This documentation is for WSO2 Private PaaS 4.1.0. View documentation for the latest release.
Page Comparison - Cartridge Agent (v.3 vs v.4) - WSO2 Private PaaS 4.1.0 - WSO2 Documentation

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In addition, Cartridge Agent has some extension points: Instance Started Extension, Start Servers Extension, Artifacts Updated Extension, Instance Activated Extension and Clean Extension. Cartridge developers can use these extension points to extend the cartridges in WSO2 Private PaaS. For example, the Instance Started Extension can be used to customize the cartridge at the point an instance has started.

Failover in Python Cartridge Agent

When communicating with the Message Broker, the Python Cartridge Agent (PCA) will go through the provided URL list and connect to the first broker that is available.
The listening subscriber client always ensures to maintain a connection with one of the brokers. The PCA periodically checks if the connected Message Broker is in fact alive or not. If the connected broker goes down, the PCA will go through the Message Broker list and select the first available broker. If none of the provided message brokers are online, the subscribing client will keep retrying until one broker becomes available. This logic is separately executed for each topic subscription.

The publishing client will publish the events to the first broker available. If none of the brokers are available it will keep retrying to publish the event, until the provided mb.publisher.timeout value is exceeded. The default value for this is 15 minutes. After the latter mentioned timeout, if the event is still unpublished, the event is dropped.
It is possible for the events to be published to one broker and for the intended consumers to be connected to another broker. However, if the Master/Slave deployment is done correctly, data sharing happens without an issue and this situation is not of any concern.