mongo.hcl

cell "mongodb" {
  name = "MongoDB Cell"
  version = "1.0"

  # Shameless borrow the term from hashicorp team. Or we use process group.
  molecule "mongos" {
    name = "MongoDB sharding"
    scalable = true        # Means user is able to scale the molecule up/down
    requires = ["config"]  # Define the molecule has be provisioned before this been provisioned

    var {
      # Default variable, when user doesn't specify port
      port = 11111
    }

    provision {
      driver = "docker"      # Or ansible, join/exec

      # Docker image
      image = "mongo"
      version = "3.2.1"

      # Support jinja2 template
      args = "mongos --configdb configReplSet/{{ config.endpoints|join(',') }}"

      env {
        PORT = "{{ this.port }}"
      }
    }
  }

  molecule "config" {
    name = "MongoDB config server"
    scalable = true
    vm-affinity = anti           # or affinity, tell the scheduler to put the same instance of molecues on the same vm or not.
    volume-affinity = unique     # unique means Use a volume exclusively

    var {
      # Default variable, when user doesn't specify port
      port = 27017
    }

    provision {
      driver = "docker"

      # Docker image
      image = "mongo"
      version = "3.2.1"

      args = "mongod --configsvr --replSet configReplSet --port {{ this.port }} --dbpath {{ this.volume }}"

      env {
      }

      # Post config runs inside of the docker task as 'docker exec'
      post_interval = "10s"  # Wait 10s to run post config command
      post_provision = <<-EOF
        mongo localhost --eval '
        rs.initiate( {
          _id: "configReplSet",
          configsvr: true,
          members: [
             <% for endpoint in this.endpoints %}
               { _id: id, host: "{{{ endpoint }}}" },
             <% endfor %>
          ]
        })
        '
      EOF
    }
  }

  molecule "shard" {
    name = "MongoDB replica_set as a shard"

    var {
      # Default variable, when user doesn't specify port
      port = 27017
    }


    config {
      driver = "docker"

      # Cell name
      image = "mongo"
      version = "3.2.1"

      args = "mongod --replSet rs0"

      env {
      }

      # Post config runs inside of the docker task as 'docker exec'
      post_interval = "10s"  # Wait 10s to run post config command
      post_config = <<-EOF
        mongo localhost --eval '
        rs.initiate();
        rs.add( {{ this.host }} );
        '
      EOF
    }
  }
}

mongo_provision.json

{
  "cell": "mongodb",
  "version": "1.0",
  "molecules": {
    "mongos": {
      "count": 3
    },
    "shard": {
      "count": 3,
      "spec": {
        "replica": 3,
        "subnet": "xx"
      }
    },
    "config": {
      "count": 3
    }
  },

  "provider": {
    "_comment": "What's the volume and network story? Allow user to specify?",

    "driver": "aws",
    "spec": {
      "region": "us",
      "datacentor": ["us-west-1"],
      "type": "m2.xlarge"
    }
  }
}