Gord-Overlay

• Gord is a reference implementation of Chord protocol.
• Gord-Overlay is a fork of Gord which is enabled to run on overlay network constructed with gossip-overlay lib
  • Additionaly, offers on-memory KVS store functionality

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What is Gord-Overlay?

Gord-Overlay is a DHT based distribute key-value store. Gord-Overlay will start as a REST server and your application can access data via REST.

How is it work?

Gord-Overlay is an implementation of DHT Chord and simple key-value store using the DHT. Chord protocol is an algorithm which extends consistent hashing. Gord-Overlay, using chord protocol, allocates a key to a node in distributed nodes ring.

In addition, KVS servers communicate with each other via REST to synchronize route information. Then, servers can query via REST to resolve other servers address and communicate with these. (REST I/F between servers is HTTP/2 but one for KVS accesses is HTTP/1.1)

Usage

• Gord-Overlay REST server reqires a hostname and port number pair
• If you specify 127.0.0.1:26000, the server will use 127.0.0.1:26000 to communication between other nodes and use 127.0.0.1:26001 to listen local REST request
• Specified hostname and port number pair is internally used as a KVS/Proxy server identifier, so you need to specify a unique pair for each server
• Additionaly, you need to specify address of a server which is already in the DHT network to join the network except the first server
• Proxy server introduced later section is a utility to connect to the overlay network from outside of the network
  • Proxy connect to bootstrap server. currently, proxy server at ryogrid.net:9999 is hard-coded
  • But you can change it by modifying this line
  • First proxy can launch with command ./third/gossip-port-forward/gossip-port-forward relay -p listenPort(required)
  • Other proxies can be bootstrap server also. But one proxy server which has global IP is needed at least on overlay network for NAT travarsal

## Build
make build

## Build proxy server for gordolctl connecting to overlay network
git pull
git submodule init
git submodule update
cd third/gossip-port-forward
go build -o gossip-port-forward gossip-port-forward.go

## Start proxy server (you do this only if you launch bootstrap proxy server myself)
./third/gossip-port-forward/gossip-port-forward both -a 127.0.0.1 -f forwardAddress(required) -l listenPort(required)

## Start KVS server (internally proxy server is launched) 
./gordolctl -l hostAndPort(required) -n existNodeHostAndPort(optional) 

Examples

1.A Start servers (after binary builds described above)

# launch 3 servers (3 shells are needed...)
cp ./third/gossip-port-forward/gossip-port-forward .

# each gordlctl internally launch gossip-port-forward process for myself
./gordolctl -l 127.0.0.1:20000
./gordolctl -l 127.0.0.1:20004 -n 127.0.0.1:20000 
./gordolctl -l 127.0.0.1:20008 -n 127.0.0.1:20004 

1.B Start servers (using docker-compose)

git clone https://github.com/ryogrid/gord-overlay.git
cd gord-overlay
git pull
git submodule init
git submodule update
docker-compose build && docker-compose up

2. Try!

# Query
curl -X POST -H "Content-Type: application/json" -d '{"key": "gord1"}' http://localhost:20001/server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord1"}' http://localhost:20005/server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord1"}' http://localhost:20009/server.ExternalService/FindHostForKey 

curl -X POST -H "Content-Type: application/json" -d '{"key": "gord2"}' http://localhost:20001/server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord2"}' http://localhost:20005 server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord2"}' http://localhost:20009 server.ExternalService/FindHostForKey 

curl -X POST -H "Content-Type: application/json" -d '{"key": "gord"}' localhost:20001 server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord"}' localhost:20005 server.ExternalService/FindHostForKey \
&& curl -X POST -H "Content-Type: application/json" -d '{"key": "gord"}' localhost:20009 server.ExternalService/FindHostForKey

# Put and Get value
curl -X POST -H "Content-Type: application/json" -d '{"key": "hoge", "value": "foobar"}' http://localhost:20001/server.ExternalService/PutValue
curl -X POST -H "Content-Type: application/json" -d '{"key": "hoge"}' http://localhost:20005/server.ExternalService/GetValue
curl -X POST -H "Content-Type: application/json" -d '{"key": "hoge"}' http://localhost:20009/server.ExternalService/GetValue

Development Memo

• here (Japanese)

TODO (not implemented part)

• Data replication
  • Puted data is stored only one server now
• Abnormal situation handling
  • Servers may crash when a node leavs DHT network or HTTP/2 connection is disconnected...
• Handling new server join and server leave after data writing started
  • When join, data delegation is needed
  • When leave, number of servers which have replica entries (key/value) same with leaved node should be keeped
    • Data replication to additinal server must occur