Broker Software Wiki
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The broker pattern is an architectural pattern that can be used to structure distributed software systems with decoupled components that interact by remote procedure calls. A broker component is responsible for coordinating communication, such as forwarding requests, as well as for transmitting results and exceptions.[1]
The broker pattern is an architecture pattern that involves the use of an intermediary software entity called \"broker\" to facilitate communication between two or more software components. The broker acts as a \"middleman\" between the components, allowing them to communicate without being directly aware of each other's existence.
In the broker pattern, the broker is responsible for receiving messages from one component and forwarding them to the appropriate recipient. The components that communicate through the broker are known as servers or clients. The broker may also perform additional tasks, such as filtering, modifying messages, ensuring a quality of service (QoS) e.g. 0 for \"at most once\", or security , or providing additional services to the software components.
The broker pattern allows the components to remain decoupled and focused on their own responsibilities, while still being able to communicate and collaborate with other components in the system. It can also be used to reduce the number of dependencies between components, making the system more flexible and easier to maintain.
A message broker (also known as an integration broker or interface engine[1]) is an intermediary computer program module that translates a message from the formal messaging protocol of the sender to the formal messaging protocol of the receiver. Message brokers are elements in telecommunication or computer networks where software applications communicate by exchanging formally-defined messages.[1] Message brokers are a building block of message-oriented middleware (MOM) but are typically not a replacement for traditional middleware like MOM and remote procedure call (RPC).[2][3]
A message broker is an architectural pattern for message validation, transformation, and routing. It mediates communication among applications[vague], minimizing the mutual awareness that applications should have of each other in order to be able to exchange messages, effectively implementing decoupling.[4]
The primary purpose of a broker is to take incoming messages from applications and perform some action on them. Message brokers can decouple end-points, meet specific non-functional requirements, and facilitate reuse of intermediary functions. For example, a message broker may be used to manage a workload queue or message queue for multiple receivers, providing reliable storage, guaranteed message delivery and perhaps transaction management.
Message brokers are generally based on one of two fundamental architectures: hub-and-spoke and message bus. In the first, a central server acts as the mechanism that provides integration services, whereas with the latter, the message broker is a communication backbone or distributed service that acts on the bus.[3] Additionally, a more scalable multi-hub approach can be used to integrate multiple brokers.[3]
The MQTT protocol defines two types of network entities: a message broker and a number of clients. An MQTT broker is a server that receives all messages from the clients and then routes the messages to the appropriate destination clients.[16] An MQTT client is any device (from a micro controller up to a fully-fledged server) that runs an MQTT library and connects to an MQTT broker over a network.[17]
Information is organized in a hierarchy of topics. When a publisher has a new item of data to distribute, it sends a control message with the data to the connected broker. The broker then distributes the information to any clients that have subscribed to that topic. The publisher does not need to have any data on the number or locations of subscribers, and subscribers, in turn, do not have to be configured with any data about the publishers.
If a broker receives a message on a topic for which there are no current subscribers, the broker discards the message unless the publisher of the message designated the message as a retained message. A retained message is a normal MQTT message with the retained flag set to true. The broker stores the last retained message and the corresponding QoS for the selected topic. Each client that subscribes to a topic pattern that matches the topic of the retained message receives the retained message immediately after they subscribe. The broker stores only one retained message per topic.[18] This allows new subscribers to a topic to receive the most current value rather than waiting for the next update from a publisher.
When a publishing client first connects to the broker, it can set up a default message to be sent to subscribers if the broker detects that the publishing client has unexpectedly disconnected from the broker.
A minimal MQTT control message can be as little as two bytes of data. A control message can carry nearly 256 megabytes of data if needed. There are fourteen defined message types used to connect and disconnect a client from a broker, to publish data, to acknowledge receipt of data, and to supervise the connection between client and server.
The MQTT broker is a piece of software running on a computer (running on-premises or in the cloud), and could be self-built or hosted by a third party. It is available in both open source and proprietary implementations.
The broker acts as a post office. MQTT clients don't use a direct connection address of the intended recipient, but use the subject line called \"Topic\". Anyone who subscribes receives a copy of all messages for that topic. Multiple clients can subscribe to a topic from a single broker (one to many capability), and a single client can register subscriptions to topics with multiple brokers (many to one).
Each client can both produce and receive data by both publishing and subscribing, i.e. the devices can publish sensor data and still be able to receive the configuration information or control commands (MQTT is a bi-directional communication protocol). This helps in both sharing data, managing and controlling devices. A client cannot broadcast the same data to a range of topics, and must publish multiple messages to the broker, each with a single topic given.
With the MQTT broker architecture, the client devices and server application become decoupled. In this way, the clients are kept unaware of each other's information. MQTT, if configured to, can use TLS encryption with certificate, username and password protected connections. Optionally, the connection may require certification, in the form of a certificate file that a client provides and must match with the server's copy.
In case of failure, the broker software and clients can automatically hand over to a redundant/automatic backup broker. Backup brokers can also be set up to share the load of clients across multiple servers on site, in the cloud, or a combination of these.
The broker keeps track of all the session's information as the device goes on and off, in a function called \"persistent sessions\". In this state, a broker will store both connection info for each client, topics each client has subscribed to, and any messages for a topic with a QoS of 1 or 2.[21]
CORBA enables communication between software written in different languages and running on different computers. Implementation details from specific operating systems, programming languages, and hardware platforms are all removed from the responsibility of developers who use CORBA. CORBA normalizes the method-call semantics between application objects residing either in the same address-space (application) or in remote address-spaces (same host, or remote host on a network). Version 1.0 was released in October 1991.
CORBA uses an interface definition language (IDL) to specify the interfaces that objects present to the outer world. CORBA then specifies a mapping from IDL to a specific implementation language like C++ or Java. Standard mappings exist for Ada, C, C++, C++11, COBOL, Java, Lisp, PL/I, Object Pascal, Python, Ruby and Smalltalk. Non-standard mappings exist for C#, Erlang, Perl, Tcl and Visual Basic implemented by object request brokers (ORBs) written for those languages.
The CCM has a component container, where software components can be deployed. The container offers a set of services that the components can use. These services include (but are not limited to) notification, authentication, persistence and transaction processing. These are the most-used services any distributed system requires, and, by moving the implementation of these services from the software components to the component container, the complexity of the components is dramatically reduced.
The GIOP is an abstract protocol by which Object request brokers (ORBs) communicate. Standards associated with the protocol are maintained by the Object Management Group (OMG). The GIOP architecture provides several concrete protocols, including:
Message brokers can validate, store, route, and deliver messages to the appropriate destinations. They serve as intermediaries between other applications, allowing senders to issue messages without knowing where the receivers are, whether or not they are active, or how many of them there are. This facilitates decoupling of processes and services within systems.
In order to provide reliable message storage and guaranteed delivery, message brokers often rely on a substructure or component called a message queue that stores and orders the messages until the consuming applications can process them. In a message queue, messages are stored in the exact order in which they were transmitted and remain in the queue until receipt is confirmed.
Asynchronous messaging (15:11) refers to the type of inter-application communication that message brokers make possible. It prevents the loss of valuable data and enables systems to continue functioning even in the face of the intermittent connectivity or latency issues common on public networks. Asynchronous messaging guarantees that messages will be delivered once (and once only) in the correct order relative to other messages. 59ce067264