Chord implementation in C (Wrote for Linux). Supports everything but finger tables as of right now. Resilient to -r node failures. Handles many nodes joining with updates to successor lists and makes routing choices based on successor lists.

Protocol:

https://people.eecs.berkeley.edu/~istoica/papers/2003/chord-ton.pdf

Applications may then be built on top of this service that Chord provides. For example, a distributed hash table (DHT) application may distribute the key-value storage of a hash table across many peers and support the typical operations (i.e., insert, get, and remove). The DHT may be implemented on top of Chord by storing the key-value pairs at the node that Chord mapped to the given key.

To run:

1. Install google protocol buffers:

sudo apt-get install libprotobuf-c-dev protobuf-c-compiler

2. Execute:

An example usage to start a new Chord ring is:

  chord -a 128.8.126.63 -p 4170 --ts 30000 --tff 10000 --tcp 30000 -r 4

An example usage to join an existing Chord ring is:

  chord -a 128.8.126.63 -p 4171 --ja 128.8.126.63 --jp 4170 --ts 30000 --tff 10000 --tcp 30000 -r 4

1. -a = The IP address that the Chord client will bind to, as well as advertise to other nodes. Represented as an ASCII string (e.g., 128.8.126.63). Must be specified.

2. -p = The port that the Chord client will bind to and listen on. Represented as a base-10 integer. Must be specified.

3. --ja = The IP address of the machine running a Chord node. The Chord client will join this node’s ring. Represented as an ASCII string (e.g., 128.8.126.63). Must be specified if --jp is specified.

4. --jp = The port that an existing Chord node is bound to and listening on. The Chord client will join this node’s ring. Represented as a base-10 integer. Must be specified if --ja is specified.

5. --ts = The time in milliseconds between invocations of ‘stabilize’. Represented as a base-10 integer. Must be specified, with a value in the range of [1,60000].

6. --tff = The time in milliseconds between invocations of ‘fix fingers’. Represented as a base-10 integer. Must be specified, with a value in the range of [1,60000].

7. --tcp = The time in milliseconds between invocations of ‘check predecessor’. Represented as a base-10 integer. Must be specified, with a value in the range of [1,60000].

8. -r = The number of successors maintained by the Chord client. Represented as a base-10 integer. Must be specified, with a value in the range of [1,32].

9. -i = The identifier (ID) assigned to the Chord client which will override the ID computed by the SHA1 sum of the client’s IP address and port number. Represented as a string of 40 characters matching [0-9a-fA-F]. Optional parameter.

Commands:

There are two command that the Chord client must support: ‘Lookup’ and ‘PrintState’.

‘Lookup’ takes as input an ASCII string (e.g., “Hello”). The Chord client takes this string, hashes it to a key in the identifier space, and performs a search for the node that is the successor to the key (i.e., the owner of the key). The Chord client then outputs that node’s identifier, IP address, and port.

‘PrintState’ requires no input. The Chord client outputs its local state information at the current time, which consists of:

1. The Chord client’s own node information
2. The node information for all nodes in the successor list
3. The node information for all nodes in the finger table