ZeroMQ
Overview
ZeroMQ is a minimalistic in memory message queuing library.
The connector is aimed at supporting PUB-SUB sockets and a forwarder component that can act as an interface for external systems to publish and subscribe messages.
Features:
- Configurable subscriptions.
- Configurable forwarder component that can receive messages from several publishers and forward to multiple subscribers.
- Support multipart message reception.
- With forwarder component enabled, we open a possibility to receive data from external systems other than out of the box published services (An use case for IOT based setup where devices communicate with each other using Mendix as an interface).
Documentation
ZeroMQ
ZeroMQ is a minimalistic in memory message queuing library.
The connector is aimed at supporting PUB-SUB sockets and a forwarder component that acts as an interface for external systems to publish and subscribe messages.
Refer to the docs for more information.
Features
Refer to the UseMe folder for configuration related information.
Subscription configuration
Multiple Subscription configuration is supported by persisting the connection information via entity ZMQSubscriber.
Use snippet SNIP_ZMQSubscriberConfiguration to visualize subscription configuration overview.
Configurations are created with the page ZMQSubscriber_NewEdit.
The Save action performs necessary validations and initiate or remove subscription for the configuration via ACT_SaveZMQSubscriber microflow. If you wish to use your own New/Edit page, please configure the microflow ACT_SaveZMQSubscriber for the Save action to avoid issues.
Name
Unique name for the configuration.
Subscription type
Local
Use this when the forwarder component is enabled. Refer Forwarder component section for more information. By this way, the configuration is setup to receive messages from the local publisher. Host and Port fields will be hidden for this configuration type.
External
This can be used with the forwarder component enabled or disabled. This configuration type connects to the external publishers.
Host
Host if the subscription type is External.
Port
Port if the subscription type is External.
Topic
Topic to subscribe.
Active
Yes - Initiates subscription for the specified topic.
No - Removes subscription for the specified topic.
Forwarder component
Forwarder component receives messages from several publishers and forwards them to multiple subscribers.
This component will be enabled if the constant ForwarderProxyEnabled is set to True.
It requires subscriber port to receive messages from several publishers and a publisher port to forward those messages for multiple subscribers.
The ports are configured via the following constants.
SubscriberPort - Defaulted to 5559
PublisherPort - Defaulted to 5560
Note:
With the forwarder component enabled and the subscription type for the configuration set to Local, subscription sockets are opened to listen on localhost and PublisherPort.
After startup
Please ensure to place the ASU_Startup microflow in your existing after startup microflow as sub microflow (or) in the Runtime settings of the project.
This ensures to start the forwarder component if enabled and open sockets for the active subscriptions configured during the application startup.
Before shutdown
Please ensure to place the BSD_Shutdown microflow in your existing before shutdown microflow as sub microflow (or) in the Runtime settings of the project.
This ensures to close the sockets initialized for the active configured subscriptions and shutdown the forwarder component if enabled.
On Message microflow
Each message is persisted in the form of file document and consolidated into a list. On message reception, microflow IVK_OnZMQMessage will be invoked with the following parameters.
ZMQSubscriber - Configuration responsible for the subscription.
MessageList - List of messages as specialized file document objects for the configured subscription.
Important Note:
- The first message should always contain the topic information as per the ZeroMQ standards, hence it shall be used for comparison with the configured topic and will not be considered for the message preparation. All the subsequent messages are captured as specialized file document objects.
- This implementation supports multipart message reception, where the sender can publish multiple messages as a block and it would be combined together as list of file document objects.
- The microflow is invoked asynchronously to avoid performance problems on long running operations. If the messages are to be processed in queue based fashion, it is up to the implementor to handle this behavior.
- Delete MessageList objects after completing the operations to avoid stale data and files being persisted.
Limitations
- Supports PUB-SUB sockets at the moment.
- The publisher(s) or subscriber(s) are not notified during disconnection. Connection will be re-established when the components are up again. This is the behavior of the ZeroMQ component itself which makes it lightweight. However, we can employ customized timeouts to handle such situations (or) choose a message broker like RabbitMQ 😉.