serverless-s3-local

v0.9.X is under developing. This version will have BREAKING CHANGES.

serverless-s3-local is a Serverless plugin to run S3 clone in local. This is aimed to accelerate development of AWS Lambda functions by local testing. I think it is good to collaborate with serverless-offline.

Installation

Use npm

npm install serverless-s3-local --save-dev

Use serverless plugin install

sls plugin install --name serverless-s3-local

Example

serverless.yaml

service: serverless-s3-local-example
provider:
  name: aws
  runtime: nodejs18.x
plugins:
  - serverless-s3-local
  - serverless-offline
custom:
# Uncomment only if you want to collaborate with serverless-plugin-additional-stacks
# additionalStacks:
#    permanent:
#      Resources:
#        S3BucketData:
#            Type: AWS::S3::Bucket
#            Properties:
#                BucketName: ${self:service}-data
  s3:
    host: localhost
    directory: /tmp
resources:
  Resources:
    NewResource:
      Type: AWS::S3::Bucket
      Properties:
        BucketName: local-bucket
functions:
  webhook:
    handler: handler.webhook
    events:
      - http:
        method: GET
        path: /
  s3hook:
    handler: handler.s3hook
    events:
      - s3: local-bucket
        event: s3:*

handler.js (AWS SDK v2)

const AWS = require("aws-sdk");

module.exports.webhook = (event, context, callback) => {
  const S3 = new AWS.S3({
    s3ForcePathStyle: true,
    accessKeyId: "S3RVER", // This specific key is required when working offline
    secretAccessKey: "S3RVER",
    endpoint: new AWS.Endpoint("http://localhost:4569"),
  });
  S3.putObject({
    Bucket: "local-bucket",
    Key: "1234",
    Body: new Buffer("abcd")
  }, () => callback(null, "ok"));
};

module.exports.s3hook = (event, context) => {
  console.log(JSON.stringify(event));
  console.log(JSON.stringify(context));
  console.log(JSON.stringify(process.env));
};

handler.js (AWS SDK v3)

const { S3Client, PutObjectCommand } = require("@aws-sdk/client-s3");

module.exports.webhook = (event, context, callback) => {
  const client = new S3Client({
    forcePathStyle: true,
    credentials: {
      accessKeyId: "S3RVER", // This specific key is required when working offline
      secretAccessKey: "S3RVER",
    },
    endpoint: "http://localhost:4569",
  });
  client
    .send(
      new PutObjectCommand({
        Bucket: "local-bucket",
        Key: "1234",
        Body: Buffer.from("abcd"),
      })
    )
    .then(() => callback(null, "ok"));
};

module.exports.s3hook = (event, context) => {
  console.log(JSON.stringify(event));
  console.log(JSON.stringify(context));
  console.log(JSON.stringify(process.env));
};

Configuration options

Configuration options can be defined in multiple ways. They will be parsed with the following priority:

custom.s3 in serverless.yml
custom.serverless-offline in serverless.yml
Default values (see table below)

Option	Description	Type	Default value
address	The host/IP to bind the S3 server to	string	`'localhost'`
host	The host where internal S3 calls are made. Should be the same as address	string
port	The port that S3 server will listen to	number	`4569`
directory	The location where the S3 files will be created. The directory must exist, it won't be created	string	`'./buckets'`
accessKeyId	The Access Key Id to authenticate requests	string	`'S3RVER'`
secretAccessKey	The Secret Access Key to authenticate requests	string	`'S3RVER'`
cors	Path to the S3 CORS configuration XML relative to the project root. See AWS docs	string \| Buffer
website	Path to the S3 Website configuration XML relative to the project root. See AWS docs	string \| Buffer
noStart	Set to true if you already have an S3rver instance running	boolean	`false`
allowMismatchedSignatures	Prevent SignatureDoesNotMatch errors for all well-formed signatures	boolean	`false`
silent	Suppress S3rver log messages	boolean	`false`
serviceEndpoint	Override the AWS service root for subdomain-style access	string	`amazonaws.com`
httpsProtocol	To enable HTTPS, specify directory (relative to your cwd, typically your project dir) for both cert.pem and key.pem files.	string
vhostBuckets	Disable vhost-style access for all buckets	boolean	`true`
buckets	Extra bucket names will be created after starting S3 local	string

Feature

Start local S3 server with specified root directory and port.
Create buckets at launching.
Support serverless-plugin-additional-stacks
Support serverless-webpack
Support serverless-plugin-existing-s3
Support S3 events.

Working with IaC tools

If your want to work with IaC tools such as terraform, you have to manage creating bucket process. In this case, please follow the below steps.

Comment out configurations about S3 Bucket from resources section in serverless.yml.

#resources:
#  Resources:
#    NewResource:
#      Type: AWS::S3::Bucket
#      Properties:
#        BucketName: local-bucket

Create bucket directory in s3rver working directory.

$ mkdir /tmp/local-bucket

Triggering AWS Events offline

This plugin will create a temporary directory to store mock S3 info. You must use the AWS cli to trigger events locally. First, using aws configure set up a new profile, i.e. aws configure --profile s3local. The default creds are

aws_access_key_id = S3RVER
aws_secret_access_key = S3RVER

You can now use this profile to trigger events. e.g. to trigger a put-object on a file at ~/tmp/userdata.csv in a local bucket run: aws --endpoint http://localhost:4569 s3 cp ~/tmp/data.csv s3://local-bucket/userdata.csv --profile s3local

You should see the event trigger in the serverless offline console: info: PUT /local-bucket/user-data.csv 200 16ms 0b and a new object with metadata will appear in your local bucket.

Enabling CORS

Create an .xml file with CORS configuration. See AWS docs

E.g. to enable CORS for GET requests:

<CORSConfiguration>
  <CORSRule>
    <AllowedOrigin>*</AllowedOrigin>
    <AllowedMethod>GET</AllowedMethod>
    <AllowedHeader>*</AllowedHeader>
    <MaxAgeSeconds>30000</MaxAgeSeconds>
    <ExposeHeader>x-amz-server-side-encryption</ExposeHeader>
  </CORSRule>
</CORSConfiguration>

Reference the file in your config:

custom:
  s3:
    host: localhost
    directory: /tmp
    cors: ./path/to/cors.xml

Running on Node 18 or higher

You may meet an error such as following on Node 18 or higher.

Error: error:0308010C:digital envelope routines::unsupported
      at Cipheriv.createCipherBase (node:internal/crypto/cipher:122:19)
      at Cipheriv.createCipherWithIV (node:internal/crypto/cipher:141:3)
      at new Cipheriv (node:internal/crypto/cipher:249:3)

...

In this case, please set the following environemnt variable.

export NODE_OPTIONS=--openssl-legacy-provider

License

This software is released under the MIT License, see LICENSE.