Add pure MPI sample that run as non-root

examples/pi/Dockerfile

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+FROM debian:buster
+
+RUN apt update && apt install -y --no-install-recommends \
+			build-essential \
+			libopenmpi-dev \
+			openmpi-bin \
+			openssh-server \
+			openssh-client \
+			&& rm -rf /var/lib/apt/lists/*
+# Add priviledge separation directoy to run sshd as root.
+RUN mkdir -p /var/run/sshd
+# Add capability to run sshd as non-root.
+RUN setcap CAP_NET_BIND_SERVICE=+eip /usr/sbin/sshd
+
+RUN useradd -m mpiuser
+WORKDIR /home/mpiuser
+COPY --chown=mpiuser sshd_config .sshd_config
+RUN sed -i 's/[ #]\(.*StrictHostKeyChecking \).*/ \1no/g' /etc/ssh/ssh_config
+COPY pi.cc /src/pi.cc
+RUN mpic++ /src/pi.cc -o /home/mpiuser/pi

examples/pi/README.md

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+# Pure MPI example
+
+This example shows to run a pure MPI application.
+
+The program prints some basic information about the workers.
+Then, it calculates an approximate value for pi.
+
+## How to build Image
+
+```bash
+docker build -t mpi-pi .
+```
+
+## Create MPIJob
+
+Modify `pi.yaml` to set up the image name from your own registry.
+
+Then, run:
+
+```
+kubectl create -f pi.yaml
+```
+
+The YAML shows how to run the binaries as a non-root user.

examples/pi/pi.cc

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+// Copyright 2021 The Kubeflow Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "mpi.h"
+#include <random>
+#include <cstdio>
+
+int main(int argc, char *argv[]) {
+  int rank, workers, proc_name_size;
+  MPI_Init(&argc, &argv);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+  MPI_Comm_size(MPI_COMM_WORLD, &workers);
+  if (rank == 0) {
+    printf("Workers: %d\n", workers);
+  }
+  char hostname[MPI_MAX_PROCESSOR_NAME];
+  MPI_Get_processor_name(hostname, &proc_name_size);
+  printf("Rank %d on host %s\n", rank, hostname);
+
+  std::minstd_rand generator(rank);
+  std::uniform_real_distribution<double> distribution(-1.0, 1.0);
+  double x, y;
+  long long worker_count = 0;
+  int worker_tests = 100000000;
+  for (int i = 0; i < worker_tests; i++) {
+    x = distribution(generator);
+    y = distribution(generator);
+    if (x * x + y * y <= 1.0) {
+      worker_count++;
+    }
+  }
+  long long total_count = 0;
+  MPI_Reduce(&worker_count, &total_count, 1, MPI_LONG_LONG, MPI_SUM, 0, MPI_COMM_WORLD);
+  if (rank == 0) {
+    double pi = 4 * (double)total_count / (double)(worker_tests) / (double)(workers);
+    printf("pi is approximately %.16lf\n", pi);
+  }
+  MPI_Finalize();
+  return 0;
+}

examples/pi/pi.yaml

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+apiVersion: kubeflow.org/v2beta1
+kind: MPIJob
+metadata:
+  name: pi
+spec:
+  slotsPerWorker: 1
+  cleanPodPolicy: Running
+  sshAuthMountPath: /home/mpiuser/.ssh
+  mpiReplicaSpecs:
+    Launcher:
+      replicas: 1
+      template:
+        spec:
+          containers:
+          - image: docker.io/kubeflow/mpi-pi
+            name: mpi-launcher
+            securityContext:
+              runAsUser: 1000
+            command:
+            - mpirun
+            args:
+            - -np
+            - "2"
+            - /home/mpiuser/pi
+            resources:
+              limits:
+                cpu: 1
+                memory: 2Gi
+    Worker:
+      replicas: 2
+      template:
+        spec:
+          containers:
+          - image: docker.io/kubeflow/mpi-pi
+            name: mpi-worker
+            securityContext:
+              runAsUser: 1000
+              capabilities:
+                add:
+                - NET_BIND_SERVICE
+            command:
+            - /usr/sbin/sshd
+            args:
+            - -De
+            - -f
+            - /home/mpiuser/.sshd_config
+            resources:
+              limits:
+                cpu: 2
+                memory: 4Gi

examples/pi/sshd_config

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+PidFile /home/mpiuser/sshd.pid
+HostKey /home/mpiuser/.ssh/id_rsa