A simple implementation of the Distributed Snapshot algorithm
We all have bank accounts and do transactions everyday. When you start a transfer to another account, the money will be on the fly. It has been deducted from your account but has been not posted on the other account yet. The application should be able to take a snapshot of the global state, which means all the money in the accounts and on the fly.
We will assume multiple clients. Each client holds an account and have 2 operations:
- Transfer money.
- Start a snapshot.
- Each client should start with some amount money, say 1000. You can implement the transfer function as an Automatic Transfer. For example, you can set up something like every 10 seconds, each client has 0.2 probability to send a random amount of money to any of the other clients by sending a message to the other client. In order to detect messages in transit, incorporate some delay after the send comand is issued.
- Each client should be able to start a snapshot at anytime. A snapshot should be initialized by entering a command.
- When starting a client, it should know the ip and port of all other clients (You can keep clients connected all the time or connect them when they need to talk). You should have a configuration file that contains all the ip, port and account balance (To be simple, all clients can start with the same balance)
- You should log all necessary information on the console for the sake of debugging and demonstration, e.g. Client XX sent $ZZ dollar to Client YY. Client YY received $ZZ dollar from Client XX. Also, output the current balance when sending or receiving any money. When a snapshot has terminated, output the balance of each account, the money on the fly ( $XX is being sent from Client XX to Client YY) and the total amount of money (sum the account balance and the money on the fly). The sum should always add up to the same amount for all snapshots, since the overall money in the system is constant.
- You should add some delay (e.g. 5 seconds) when transferring money (starting a snapshot does not need any delay). This simulates the time for message passing and makes it easier for demoing concurrent events.
- Use message passing primitives TCP/UDP. You can decide which alternative and explore the trade-offs. We will be interested in hearing your experience.
- To start the client
python client.py <client_id> - Money transfer starts automatically between multiple clients with certain probability that is configurable in
config.json - To initiate snapshot, just type
snapshotafter the client is started. The snapshot state is logged in the console.