How to synchronize data between 2 different ROS nodes?

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Note: Q is not about time/timestamps synchronization. It's only about internal data.

Example: I have a node (A) running on a local machine under ROS. Node has internal data structure stored in memory. Let's say it's just a cpp std::unsorted_map. Now somewhere in the same local network on the other ROS machine I have another node (B). And B also has std::unsorted_map. Now I want 2 maps were always synced between 2 nodes so that they always were the same.

I know I can write a code to do it myself, but I'd like to get a hint for existing lib/framework/package allowing me to do that.