Add terraform version requirement and docs

Author: barryw

README.md

@@ -9,3 +9,58 @@
 
 #### Introduction
 
+This is a Terraform module for bringing up a fully-formed Zookeeper ensemble. It has the following features:
+
+- Forces an odd number of nodes for quorum.
+- Nodes are auto provisioning and auto healing. They will come up and cluster automatically.
+- Data and log volumes are separate.
+- CPU, memory, network and disk metrics are sent to CloudWatch metrics.
+- Zookeeper logs are sent to CloudWatch logs.
+
+#### Usage
+
+```hcl
+module "zookeeper" {
+  source = "github.com/barryw/terraform-aws-zookeeper"
+
+  # If empty, no keypair will be assigned to instances
+  keypair_name              = var.keypair
+  vpc_id                    = var.vpc_id
+  # Zookeeper instance subnets. Should be private
+  zookeeper_subnets         = [var.private_subnet1, var.private_subnet2]
+  # defaults to false
+  create_bastion            = true
+  bastion_subnet            = [var.public_subnet1]
+  bastion_ingress_cidrs     = ["0.0.0.0/0"]
+  zookeeper_version         = "3.7.0"
+  # Add any custom tags to include on created resources
+  tags                      = {}
+  # Gets added to the beginning of resource names
+  name_prefix               = "my-zookeeper"
+  # Must be odd
+  cluster_size              = 3
+  instance_type             = "m4.large"
+  root_volume_size          = 32
+  data_volume_type          = "gp2"
+  data_volume_size          = 10
+  log_volume_type           = "gp2"
+  log_volume_size           = 10
+  # Specify a zone to create records on
+  route53_zone              = ""
+  # Specify the security group id of the groups to allow connections to ZK. If not specified, use the VPC's CIDR
+  client_security_group_id  = ""
+  # The namespace to use for CloudWatch metrics
+  cloudwatch_namespace      = "CWAgent"
+  zookeeper_config = {
+    clientPort = 2181,
+    syncLimit  = 5,
+    initLimit  = 10,
+    tickTime   = 2000,
+    zkHeap     = 4096
+  }
+}
+```
+
+#### License
+
+This module is licensed under the MIT license: https://opensource.org/licenses/MIT

main.tf

@@ -1,3 +1,7 @@
+terraform {
+  required_version = ">=0.13.0"
+}
+
 locals {
   prefix   = var.name_prefix == "" ? "" : "${var.name_prefix}-"
   asg_arns = jsonencode([for arn in aws_autoscaling_group.zookeeper.*.arn : arn])