Cyraft

The objective is to implement the Raft algorithm as an exercise, with the intention of incorporating named topics into pycyphal.

This feature is significant because it enables Cyphal to serve as a communication layer between PX4 and ROS in the future.

(See UAVCAN as a middleware for ROS)

• Cyraft
  • TODO
  • Setup
  • Diagrams
    • demo_cyraft
    • DSDL datatypes
  • Sources

TODO

• Finish study pycyphal application layer
• demo_cyraft.py
  • Add instructions on how to interact with request_vote_rpc using yakut
  • Vscode debug setup
  • RaftNode unit tests
    • _unittest_raft_node_init
    • _unittest_raft_node_term_timeout
    • _unittest_raft_node_election_timeout
    • _unittest_raft_node_election_timeout_heartbeat
    • _unittest_raft_node_request_vote_rpc
    • _unittest_raft_node_append_entries_rpc
  • tests
    • leader_election.py
      • some warning need to be fixed here:
        • _unittest_raft_node_term_timeout
        • _unittest_raft_node_start_election
    • log_replication.py
      • _unittest_raft_log_replication
      • _unittest_raft_leader_changes
    • leader_commit needs to integrated/tested
  • Test using orchestration so there's 3 nodes running simultanously
    • use yakut to send AppendEntries requests
  • Add name resolution service
  • Monitor the network for online nodes
  • .env-variables and my_env.sh should be combined?
  • Implement Github CI
• Refactor code into cyraft

Questions:

• cyraft/node.py:
  • how to close properly? (fixed when running a single test, however still happens when running multiple)
• tests/leader_election.py:
  • difference of 1 term between node is not enough to determine who gets elected first (-> tested in raft_leader_election, test stage 8/9)
  • Some strange error prinouts in test stage 10/11

Code improvements:

• currently not using network to send requests, fix this
  • https://pycyphal.readthedocs.io/en/stable/api/pycyphal.application.html#rpc-service-clients-and-servers
  • in _send_heartbeat: there should be some timeout if node doesn't respond
• election and term timeouts can be done more cleanly
• move internal variables into RaftState (for example, only leader should have a term it is able to update)
  • Maybe not necessary? It's pretty clean as currently implemented I think.

Setup

• Clone repo

  git clone [email protected]:OpenCyphal-Garage/cyraft.git

• Virtual environment

  cd ~/cyraft
  python3 -m venv .venv
  source .venv/bin/activate

• Install requirements (pycyphal)

  cd ~/cyraft
  pip3 install -r requirements.txt

• git submodule update --init --recursive

• export CYPHAL_PATH="$HOME/cyraft/demo/custom_data_types:$HOME/cyraft/demo/public_regulated_data_types"

• Set up all necessary environment variables:

  cd ~/cyraft
  source my_env.sh

• Run the tests

  cd ~/cyraft
  pytest tests/

  

• Run the demo (This does not work yet)

  python3 demo/demo_cyraft.py

  NOTE: Sometimes this can give an error if it's using old datatypes, try to remove ~/.pycyphal and recompile DSDL datatypes (running previous command will do this automatically)

  rm -rf ~/.pycyphal

Diagrams

demo_cyraft

---
title: cyraft node X
---
flowchart TB
    subgraph 1X:org.opencyphal.pycyphal.raft.node
        direction TB
        subgraph heartbeat_publisher
            direction TB
            heartbeat_publisher_1[/uavcan.node.Heartbeat.1.0\]
        end
        heartbeat_publisher --> uavcan.node.heartbeat
        subgraph request_vote_rpc
            direction TB
            request_vote_1{{sirius_cyber_corp.RequestVoteRPC}}
        end
        10X:sirius_cyber_corp.RequestVote.Request --> request_vote_rpc
        request_vote_rpc --> 10X:sirius_cyber_corp.RequestVote.Response
        subgraph append_entries_rpc
            direction TB
            append_entries_1{{sirius_cyber_corp.AppendEntriesRPC}}
        end
        11X:sirius_cyber_corp.AppendEntriesRPC.Request --> append_entries_rpc
        append_entries_rpc --> 11X:sirius_cyber_corp.AppendEntriesRPC.Response
    end

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DSDL datatypes

---
title: RequestVote
---
classDiagram
    class RequestVote_Request{
        -uint64 term
        -uint64 last_log_index
        -uint64 last_log_term
    }

    class RequestVote_Response{
        -uint64 term
        -bool vote_granted
    }

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---
title: AppendEntries
---
classDiagram
    class AppendEntries_Request{
        -uint64 term
        -uint64 prev_log_index
        -uint64 prev_log_term
        -uint64 leaderCommit
        -LogEntry.1.0[<=1] log_entry
    }

    class AppendEntries_Response{
        -uint64 term
        -bool success
    }

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Sources

Raft paper

lynix94/pyraft

zhebrak/raftos

dronecan/libuavcan

An exploratory study: UAVCAN as a middleware for ROS

Allocators explanation in OpenCyphal/public_regulated_data_types