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Apache ZooKeeper

Apache ZooKeeper

Deploy an Apache ZooKeeper cluster. Supports automatic bootstrap, Exhibitor, zero-downtime rolling deployment, and auto healing.

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Terraform Version

ZooKeeper

This repo contains modules for deploying and managing Apache ZooKeeper along with Exhibitor.

The main modules are:

  • zookeeper-cluster: A Terraform module to run a cluster of ZooKeeper nodes with ENIs and EBS Volumes attached, zero-downtime deployment, and auto-recovery of failed nodes.

  • install-zookeeper: Install Apache ZooKeeper.

  • install-exhibitor: Install Exhibitor, a process supervisor for ZooKeeper.

  • run-exhibitor: Start Exhibitor, which, in turn, will start ZooKeeper.

The supporting modules are:

Click on each module above to see its documentation.

Getting started

Head over to the examples folder for working example code.

What is ZooKeeper?

Apache ZooKeeper is an open source, distributed, hierarchical, key-value store. It implements a distributed consensus protocol, which makes it a useful primitive in other distributed systems (e.g., Kafka, Mesos, Neo4j) as a way to do leader election, synchronization, coordination, locking, naming registry, and so on.

What is Exhibitor?

Exhibitor is a supervisor system for ZooKeeper that provides a number of features, including starting the ZooKeeper process, restarting the process if it fails, performing periodic cleanup of ZooKeeper's log directory, and offering a GUI for viewing ZooKeeper nodes.

What is a Gruntwork module?

At Gruntwork, we've taken the thousands of hours we spent building infrastructure on AWS and condensed all that experience and code into pre-built packages or modules. Each module is a battle-tested, best-practices definition of a piece of infrastructure, such as a VPC, ECS cluster, or an Auto Scaling Group. Modules are versioned using Semantic Versioning to allow Gruntwork clients to keep up to date with the latest infrastructure best practices in a systematic way.

How do you use a module?

Most of our modules contain either:

  1. Terraform code
  2. Scripts & binaries

Using a Terraform Module

To use a module in your Terraform templates, create a module resource and set its source field to the Git URL of this repo. You should also set the ref parameter so you're fixed to a specific version of this repo, as the master branch may have backwards incompatible changes (see module sources).

For example, to use v1.0.8 of the standalone-server module, you would add the following:

module "ecs_cluster" {
  source = "git::git@github.com:gruntwork-io/module-server.git//modules/standalone-server?ref=v1.0.8"

  // set the parameters for the standalone-server module
}

Note: the double slash (//) is intentional and required. It's part of Terraform's Git syntax (see module sources).

See the module's documentation and vars.tf file for all the parameters you can set. Run terraform get -update to pull the latest version of this module from this repo before running the standard terraform plan and terraform apply commands.

Using scripts & binaries

You can install the scripts and binaries in the modules folder of any repo using the Gruntwork Installer. For example, if the scripts you want to install are in the modules/ecs-scripts folder of the https://github.com/gruntwork-io/module-ecs repo, you could install them as follows:

gruntwork-install --module-name "ecs-scripts" --repo "https://github.com/gruntwork-io/module-ecs" --tag "0.0.1"

See the docs for each script & binary for detailed instructions on how to use them.

Developing a module

Versioning

We are following the principles of Semantic Versioning. During initial development, the major version is to 0 (e.g., 0.x.y), which indicates the code does not yet have a stable API. Once we hit 1.0.0, we will follow these rules:

  1. Increment the patch version for backwards-compatible bug fixes (e.g., v1.0.8 -> v1.0.9).
  2. Increment the minor version for new features that are backwards-compatible (e.g., v1.0.8 -> 1.1.0).
  3. Increment the major version for any backwards-incompatible changes (e.g. 1.0.8 -> 2.0.0).

The version is defined using Git tags. Use GitHub to create a release, which will have the effect of adding a git tag.

Tests

See the test folder for details.

License

Please see LICENSE.txt for details on how the code in this repo is licensed.

Questions? Ask away.

We're here to talk about our services, answer any questions, give advice, or just to chat.

Ready to hand off the Gruntwork?