caddy-s3-proxy

caddy-s3-proxy allows you to proxy requests directly from S3.

S3 does have the website option, in which case, a normal reverse proxy could be used to display S3 data. However, it is sometimes inconvient to do that. This module lets you access S3 data even if website access is not configured on your bucket.

Making a version of caddy with this plugin

With caddy 2 you can use xcaddy to build a version of caddy with this plugin installed. To install xcaddy do:

go install github.com/caddyserver/xcaddy/cmd/xcaddy@latest

This repo has a Makefile to make it easier to build a new version of caddy with this plugin. Just type:

make build

You can run make docker do build a local image you can test with.

Configuration

The Caddyfile directive would look something like this:

    s3proxy [<matcher>] {
        bucket <bucket_name>
        region <region_name>
                profile <aws profile>
        index  <list of index file names>
        endpoint <alternative S3 endpoint>
        root   <key prefix>
        enable_put
        enable_delete
        force_path_style
        errors <http status> <S3 key to a custom error page for this http status>
        errors <S3 key to a default error page>
        browse [<path to template>]
    }

option	type	required	default	help
bucket	string	yes		S3 bucket name
region	string	yes-ish	env AWS_REGION	S3 region - if not give in the Caddyfile then AWS_REGION env var must be set.
profile	string	no	empty string	AWS profile if using shared credentials files.
endpoint	string	no	aws default	S3 hostname
index	string[]	no	[index.html, index.txt]	Index files to look up for dir path
root	string	no		Set a "prefix" to be added to key
enable_put	bool	no	false	Allow PUT method to be sent through proxy
enable_delete	bool	no	false	Allow DELETE method to be sent through proxy
force_path_style	bool	no	false	Set this to `true` to force S3 request to use path-style addressing
use_accelerate	bool	no	false	Set this to `true` to enable S3 Accelerate feature
errors	[int, ] string	no		Custom error page or use "pass_through" to write nothing for errors.
browse	[string]	no		Turns on a directory view for partial keys, an optional path to a template can be given

Credentials

This module uses the default providor chain to get credentials for access to S3. This provides several more secure options to provide credentials for accessing S3 without putting the credentials in the Caddyfile. The methods include (and are looked for in this order):

1) Environment variables. I.e. AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY

2) Shared credentials file. (Located at ~/.aws/credentials) (You may pass the optional profile directive to select specific credentials.)

3) If your application uses an ECS task definition or RunTask API operation, IAM role for tasks.

4) If your application is running on an Amazon EC2 instance, IAM role for Amazon EC2.

For much more detail on the various options for setting AWS credentials see here: https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html

Works with localstack!

The s3 proxy works great with localstack for local testing. Just set the endpoint directive to your localstack instance. You will also want to set the force_path_style directive as well since localstack currently does not support virtual style addressing. In fact, all of our examples use localstack - check out the examples directory.

Handling errors

When accessing S3 you may get errors like keyNotFound, bucket does not exist, or ACL permissions problems. By default this proxy will map those errors to an http error - like 404, 403 or 500.

However, with the errors directive you have a couple of more options. You can specify a S3 key that may contain HTML to display rather than just returning an error code. This can be done for a specific error or all errors. For example,

errors 403 /key/path/to/permissionerr.html
errors /key/path/to/defaulterr.html

This will display the page permissionerr.html for any 403 errors and defaulterr.html for all other errors.

There is a special option to "pass through" on an error and let the next Caddy handler deal with the request. For example,

errors 404 pass_through
errors /key/path/to/defaulterr.html

Will pass 404 errors onto the next handler. All other errors will show the page defaulterr.html.

Note: The errors direction only applies to GET method requests. PUT and DELETE errors just return the code.

Examples you can play with

In the examples directory is an example of using the s3proxy with localstack. Localstack contains a working version of S3 you can use for local development.

Check out the examples here. You can also just run make example to build a docker image with the plugin and launch the compose example.