nepho-example

This is an example cloudlet for nepho that demonstrates key concepts and structure.

Key Concepts

1. All Nepho cloudlets contain a cloudlet.yaml metadata file, one or more blueprints, additional data, and implementations of three required hooks: bootstrap, configure, and deploy (any or all of which can be a no-op).
2. Blueprints are YAML documents that provide a list of input parameters that the user will be prompted to enter, and which will then be passed to the provider plugin. A combination of inputted parameters and a blueprint are called a scenario, and are used to launch a running instance of the environment, called a stack.
3. The format of the data directory and the accepted parameters are specified by the provider plugin itself. For example, the vagrant provider plugin requires only that a valid Vagrantfile be present in a directory under data named the same as the blueprint.

Hooks

bootstrap
The bootstrap hook is the first hook run, and is meant to be run only once, to bootstrap an instance to a level where the configure hook can be run. In this example cloudlet, the bootstrap hook is a very comprehensive implementation that sets up a stock Debian, Ubuntu, Amazon Linux, Red Hat, or CentOS instance with required packages and configuration to run Puppet. The bootstrap hook should do no more and no less than prepare an instance for the configure hook.

configure
This hook is typically used to launch a configuration management (CM) tool, in this case Puppet. The configure hook should be idempotent, meaning it can be run multiple times and always bring the instance to a desired state, without causing negative effects. In this example the Puppet process is run twice, which is often good practice due to dependencies and timing errors that can occur on a first run, especially with complex configurations.

deploy
The final hook is deploy, which is used to prepare an application/service. Examples of the use of the deploy hook include downloading and installing executable code, populating a database, joining a cluster, or simply printing instructions for a user to perform these steps manually (or with an existing tool). The deploy hook should be sufficiently robust that it can be run multiple times without causing harm. In this example, the deploy hook is a no-op.

Limitations

• Currently this cloudlet only supports the "vagrant" nepho provider plugin, in the future it may be expanded to support other provider backends.
• Running the complete bootstrap process in this example cloudlet can take a long time. For distributed cloudlets, the current recommendation is to provide a base AMI, Vagrant box, or equivalent that has been pre-bootstrapped. The example bootstrap hook in this cloudlet automatically checks to see if it has already been run before continuing.