This repo contains a toy gossip protocol implementation, basically used for didactic reasons. It can be used as a base to build and test gossip protocols.

My idea is to be able to use this as a base for crazy ideas and do a little bit of research about gossip and epidemic protocols over a distributed network.

The system contains a java server that listens to incoming calls, everything wrapped in a Docker container. The system also has a docker-compose file to simulate the distributed system.

The gossip protocol is basically a propagation using random IP's from the system range, so there is no assurance that it will work fine in all the cases. The file that contains this decision is com.github.lant.gossip.GossipStrategy . Modify it to get different results.

The current implementation is a very naive and primitive push based strategy:

• The nodes periodically propagate their value to 3 random nodes in the network.
• The nodes compare the value they receive with a version, right now it's the timestamp when the value was created by the propagator
• When a node receives a new value it propagates it immediately without waiting for the periodic propagation.
• If the value is the same, or an older one it silently ignores it.

These simple features are the basic ones for a proper gossip protocol.

Bootstrapping and peer discovery is also an interesting problem to solve. Currently when a peer starts it checks its network and starts querying the possible nodes in that network from bottom to top (starting at X.X.X.1 to X.X.X.X) in order to find another peer.

When it finds a peer they share their contact info. After that the initial bootstrap process is finished.

After the initial bootstrap to set up the system every subsequent interchange of information (value propagation) also contains information about the known nodes. So, the propagated values contain the value, the timestamp and information about the known peers from every peer. This way we guarantee that the peer contact information is continuously updated in all the peers.

For further ideas and information check the bibliography section.

To run the system you need to compile the code:

./gradlew installDist

and after that you can execute the docker:

docker-compose build
docker-compose up --scale node=10

This will start the 10 instances that will listen for new propagation values.

There is a script called propagate that's using the class: com.github.lant.gossip.Propagate in order to propagate values. It takes two parameters: port and value.

It will propagate the value to the node listening to that port. In order to execute it run docker ps to get the port mappings:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
b636473bfd3e        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 15 seconds       0.0.0.0:7012->7000/tcp   gossip_node_9
9922040ab0b9        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 14 seconds       0.0.0.0:7016->7000/tcp   gossip_node_6
4520094644e3        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 14 seconds       0.0.0.0:7017->7000/tcp   gossip_node_10
e54d26064f8e        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 15 seconds       0.0.0.0:7013->7000/tcp   gossip_node_8
41179de9eec4        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 14 seconds       0.0.0.0:7014->7000/tcp   gossip_node_5
70b2b5cc6831        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 15 seconds       0.0.0.0:7018->7000/tcp   gossip_node_7
11de74af17f6        gossip_node         "/bin/sh -c /gossip/…"   17 seconds ago      Up 15 seconds       0.0.0.0:7015->7000/tcp   gossip_node_4
b857e04524eb        gossip_node         "/bin/sh -c /gossip/…"   8 minutes ago       Up 17 seconds       0.0.0.0:7011->7000/tcp   gossip_node_3
25d4bd3acfc0        gossip_node         "/bin/sh -c /gossip/…"   8 minutes ago       Up 17 seconds       0.0.0.0:7009->7000/tcp   gossip_node_1
bf28387cf26c        gossip_node         "/bin/sh -c /gossip/…"   8 minutes ago       Up 16 seconds       0.0.0.0:7010->7000/tcp   gossip_node_2

and then just use one of the mapped ones:

./propagate -p 7009 --value asdf

This will propagate the value asdf into the nodes. It will use node_1 as the initial propagator.

Some interesting links about Gossip protocols:

• Gossip and Epidemic Protocols, Alberto Montresor
• Gossip Algorithms, University of Edimburgh
• Introduction to Gossip
• SWIM Gossip Protocol