Investigate persistence in database and/or blockchain

[sadhbh-c0d3]

Currently we persist all state in JSON files on the host. This works for tiny traffic, but once we scale up we will need more robust persistence system.

• MariaDB - well tested in the batlefield of HFT, fantastic SQL database with several engines to pick from
• Hazelcast - distributed data propagation, distributes concurrent data structures like Map or Set
• MongoDB - well tested in the micro-services, fantastic for storing non-tabular data
• Blockchain - unforgeable, allows to store information in a way that it cannot be edited or tampered with

Proposal:

• Use Hazelcast to propagate data between service components
• Develop DB writer as Hazelcast client (HC has persistence on its own too!)
• Develop Blockchain engraver, which will make some longer standing data engraved into chain and prevent any further changes to it