I have been organizing a distributed systems paper reading group in Berlin for the last year. We meet every other week discussing a paper in the distributed systems space. This could be anything from Chandy–Lamport’s algorithm for global distributed snapshots  to things like conflict free replicated datatypes . The event is open for anyone interested. I only ask people to come prepared.
In the last meeting (19th) we covered distributed hash tables. They play a crucial role in e.g. decentralized file sharing networks for example as directory services, simple key-value stores, or peer-to-peer membership management protocols.
Given its simplicity and wide spread industry adoption we chose to cover the distributed hash table Kademlia . I doubt I would do a better job explaining the concepts then the paper does, thus I recommend giving the paper itself a read.
Libp2p , a peer-to-peer networking library, implements the Kademlia paper with a couple of extensions. Multiple maintainers of the project attended the meeting sharing insights on implementation challenges like the suggested routing table optimizations.
For the next meeting we might stay within the Kademlia realm and look at different follow up papers covering its security aspects in byzantine environments  .
 Chandy, K. Mani, and Leslie Lamport. “Distributed snapshots: Determining global states of distributed systems.” ACM Transactions on Computer Systems (TOCS) 3.1 (1985): 63-75.
 Shapiro, Marc, et al. “A comprehensive study of convergent and commutative replicated data types.” (2011).
 Maymounkov, Petar, and David Mazieres. : A peer-to-peer information system based on the xor metric.” International Workshop on Peer-to-Peer Systems. Springer, Berlin, Heidelberg, 2002.
 Baumgart, Ingmar, and Sebastian Mies. “S/kademlia: A practicable approach towards secure key-based routing.” 2007 International Conference on Parallel and Distributed Systems. IEEE, 2007.
 Marcus, Yuval, Ethan Heilman, and Sharon Goldberg. “Low-Resource Eclipse Attacks on Ethereum’s Peer-to-Peer Network.” IACR Cryptology ePrint Archive 2018 (2018): 236.