FOROS : Failover ROS framework

Purpose

FOROS is a ROS2 framework that provides the ability to construct a active-standby cluster based on the RAFT consensus algorithm.

Key Features

| Feature | Description | | —————– | ———————————————————————— | | Node Redundancy | Maintain a cluster of nodes runing in parallel to acheive a common goal. | | State Replication | Replicate a state of nodes for implementing a fault-tolerant service. |

Goals

This framework can tolerate fail-stop failures equal to the cluster size minus the quorum. | Cluster size (N) | Quorum (Q = N / 2 + 1) | Number of fault tolerant nodes (N - Q) | | :————–: | :——————–: | :————————————: | | 1 | 1 | 0 | | 2 | 2 | 0 | | 3 | 2 | 1 | | 4 | 3 | 1 | | 5 | 3 | 2 |

Prerequisites (Ubuntu)

Install ROS2

Supported distributions | OS | Distribution | Foros branch | | ———— | ——————————————— | ———— | | Ubuntu 20.04 | galactic | galactic | | Ubuntu 22.04 | humble | humble |

Install Foros

Option 1. Install Official Packages

for galactic

sudo apt install ros-galactic-foros ros-galactic-foros-examples ros-galactic-foros-inspector

for humble

sudo apt install ros-humble-foros ros-humble-foros-examples ros-humble-foros-inspector

Option 2. Build From Source

Install dependencies

sudo apt install libleveldb-dev libncurses-dev

Build

If you want to install to existing ROS2 workspace, please clone this source in the workspace in advance.

. /opt/ros/galactic/setup.bash
colcon build

Getting Started

In this section, we will create a cluster of 3 nodes that publishes a node ID every second. Lets’ assume that, | Cluster Name | Cluster Size | Node IDs in the Cluster | Topic Name | | :————-: | :———-: | :———————: | :————-: | | “hello_cluster” | 3 | 0, 1, 2 | “hello_cluster” |

1) Setup Environment

. /opt/ros/galactic/setup.bash
# If foros is installed in the custom workspace,
. {custom workspace}/install/setup.bash

2) Create ROS2 package

Let’s create the hello_cluster package that depends on foros, rclcpp, and std_msgs.

ros2 pkg create hello_cluster --description "Hello Cluster" --build-type ament_cmake --dependencies foros rclcpp std_msgs

3) Create “src/hello_cluster.cpp”

Most of the code is the same as the general ros2 code, except that the akit::failover::foros::ClusterNode class is used instead of rclcpp::Node when creating a node. Unlike rclcpp::Node that receives a node name as an argument, akit::failover::foros::ClusterNode receives a cluster name, node ID, and IDs of all nodes in the cluster as arguments. In fact, the node name of a cluster node is internally created by combining the cluster name and node ID.

For instance, if cluster name is “hello_cluster” and node id is 0, node name is created as “hello_cluster0”

```cpp // hello-cluster.cpp #include #include <rclcpp/rclcpp.hpp> #include <std_msgs/msg/string.hpp> #include #include

#include “akit/failover/foros/cluster_node.hpp”

using namespace std::chrono_literals;

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