s3-sftp-proxy

s3-ftp-proxy is a tiny program that exposes resources on your AWS S3 buckets through SFTP protocol.

Usage

Usage of s3-sftp-proxy:
  -bind string
        listen on addr:port
  -config string
        configuration file (default "s3-sftp-proxy.toml")
  -debug
        turn on debugging output

• -bind

  Specifies the local address and port to listen on. This overrides the value of bind in the configuration file. If it is not present in the configuration file either, it defaults to :10022.

• -config

  Specifies the path to the configuration file. It defaults to "./s3-sftp-config.toml" if not given.

• -debug

  Turn on debug logging. The output will be more verbose.

Configuation

The configuration file is in TOML format. Refer to that page for the detailed explanation of the syntax.

Top level

host_key_file = "./host_key"
bind = "localhost:10022"
banner = """
Welcome to my SFTP server
"""
reader_lookback_buffer_size = 1048576
reader_min_chunk_size = 262144
lister_lookback_buffer_size = 100

# buckets and authantication settings follow...

• host_key_file (required)

  Specifies the path to the host key file (private key).

  The host key can be generated with ssh-keygen command:

   ssh-keygen -f host_key

• bind (optional, defaults to ":10022")

  Specifies the local address and port to listen on.

• banner (optional, defaults to an empty string)

  A banner is a message text that will be sent to the client when the connection is esablished to the server prior to any authentication steps.

• reader_lookback_buffer_size (optional, defaults to 1048576)

  Specifies the size of the buffer used to keep several amount of the data read from S3 for later access to it. The reason why such buffer is necessary is that SFTP protocol requires the data should be sent or retrieved on a random-access basis (i.e. each request contains an offset) while those coming from S3 is actually fetched in a streaming manner. In that we have to emulate block storage access for S3 objects, but chances are we don't need to hold the entire data with the reasonable SFTP clients.

• reader_min_chunk_size (optional, defaults to 262144)

  Specifies the amount of data fetched from S3 at once. Increase the value when you experience quite a poor performance.

• lister_lookback_buffer_size (optional, defalts to 100)

  Contrary to the people's expectation, SFTP also requires file listings to be retrieved in random-access as well.

• buckets (required)

  buckets contains records for bucket declarations. See Bucket Settings for detail.

• auth

  auth contains records for authenticator configurations. See Authenticator Settings for detail.

Bucket Settings

[buckets.test]
bucket = "BUCKET"
key_prefix = "PREFIX"
bucket_url = "s3://BUCKET/PREFIX"
profile = "profile"
region = "ap-northeast-1"
max_object_size = 65536
writable = false
readable = true
listable = true
auth = "test"
server_side_encryption = "kms"
sse_customer_key = ""
sse_kms_key_id = ""
keyboard_interactive_auth = false

[buckets.test.credentials]
aws_access_key_id = "aaa"
aws_secret_access_key = "bbb"

• bucket (required when bucket_url is unspecified)

  Specifies the bucket name.

• key_prefix (required when bucket_url is unspecified)

  Specifies the prefix prepended to the file path sent from the client. The key string is derived as follows:

    `key` = `key_prefix` + `path`
  

• bucket_url (required when bucket is unspecified)

  Specifies both the bucket name and prefix in the URL form. The URL's scheme must be s3, and the host part corresponds to bucket while the path part does to key_prefix. You may not specify bucket_url and either bucket or key_prefix at the same time.

• profile (optional, defaults to the value of AWS_PROFILE unless credentials is specified)

  Specifies the credentials profile name.

• region (optional, defaults to the value of AWS_REGION environment variable)

  Specifies the region of the endpoint.

• credentials (optional)

  • credentials.aws_access_key_id (required)

    Specifies the AWS access key.

  • credentials.aws_secret_access_key (required)

    Specifies the AWS secret access key.

• max_object_size (optional, defaults to unlimited)

  Specifies the maximum size of an object put to S3. This actually sets the size of the in-memory buffer used to hold the entire content sent from the client, as we have to calculate a MD5 sum for it before uploading there.

• readable (optional, defaults to true)

  Specifies whether to allow the client to fetch objects from S3.

• writable (optional, defaults to true)

  Specifies whether to allow the client to put objects to S3.

• listable (optional, defaults to true)

  Specifies whether to allow the client to list objects in S3.

• server_side_encryption (optional, defaults to "none")

  Specifies which server-side encryption scheme is applied to store the objects. Valid values are: "aes256" and "kms".

• sse_customer_key (required when server_side_encryption is set to "aes256")

  Specifies the base64-encoded encryption key. As the cipher is AES256-CBC, the key must be 256-bits long (32 bytes)

• sse_kms_key_id (required when server_side_encryption is est to "kms")

  Specifies the CMK ID used for the server-side encryption using KMS.

• keyboard_interactive_auth (optional, defaults to false)

  Enables keyboard interactive authentication if set to true.

• auth (required)

  Specifies the name of the authenticator.

Authenticator Settings

[auth.test]
type = "inplace"

# authenticator specific settings follow

• type (required)

  Specifies the authenticator implementation type. Currently "inplace" is the only valid value.

• users (required when type is "inplace")

  Contains user records as a dictionary.

In-place authenticator

In-place authenticator reads the credentials directly embedded in the configuration file. The user record looks like the following:

[auth.test]
type = "inplace"

[auth.test.users.user0]
password = "test"
public_keys = """
ssh-rsa AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
ssh-rsa AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
"""

[auth.test.users.user1]
password = "test"
public_keys = """
ssh-rsa AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
ssh-rsa AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
"""

Or

[auth.test]
type = "inplace"

[auth.test.users]
user0 = { password="test", public_keys="..." }
user1 = { password="test", public_keys="..." }

• (key) (appears as user0 or user1 in the above example)

  Specifies the name of the user.

• password (optional)

  Specifies the password in a clear-text form.

• public_keys (optional)

  Specifies the public keys authorized to use in authentication. Multiple keys can be specified by delimiting them by newlines.