mongo-replicaset-priority.js

var expectedReplicaSetMembers = [
  {
    _id: 0,
    host: 'api-mongo-1:27017'
  },
  {
    _id: 1,
    host: 'api-mongo-2:27017'
  },
  {
    _id: 2,
    host: 'api-mongo-3:27017'
  }
]

var actualReplicaSetConfig = rs.conf()
var replicaSetChangesMade = false

for (var i = 0; i < expectedReplicaSetMembers.length; i++) {
  printjson(expectedReplicaSetMembers[i]);
  expectedMember = expectedReplicaSetMembers[i];
  thisMember = actualReplicaSetConfig.members.filter(function (value) {
    return value.host === expectedMember.host
  })[0];
  printjson(thisMember);
  if expectedMember.priority {
    if expectedMember.priority !== thisMember.priority
  }
}

if replicaSetChangesMade {
  rs.reconfig(actualReplicaSetConfig)
}

template.erb

var expectedReplicaSetMembers = [
  <% for thing in things %>
  {
    _id: 0,
    host: '$HOSTNAME:27017'
    <% if priority != 1 %>
    priority: $PRIORITY
    <% endif %>
  },
  <% endfor %>
]