I'm curious, what protocols do these distributed systems typically rely on? For instance, which algorithms are preferred for message ordering and concurrent synchronization? And how is data integrity maintained in cases of server instability?
How are Discord-style chat systems organized?
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When I first looked into these systems, the first thing that came to mind was, "How do they scale?" For example, during a project, we used Redis pub/sub even for a tiny chatbot, but then I realized how complex large-scale systems like Discord actually are. I'd heard that they use Snowflake-style IDs and Lamport clock-like logic for message ordering, but from what I've seen, most systems also use CRDTs—especially for real-time synchronization.
In cases of server instability, most modern systems rely on event sourcing and chronological logging. For instance, they write messages to an append-only log, and then all clients synchronize by reading this log. That way, if a server crashes, others can continue the log without data loss. Of course, when implementing this, we also learned that database replication requires consensus algorithms like Raft.
Recently, while trying to develop a Discord clone, my server crashed on the first attempt and all messages were lost. After that, I researched and started using the Raft algorithm instead of the simplest symmetric synchronization. While testing with a small group of servers, I encountered a few deadlock situations during leader elections, but eventually managed to ensure data consistency.