initial commit

Dockerfile

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+FROM debian:stable-slim
+
+# Install g++, make, OpenMPI, AND the OpenSSH server
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    g++ \
+    make \
+    openmpi-bin \
+    libopenmpi-dev \
+    openssh-server && \
+    rm -rf /var/lib/apt/lists/*
+
+# Create a directory for the SSH daemon to run (use -p to avoid errors)
+RUN mkdir -p /var/run/sshd
+
+# --- SSH Key Generation and Configuration ---
+# Generate a passwordless SSH key pair
+RUN ssh-keygen -t rsa -f /root/.ssh/id_rsa -N ''
+
+# Add the public key to the list of authorized keys for passwordless login
+RUN cat /root/.ssh/id_rsa.pub >> /root/.ssh/authorized_keys
+RUN chmod 600 /root/.ssh/authorized_keys
+
+# --- THIS IS THE NEW LINE ---
+# Create an SSH config file to disable host key checking
+RUN echo "Host *\n\tStrictHostKeyChecking no" >> /root/.ssh/config
+# --- END OF NEW LINE ---
+
+# Allow root login via SSH
+RUN sed -i 's/#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
+
+WORKDIR /app
+
+COPY . /app/
+
+# Compile using the MPI C++ compiler wrapper
+RUN mpic++ -O2 -std=c++17 -o mpi_task task.cpp

docker-compose.yml

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+services:
+  master:
+    build: .
+    container_name: pdc-master
+    volumes:
+      - ./hostfile:/app/hostfile
+    command: >
+      sh -c "/usr/sbin/sshd & sleep 5 && mpirun -np 4 --hostfile /app/hostfile --allow-run-as-root /app/mpi_task"
+    networks:
+      - pdcn
+
+  worker1:
+    build: .
+    container_name: pdc-worker1
+    command: /usr/sbin/sshd -D
+    networks:
+      - pdcn
+
+  worker2:
+    build: .
+    container_name: pdc-worker2
+    command: /usr/sbin/sshd -D
+    networks:
+      - pdcn
+
+  worker3:
+    build: .
+    container_name: pdc-worker3
+    command: /usr/sbin/sshd -D
+    networks:
+      - pdcn
+
+networks:
+  pdcn:
+    driver: bridge

hostfile

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+master slots=1
+worker1 slots=1
+worker2 slots=1
+worker3 slots=1

task.cpp

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+#include <iostream>
+#include <vector>
+#include <string>
+#include <algorithm>
+#include <mpi.h>
+
+int main(int argc, char** argv) {
+    MPI_Init(&argc, &argv);
+
+    int world_size;
+    MPI_Comm_size(MPI_COMM_WORLD, &world_size);
+
+    int world_rank;
+    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
+
+    if (world_rank == 0) {
+        // Master process
+        std::string message = "HELLOWORLDFROMMPI"; // A longer string to see the effect
+        std::cout << "Original Message: " << message << std::endl;
+        std::cout << "Total processes (world size): " << world_size << std::endl;
+
+        int msg_len = message.length();
+        int part_size = msg_len / world_size;
+        
+        // Send each worker its part of the string
+        for (int i = 1; i < world_size; ++i) {
+            int start_index = i * part_size;
+            // The last worker gets any remaining characters
+            int current_part_size = (i == world_size - 1) ? (msg_len - start_index) : part_size;
+            std::string part = message.substr(start_index, current_part_size);
+            MPI_Send(part.c_str(), part.size() + 1, MPI_CHAR, i, 0, MPI_COMM_WORLD);
+        }
+
+        // Master processes its own part
+        std::string master_part = message.substr(0, part_size);
+        std::reverse(master_part.begin(), master_part.end());
+
+        // A vector to store results in order
+        std::vector<std::string> results(world_size);
+        results[0] = master_part;
+
+        // Receive reversed parts from workers
+        for (int i = 1; i < world_size; ++i) {
+            char buffer[256];
+            MPI_Recv(buffer, 256, MPI_CHAR, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+            results[i] = std::string(buffer);
+        }
+
+        // Combine and print the final result
+        std::string final_result = "";
+        for (int i = 0; i < world_size; ++i) {
+            final_result += results[i];
+        }
+        std::cout << "Final Result: " << final_result << std::endl;
+
+    } else {
+        // Worker processes
+        char buffer[256];
+        MPI_Recv(buffer, 256, MPI_CHAR, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+        std::string part(buffer);
+        std::reverse(part.begin(), part.end());
+        MPI_Send(part.c_str(), part.size() + 1, MPI_CHAR, 0, 0, MPI_COMM_WORLD);
+    }
+
+    MPI_Finalize();
+    return 0;
+}