Object Storage

Object Storage

OpenStack Object Storage (swift) service provides software that stores and retrieves data over HTTP. Objects (blobs of data) are stored in an organizational hierarchy that offers anonymous read-only access, ACL defined access, or even temporary access. Object Storage supports multiple token-based authentication mechanisms implemented via middleware.

Applications store and retrieve data in Object Storage via an industry-standard HTTP RESTful API. Back end components of Object Storage follow the same RESTful model, although some APIs, such as those managing durability, are kept private to the cluster. For more details on the API see the OpenStack Storage API.

The components of Object Storage are grouped into the following primary groups:

  1. Proxy services
  2. Auth services
  3. Storage services
    • Account service
    • Container service
    • Object service
_images/swift_network_diagram-1.png

An example diagram from the OpenStack Object Storage Administration Guide (2013)

Note

An Object Storage installation does not have to be on the Internet and could also be a private cloud with the public switch a part of the organization’s internal network infrastructure.

Network security

Securing the Object Storage service begins with securing the networking component. If you skipped the networking chapter, return to Networking.

The rsync protocol is used between storage service nodes to replicate data for high availability. In addition, the proxy service communicates with the storage service when relaying data back and forth between the client end-point and the cloud environment.

Caution

Object Storage does not employ encryption or authentication with inter-node communications. This is why you see a private switch or private network ([V]LAN) in the architecture diagrams. This data domain should be separate from other OpenStack data networks as well. For further discussion on security domains please see Security boundaries and threats.

Tip

Use a private (V)LAN network segment for your storage nodes in the data domain.

This necessitates that the proxy nodes have dual interfaces (physical or virtual):

  1. One as a public interface for consumers to reach.
  2. Another as a private interface with access to the storage nodes.

The following figure demonstrates one possible network architecture.

_images/swift_network_diagram-2.png

Object Storage network architecture with a management node (OSAM)

General service security

Run services as non-root user

We recommend that you configure the Object Storage service to run under a non-root (UID 0) service account. One recommendation is the user name swift with the primary group swift. Object Storage services include, for example, proxy-server, container-server, account-server. Detailed steps for setup and configuration can be found in the Add Object Storage chapter of the Installation Guide in the OpenStack Documentation index.

Note

The above link defaults to the Ubuntu version.

File permissions

The /etc/swift directory contains information about the ring topology and environment configuration. The following permissions are recommended:

# chown -R root:swift /etc/swift/*
# find /etc/swift/ -type f -exec chmod 640 {} \;
# find /etc/swift/ -type d -exec chmod 750 {} \;

This restricts only root to be able to modify configuration files while allowing the services to read them through their group membership in the swift group.

Securing storage services

The following are the default listening ports for the various storage services:

Service name Port Type
Account service 6002 TCP
Container service 6001 TCP
Object Service 6000 TCP
Rsync [1] 873 TCP
[1]If ssync is used instead of rsync, the object service port is used for maintaining durability.

Important

Authentication does not take place at the storage nodes. If you are able to connect to a storage node on one of these ports, you can access or modify data without authentication. In order to secure against this issue you should follow the recommendations given previously about using a private storage network.

Object Storage account terminology

An Object Storage account is not a user account or credential. The following explains the relations:

OpenStack Object Storage account Collection of containers; not user accounts or authentication. Which users are associated with the account and how they may access it depends on the authentication system used. See Object Storage authentication.
OpenStack Object Storage containers Collection of objects. Metadata on the container is available for ACLs. The meaning of ACLs is dependent on the authentication system used.
OpenStack Object Storage objects The actual data objects. ACLs at the object level are also possible with metadata and are dependent on the authentication system used.

At each level, you have ACLs that dictate who has what type of access. ACLs are interpreted based on what authentication system is in use. The two most common types of authentication providers used are Identity service (keystone) and TempAuth. Custom authentication providers are also possible. See Object Storage authentication for more information.

Securing proxy services

A proxy node should have at least two interfaces (physical or virtual): one public and one private. Firewalls or service binding might protect the public interface. The public facing service is an HTTP web server that processes end-point client requests, authenticates them, and performs the appropriate action. The private interface does not require any listening services, but is instead used to establish outgoing connections to storage nodes on the private storage network.

HTTP listening port

You should configure your web service as a non-root (no UID 0) user such as swift mentioned before. The use of a port greater than 1024 is required to make this easy and avoid running any part of the web container as root. Normally, clients using the HTTP REST API and performing authentication automatically retrieve the full REST API URL they require from the authentication response. OpenStack’s REST API allows for a client to authenticate to one URL and then be told to use a completely different URL for the actual service. For example, a Client authenticates to https://identity.cloud.example.org:55443/v1/auth and gets a response with their authentication key and Storage URL (the URL of the proxy nodes or load balancer) of https://swift.cloud.example.org:44443/v1/AUTH_8980.

The method for configuring your web server to start and run as a non-root user varies by web server and operating system.

Load balancer

If the option of using Apache is not feasible, or for performance you wish to offload your TLS work, you may employ a dedicated network device load balancer. This is a common way to provide redundancy and load balancing when using multiple proxy nodes.

If you choose to offload your TLS, ensure that the network link between the load balancer and your proxy nodes are on a private (V)LAN segment such that other nodes on the network (possibly compromised) cannot wiretap (sniff) the unencrypted traffic. If such a breach were to occur, the attacker could gain access to end-point client or cloud administrator credentials and access the cloud data.

The authentication service you use, such as Identity service (keystone) or TempAuth, will determine how you configure a different URL in the responses to end-point clients so they use your load balancer instead of an individual proxy node.

Object Storage authentication

Object Storage uses a WSGI model to provide for a middleware capability that not only provides general extensibility, but is also used for authentication of end-point clients. The authentication provider defines what roles and user types exist. Some use traditional user name and password credentials, while others may leverage API key tokens or even client-side x.509 certificates. Custom providers can be integrated in using custom middleware.

Object Storage comes with two authentication middleware modules by default, either of which can be used as sample code for developing a custom authentication middleware.

TempAuth

TempAuth is the default authentication for Object Storage. In contrast to Identity, it stores the user accounts, credentials, and metadata in object storage itself. More information can be found in the section The Auth System of the Object Storage (swift) documentation.

Keystone

Keystone is the commonly used Identity provider in OpenStack. It may also be used for authentication in Object Storage. Coverage of securing keystone is already provided in Identity.

Other notable items

In /etc/swift, on every node, there is a swift_hash_path_prefix setting and a swift_hash_path_suffix setting. These are provided to reduce the chance of hash collisions for objects being stored and avert one user overwriting the data of another user.

This value should be initially set with a cryptographically secure random number generator and consistent across all nodes. Ensure that it is protected with proper ACLs and that you have a backup copy to avoid data loss.

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.