Add an example for running rethinkdb cluster on k8s

examples/rethinkdb/image/Dockerfile

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+FROM rethinkdb:1.16.0
+
+MAINTAINER BinZhao <wo@zhaob.in>
+
+RUN apt-get update && \
+    apt-get install -yq curl && \
+    rm -rf /var/cache/apt/* && rm -rf /var/lib/apt/lists/* && \
+    curl -L http://stedolan.github.io/jq/download/linux64/jq > /usr/bin/jq && \
+    chmod u+x /usr/bin/jq
+
+COPY ./run.sh /usr/bin/run.sh
+RUN chmod u+x /usr/bin/run.sh
+
+CMD ["/usr/bin/run.sh"]

examples/rethinkdb/image/run.sh

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+#!/bin/bash
+
+set -o pipefail
+
+IP=""
+if [[ -n "${KUBERNETES_RO_SERVICE_HOST}" ]]; then
+
+  : ${NAMESPACE:=rethinkdb}
+  # try to pick up first different ip from endpoints
+  MYHOST=$(ip addr | grep 'state UP' -A2 | tail -n1 | awk '{print $2}' | cut -f1  -d'/')
+  URL="${KUBERNETES_RO_SERVICE_HOST}/api/v1beta1/endpoints/rethinkdb-driver?namespace=${NAMESPACE}"
+  IP=$(curl -s ${URL} | jq -s -r --arg h "${MYHOST}" '.[0].endpoints | [ .[]? | split(":") ] | map(select(.[0] != $h)) | .[0][0]') || exit 1
+  [[ "${IP}" == null ]] && IP=""
+fi
+
+if [[ -n "${IP}" ]]; then
+  ENDPOINT="${IP}:29015"
+  echo "Join to ${ENDPOINT}"
+  exec rethinkdb --bind all  --join ${ENDPOINT}
+else
+  echo "Start single instance"
+  exec rethinkdb --bind all
+fi