You want your systems to be resilient to failure and within Integration Cloud Oracle take care to ensure that there is always redundancy in the cloud based components to enable your integrations to continue to run despite potential failures of hardware or software. However the connectivity agent was a singleton until recently. That is no longer the case and you can now run more than one agent in an agent group.
An agent is a software component installed on your local system that "phones home" to Integration Cloud to allow message transfer between cloud and local systems without opening any firewalls. Agents are assigned to agent groups which are logical groupings of agents. A connection may make use of an agent group to gain access to local resources.
As of March 2019 this feature is now available on all OIC instances. This provides an HA solution for the agent, if one agent fails the other continues to process messages.
Agents require access to Integration Cloud using HTTPS, note that the agent may need to use a proxy to access Integration Cloud. This allows them to check for messages to be delivered from the cloud to local systems or vice versa. When using multiple agents in an agent group it is important that all agents in the group can access the same resources across the network. Failure to do this can cause unexpected failure of messages.
When running two agents in a group they process messages in an active-active model. All agents in the group will process messages, any given message will only be processed by a single agent. This provides both high availability and potentially improved throughput.
If resiliency is important then the HA agent group provides a reliable on-premise connectivity solution.