openstack-manuals/doc/config-reference/source/messaging.rst

Message service

messaging/zaqar-conf.rst messaging/zaqar-api.rst messaging/zaqar-logging.rst messaging/zaqar-drivers.rst messaging/zaqar-storage-drivers.rst messaging/zaqar-transport-drivers.rst messaging/zaqar-notifications.rst messaging/zaqar-authentication.rst messaging/zaqar-pooling.rst messaging/logs.rst messaging/zaqar-cache.rst

The Message service is multi-tenant, fast, reliable, and scalable. It allows developers to share data between distributed application components performing different tasks, without losing messages or requiring each component to be always available.

The service features a RESTful API, which developers can use to send messages between various components of their SaaS and mobile applications, by using a variety of communication patterns.

Key features

The Message service provides the following key features:

• Choice between two communication transports. Both with Identity service support:
  • Firewall-friendly, HTTP-based RESTful API. Many of today's developers prefer a more web-friendly HTTP API. They value the simplicity and transparency of the protocol, its firewall-friendly nature, and its huge ecosystem of tools, load balancers and proxies. In addition, cloud operators appreciate the scalability aspects of the REST architectural style.
  • Websocket-based API for persistent connections. Websocket protocol provides communication over persistent connections. Unlike HTTP, where new connections are opened for each request/response pair, Websocket can transfer multiple requests/responses over single TCP connection. It saves much network traffic and minimizes delays.
• Multi-tenant queues based on Identity service IDs.
• Support for several common patterns including event broadcasting, task distribution, and point-to-point messaging.
• Component-based architecture with support for custom back ends and message filters.
• Efficient reference implementation with an eye toward low latency and high throughput (dependent on back end).
• Highly-available and horizontally scalable.
• Support for subscriptions to queues. Several notification types are available:
  • Email notifications.
  • Webhook notifications.
  • Websocket notifications.

Components

The Message service contains the following components:

• Transport back end. The Message service requires the selection of a transport specification responsible of the communication between the endpoints. In addition to the base driver implementation, the Message service also provides the means to add support for other transport mechanisms. The default option is WSGI.
• Storage back end. The Message service depends on a storage engine for message persistence. In addition to the base driver implementation, the Message service also provides the means to add support for other storage solutions. The default storage option is MongoDB.

To configure your Message service installation, you must define configuration options in these files:

• zaqar.conf. Contains most of the Message service configuration options. Resides in the /etc/zaqar directory. If there is a file zaqar.conf in ~/.zaqar directory, it is used instead of the one in /etc/zaqar directory.
• policy.json. Contains RBAC policy for all actions. Only applies to API v2. Resides in the /etc/zaqar directory. If there is a file policy.json in ~/.zaqar directory, it is used instead of the one in /etc/zaqar directory. See ../policy-json-file.

Note

The common configurations for shared service and libraries, such as database connections and RPC messaging, are described at common-configurations.