get a certain byte range:

curl --range 0-99 http://localhost:8080/large.bin -o range.bin


  • Designed to be embedded into your nodejs application
  • Provides stream interface; stream files, even very large files, quickly and with a low memory footprint
  • HTTP GET requests are translated to S3 GetObject calls
  • HTTP HEAD requests are translated to S3 HeadObject calls
  • HTTP Range header is translated to S3 Range parameter (useful for working with large files, media files, etc)
  • Transparently handles retries against the AWS S3 backend
  • AWS S3 headers are provided as the HTTP response headers, including content-type and content-length
  • Easily integrated with common nodejs web frameworks; examples include http and express apps.
  • HealthCheck API verifies bucket connectivity and authentication, suitable for ELB health checks or monitoring services

Deployment Examples


Avoid S3 Dependencies for Your Application

Efficient, high-performance HTTP-based access to your S3 objects.

Private web endpoint

AWS S3 provides native web hosting, but it lacks fine-grained security controls. By hosting your own web server, you can use all of the AWS features including Security Groups, Route53, and network access control lists to control access to your resources

Dynamic content

AWS S3 web hosting only serves static content. By using S3 as the backend, you can stream files through your favorite templating engine for dynamic content on the fly.

Use Cases

Private artifact repo

A build process pushes RPM artifacts and metadata to a S3 bucket. The linux hosts need to use yum to install packages from this repo.

Rather than running yum-s3 and supplying credentials to each host, we use s3proxy to expose the files via HTTP like yum expects. The additional benefit is that only one piece of our infrastructure has a dependency on S3.

Quick Start

  1. Clone this repo, cd s3proxy
  2. Edit examples/express-basic.js, replace s3proxy-public with your S3 bucket name
  3. Install dependencies npm install
  4. Start the server PORT=8080 node express-basic
  5. Test it out (change index.html to the name of a file that exists in your bucket) curl http://localhost:3000/index.html

New Project

mkdir website
cd website
npm init
npm install --save express express-request-id morgan s3proxy
curl -O https://raw.githubusercontent.com/gmoon/s3proxy/master/examples/express-s3proxy.js
DEBUG=s3proxy PORT=8080 BUCKET=mybucket node express-s3proxy


s3proxy needs read access (s3:GetObject) on your bucket, and uses the AWS javascript sdk. You can provide credentials using any method supported:


The Environment Variables option is easy to get started, just make sure the variables are defined before you start the node process.

Alternatively, you can specify the profile to use on command line:

AWS_PROFILE=foo PORT=8080 node examples/express-basic.js

One way to test is to verify that your aws cli works from command line (substitute your bucket name):

aws s3 ls s3://s3proxy-public/


Here is the minimal set of permissions needed to run s3proxy (replace mybucket with your bucket name):

    "Version": "2012-10-17",
    "Statement": [
            "Sid": "s3proxyAccess",
            "Effect": "Allow",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::mybucket/*"

Special Characters in Object Names

As of version 1.5, the request URL is decoded prior to passing the key name to the S3 GetObject method. This has unit and integration test coverage and is tested against the special characters specified here across all three categories:

  • Safe characters
  • Characters that might require special handling
  • Characters to avoid

Testing from command-line:

start your server:

PORT=3000 node examples/express-basic.js

curl the url-encoded object:

# object name: specialCharacters!-_.*'()&$@=;:+  ,?\{^}%`]">[~<#|.
# url-encoded object name: specialCharacters!-_.*'()%26%24%40%3D%3B%3A%2B%20%20%2C%3F%5C%7B%5E%7D%25%60%5D%22%3E%5B~%3C%23%7C.
# bash-safe and url-encoded object name: specialCharacters\!-_.*'()%26%24%40%3D%3B%3A%2B%20%20%2C%3F%5C%7B%5E%7D%25%60%5D%22%3E%5B~%3C%23%7C.
curl -v "http://localhost:3000/specialCharacters\!-_.*'()%26%24%40%3D%3B%3A%2B%20%20%2C%3F%5C%7B%5E%7D%25%60%5D%22%3E%5B~%3C%23%7C."

Performance and Reliability

Performance is highly dependent on the types of files served and the infrastructure. See the Load Testing section for some data on different scenarios.

A tip to increase performance is to configure the aws-sdk to reuse TCP connections. In Load Testing, setting the AWS_NODEJS_CONNECTION_REUSE_ENABLED=1 environment variable reduced median response times by nearly 50% over a 60-second period.

When running s3proxy on an EC2 instance and comparing the artillery run (running on the same instance) against the AWS public S3 website, the response times for s3proxy were about 50% lower. This at least means s3proxy is not adding a lot of overhead over the AWS public S3 website.

Reliability can be achieved by fronting the web server with a Load Balancer. Each instance of s3proxy will utilize retries, which are enabled by the aws-sdk by default and can be further configured via the AWS SDK Global Configuration Object


  • npm install s3proxy --save

Express Example

  S3Proxy Express Framework Example

  Passes HTTP GET requests to s3proxy
  Start: PORT=3000 node express

const express = require('express');
const S3Proxy = require('s3proxy');

const port = process.env.PORT;
const app = express();
const proxy = new S3Proxy({ bucket: 's3proxy-public' });

  .get((req, res) => {

// Make sure to add an error handler (as shown below), otherwise your server will crash if the stream
// encounters an error (which occurs, for instance, when the requested object doesn't
// exist).
  .head(async (req, res) => {
    await proxy.head(req, res);
  .get((req, res) => {
      .on('error', () => res.end())

if (port > 0) {

module.exports = app;

HTTP Example

const S3Proxy = require('s3proxy');
const http = require('http');

const port = process.env.PORT;
const proxy = new S3Proxy({ bucket: 's3proxy-public' });

// Make sure to add an error handler (as shown below), otherwise your server will crash if the stream
// encounters an error (which occurs, for instance, when the requested object doesn't
// exist).
const server = http.createServer((req, res) => {
    .on('error', () => res.end())

if (port > 0) {

module.exports = server;

Configuring the AWS.S3 Object

The AWS.S3 object accepts options as defined here. These options can be passed through via the S3Proxy constructor.

const configuredProxy = new S3Proxy({
  bucket: 's3proxy-public',
  httpOptions: { connectTimeout: 1 },
  logger: console

init method

S3Proxy is a subclass of EventEmitter. That means you can register event listeners on the async calls.

proxy.on('init', () => {
proxy.on('error', (error) => {

init also accepts a callback function:

proxy.init((error) => {
  if (error) {
  else {


Test execution

The current test suite consists of some unit tests, but most of the tests are functional tests that require AWS S3 access. It uses a public bucket called s3proxy-public.

# Run the test suite
npm test

Load testing

Artillery can be used to send load to your endpoint. You can view the scenarios we use here.

If you run this, please make sure to run it against your bucket.

AWS EC2 Instance

Below are the results from a run on a t2.micro Amazon Linux 2 instance. Steps to run the load test:

# Install git and node
sudo yum install git
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.34.0/install.sh | bash
. ~/.nvm/nvm.sh
nvm install node

# Clone the s3proxy repo
git clone https://github.com/gmoon/s3proxy.git

# Run the test
cd s3proxy
npm install
AWS_NODEJS_CONNECTION_REUSE_ENABLED=1 PORT=3000 node examples/express-basic.js

# In a different console
cd s3proxy
npm run artillery-local

Response time p95 is less than 35ms and median response time is 12.3ms.

All virtual users finished
Summary report @ 01:36:53(+0000) 2020-08-17
  Scenarios launched:  1200
  Scenarios completed: 1200
  Requests completed:  1200
  Mean response/sec: 19.87
  Response time (msec):
    min: 8.1
    max: 275.9
    median: 12.3
    p95: 34.4
    p99: 62.9
  Scenario counts:
    0: 245 (20.417%)
    1: 225 (18.75%)
    2: 220 (18.333%)
    3: 260 (21.667%)
    4: 250 (20.833%)
    200: 730
    403: 220
    404: 250

Development Laptop

Below are the results from a run on a MacBook Pro with home internet (fast.com measured 61Mbps download and 5.0Mbps upload). It shows ~20 responses per second, the p95 response time was just under 250ms, and the median response time was 44.7ms.

All virtual users finished
Summary report @ 21:46:11(-0400) 2020-08-16
  Scenarios launched:  1200
  Scenarios completed: 1200
  Requests completed:  1200
  Mean response/sec: 19.86
  Response time (msec):
    min: 22.8
    max: 918.4
    median: 44.7
    p95: 246.3
    p99: 339.6
  Scenario counts:
    0: 248 (20.667%)
    1: 212 (17.667%)
    2: 256 (21.333%)
    3: 266 (22.167%)
    4: 218 (18.167%)
    200: 726
    403: 256
    404: 218

To execute the tests:

  1. start your local web server on port 8080
  2. run artillery
npm run artillery-local

Run GitHub Actions locally

Note: This is currently not working, as this stage fails: [Node CI/build-2] ❌ Failure - Configure AWS Credentials

brew install nektos/tap/act

Update dependencies, fix security vulnerabilities in dependencies

# see the status
npm outdated

# install npm-check-updates
npm install --global npm-check-updates

# update all dependencies
ncu --upgrade

# run audit
npm audit

# address audit issues
npm audit fix

Setup AWS Credentials for Github Actions


Add secrets to GitHub Secrets in the repo, per https://github.com/aws-actions/configure-aws-credentials

Release npm module

  1. git clone https://github.com/gmoon/s3proxy.git
  2. The version number exists in the documentation, search .md files and change to new version number: `grep -r --exclude-dir node_modules --exclude package.json --exclude package-lock.json 1.6.1 `
  3. npm version minor (or major or patch)
    • if you make a mistake:
      1. git reset --hard HEAD~1 Delete the most recent commit, destroying the work you've done
      2. git tag -d <tag_name> Delete the tag that was just created
  4. make all # run all tests
  5. npm publish
  6. git push
  7. git push origin <tag_name>
  8. create GitHub Release