File Transfer Protocol

You can use the File Transfer Protocol (FTP) to interact with the objects on an AIStor Server.

You must specifically enable FTP or SFTP when starting the server. Enabling either server type does not affect other AIStor Server features.

This page uses the abbreviation FTP throughout, but you can use any of the supported FTP protocols described below.

When enabled, MinIO AIStor supports FTP access over the following protocols:

• SSH File Transfer Protocol (SFTP)

  SFTP is defined by the Internet Engineering Task Force (IETF) as an extension of SSH 2.0. SFTP allows file transfer over SSH for use with Transport Layer Security (TLS) and virtual private network (VPN) applications.

  Your FTP client must support SFTP.

• File Transfer Protocol over SSL/TLS (FTPS)

  FTPS allows for encrypted FTP communication with TLS certificates over the standard FTP communication channel. FTPS should not be confused with SFTP, as FTPS does not communicate over a Secure Shell (SSH).

  Your FTP client must support FTPS.

• File Transfer Protocol (FTP)

  Unencrypted file transfer.

  MinIO does not recommend using unencrypted FTP for file transfer.

When enabled, MinIO AIStor supports the following SFTP operations:

• get
• put
• ls
• mkdir
• rmdir
• delete

MinIO does not support either append or rename operations.

SFTP clients can only operate on the latest version of an object. Specifically:

• For read operations, MinIO AIStor only returns the latest version of the requested object(s) to the SFTP client.
• For write operations, MinIO AIStor applies normal versioning behavior and creates a new object version at the specified namespace. rm and rmdir operations create DeleteMarker objects.

SFTP access requires the same authentication as any other S3 client. MinIO AIStor supports the following authentication providers:

• MinIO AIStor Plugin users and their service accounts
• Active Directory/LDAP users and their service accounts
• OpenID/OIDC service accounts

STS credentials cannot access buckets or objects over SFTP.

Authenticated users can access buckets and objects based on the policies assigned to the user or parent user account.

The SFTP protocol does not require any of the admin:* permissions. You may not perform other MinIO AIStor admin actions with SFTP.

• Enable an FTP or SFTP port for the server.
• A port to use for the FTP commands and a range of ports to allow the FTP server to request to use for the data transfer.

1. Start MinIO AIStor with an FTP and/or SFTP port enabled.

   FTPS

   The following example starts MinIO AIStor with FTPS enabled.

   ./minio http://server{1...4}/disk{1...4}      \
   --ftp="address=:8021"                         \
   --ftp="passive-port-range=30000-40000"        \
   --ftp="tls-private-key=path/to/private.key"   \
   --ftp="tls-public-cert=path/to/public.crt"    \
   ...
   

   Omit tls-private-key and tls-public-cert to use the MinIO AIStor default TLS keys for FTPS. For more information, see the TLS on MinIO AIStor documentation.

   SFTP/FTP

   ./minio http://server{1...4}/disk{1...4}.            \
   --ftp="address=:8021"                                \
   --ftp="passive-port-range=30000-40000"               \
   --sftp="address=:8022"                               \
   --sftp="ssh-private-key=/home/miniouser/.ssh/id_rsa" \
   ...
   

   See the minio server --ftp and minio server --sftp for details on using these flags to start the MinIO service. To connect to the an FTP port with TLS (FTPS), pass the tls-private-key and tls-public-cert keys and values, as well, unless using the MinIO default TLS keys.

   The output of the command should return a response that resembles the following:

   MinIO FTP Server listening on :8021
   MinIO SFTP Server listening on :8022
   

2. Use your preferred FTP client to connect to the AIStor Server. You must connect as a user whose policies allow access to the desired buckets and objects.

   The specifics of connecting to MinIO AIStor depend on your FTP client. Refer to the documentation for your client.

   To connect over TLS or through SSH, you must use a client that supports the desired protocol.

3. Connect to MinIO AIStor.

   SFTP/FTP

   The following example connects to an SFTP server, and lists the contents of a bucket named runner.

   > sftp -P 8022 aistor@localhost
   minio@localhost's password:
   Connected to localhost.
   sftp> ls runner/
   chunkdocs  testdir
   

   FTPS

   The following uses the Linux FTP CLI client to connect to the AIStor Server using aistor credentials to list contents in a bucket named runner

   > ftp localhost -P 8021
   Connected to localhost.
   220 Welcome to MinIO FTP Server
   Name (localhost:user): aistor
   331 User name ok, password required
   Password:
   230 Password ok, continue
   Remote system type is UNIX.
   Using binary mode to transfer files.
   ftp> ls runner/
   229 Entering Extended Passive Mode (|||39155|)
   150 Opening ASCII mode data connection for file list
   drwxrwxrwx 1 nobody nobody            0 Jan  1 00:00 chunkdocs/
   drwxrwxrwx 1 nobody nobody            0 Jan  1 00:00 testdir/
   ...
   

4. Download an object.

   SFTP/FTP

   This example lists items in a bucket, then downloads the contents of the bucket.

   > sftp -P 8022 aistor@localhost
   aistor@localhost's password:
   Connected to localhost.
   sftp> ls runner/
   chunkdocs  testdir
   sftp> get runner/chunkdocs/metadata metadata
   Fetching /runner/chunkdocs/metadata to metadata
   metadata                               100%  226    16.6KB/s   00:00
   sftp>
   

   FTPS

   This example lists items in a bucket, then downloads the contents of the bucket.

   > ftp localhost -P 8021
   Connected to localhost.
   220 Welcome to MinIO FTP Server
   Name (localhost:user): aistor
   331 User name ok, password required
   Password:
   230 Password ok, continue
   Remote system type is UNIX.
   Using binary mode to transfer files.ftp> ls runner/chunkdocs/metadata
   229 Entering Extended Passive Mode (|||44269|)
   150 Opening ASCII mode data connection for file list
   -rwxrwxrwx 1 nobody nobody           45 Apr  1 06:13 chunkdocs/metadata
   226 Closing data connection, sent 75 bytes
   ftp> get
   (remote-file) runner/chunkdocs/metadata
   (local-file) test
   local: test remote: runner/chunkdocs/metadata
   229 Entering Extended Passive Mode (|||37785|)
   150 Data transfer starting 45 bytes
      45        3.58 KiB/s
   226 Closing data connection, sent 45 bytes
   45 bytes received in 00:00 (3.55 KiB/s)
   ...
   

On Kubernetes, you do not start the server yourself. Set objectStore.sftp in the Object Store Helm values and the AIStor Operator adds the SFTP flags to the server container for you.

The Operator exposes SFTP only. It does not start the FTP or FTPS listeners described above.

objectStore:
  sftp:
    enabled: true

Apply the configuration when deploying or upgrading your Object Store:

helm upgrade --install -n OBJECT-STORE-NAMESPACE OBJECT-STORE-NAME minio/aistor-objectstore -f aistor-objectstore-values.yaml

Replace OBJECT-STORE-NAMESPACE with your Object Store namespace and OBJECT-STORE-NAME with the Helm release name.

The Operator then:

• Starts the server with --sftp="address=:8022" and --sftp="ssh-private-key=...".
• Opens container port 8022 on each Object Store Pod.
• Creates a Service named minio-service-sftp in the Object Store namespace, listening on port 8022.

Setting enabled back to false removes the Service and restarts the Pods without the SFTP listener.

The Operator does not take a separate SSH host key. The server presents the Object Store’s TLS private key as its SSH host key.

By default, that is the first certificate in objectStore.certificates.server. If you list no certificates and leave objectStore.certificates.disableAutoCert at false, it is the certificate the Operator generates.

Because the host key is the TLS key, rotating the Object Store’s TLS certificate also changes the SSH host key. Clients that recorded the old key report a host key mismatch on their next connection.

To choose a different certificate, list it in objectStore.certificates.server after the first entry, then set domainName to a domain that certificate covers:

objectStore:
  certificates:
    server:
      - name: objectstore-default-tls
      - name: objectstore-sftp-tls
  sftp:
    enabled: true
    domainName: sftp.example.net

The server then uses the private key from objectstore-sftp-tls as its SSH host key.

domainName only selects the host key. It does not create DNS records, and it does not change how the Service is exposed.

The minio-service-sftp Service is a ClusterIP by default, which is reachable only from inside the cluster. Use the remaining objectStore.sftp fields to expose it:

For example, to reach SFTP on a fixed port on every node:

objectStore:
  sftp:
    enabled: true
    serviceType: NodePort
    nodePort: 31002

To test without exposing the Service, forward the port locally:

kubectl port-forward -n OBJECT-STORE-NAMESPACE svc/minio-service-sftp 8022:8022

Then connect as any user the Object Store can authenticate:

sftp -P 8022 MINIO-USER@localhost

The supported commands, versioning behavior, and authentication rules described on this page apply on Kubernetes without change.

MinIO AIStor supports mutual TLS (mTLS) certificate-based authentication on SFTP, where both the server and the client verify the authenticity of each other.

This type of authentication requires the following:

1. Public key file for the trusted certificate authority.
2. Public key file for the AIStor Server minted and signed by the trusted certificate authority.
3. Public key file for the user minted and signed by the trusted certificate authority for the client connecting by SFTP and located in the user’s .ssh folder (or equivalent for the operating system).

The keys must include a principals list of the user(s) that can authenticate with the key:

ssh-keygen -s ~/.ssh/ca_user_key -I miniouser -n miniouser -V +1h -z 1 miniouser1.pub

• -s specifies the path to the certificate authority public key to use for generating this key. The specified public key must have a principals list that includes this user.
• -I specifies the key identity for the public key.
• -n creates the user principals list for which this key is valid. You must include the user for which this key is valid, and the user must match the username in MinIO.
• -V limits the duration for which the generated key is valid. In this example, the key is valid for one hour. Adjust the duration for your requirements.
• -z adds a serial number to the key to distinguish this generated public key from other keys signed by the same certificate authority public key.

MinIO AIStor requires specifying the Certificate Authority used to sign the certificates for SFTP access. Start or restart the AIStor Server and specify the path to the trusted certificate authority’s public key using an --sftp="trusted-user-ca-key=PATH" flag:

minio server {path-to-server} --sftp="trusted-user-ca-key=/path/to/.ssh/ca_user_key.pub" {...other flags}

When connecting to the AIStor Server with SFTP, the client verifies the AIStor Server’s certificate. The client then passes its own certificate to the AIStor Server. MinIO AIStor verifies the key created above by comparing its value to the the known public key from the certificate authority provided at server startup.

Once MinIO AIStor verifies the client’s certificate, the user can connect to MinIO AIStor over SFTP:

sftp -P <SFTP port> <server IP>

The following procedure generates two key-value pairs, signs one with the other, then uses the resulting signed key to log in to the SFTP server.

1. Generate a key-value pair for the AIStor Server.

   ssh-keygen -f ./ca_user_key
   

2. Generate a key-value pair for the user.

   ssh-keygen -f ./minioadmin
   

   Replace minioadmin with the user accessing the AIStor Server by SFTP.

3. Sign the user key-value pair key with the AIStor Server key-value pair key.

   ssh-keygen -s ca_user_key -I minioadmin -n minioadmin -V +30d -z 1 minioadmin.pub
   

   Move the minioadmin.pub key to the same directory as minioadmin key-value pair, such as ~/.ssh/meaningful-directory.

4. Start or restart the MinIO Server passing the generated public keys.

   minio server --sftp="address=:8022" --sftp="ssh-private-key=/path/to/ca_user_key" --sftp="trusted-user-ca-key=/path/to/ca_user_key.pub"
   

5. Connect to the AIStor Server by SFTP.

   sftp -i ./minioadmin -oPort=8022 minioadmin@localhost
   

To force authentication to SFTP using LDAP or service account credentials, append a suffix to the username. Valid suffixes are either =ldap or =svc.

sftp -P 8022 my-ldap-user=svc@example.com:/bucket

sftp -P 8022 my-ldap-user=ldap@example.com:/bucket

• Replace my-ldap-user with the name of the LDAP administrator account.
• Replace aistor with the name of the user which runs the MinIO AIStor server processes.
• Replace example.com with the domain name of the MinIO AIStor server.