Dustul

Introduction

Dustul is a Dust-based an alternative to consul-template. It allows you to subscribe to changes within Consul and render templates (using Dust template syntax) to disk as they occur. After rendering occurs, one or more commands can also be executed (e.g. service nginx restart, etc...).

Getting Started

Dustul is a command-line utility. As such, it should be installed globally via npm i -g dustul. Afterwards, getting started is a simple matter of creating a configuration file, as shown below.

Take note:

• The file should export an array of configuration objects, allowing you to define one or more templates to be rendered.
• Dustul relies on npm's consul package for interactions with Consul. For more information on the symantics that are used for defining subscriptions, see that project's documentation.

// config.js
module.exports = [
    {
        'config': {
        	/**
        	 * Consul options
        	 */
            'consul': {
                'host': '192.168.50.2',
                'port': 8500
            }
        },
        /**
         * The context object to be passed to Dust as Consul changes occur.
         * Here you can define context helpers, pre-defined data, etc...
         */
        'context': {
        },
        /**
         * Consul subscriptions are defined here. As changes occur, incoming data is processed
         * and assigned to the context object using the associated key. For example, our cities
         * subscription will be processed and stored at context.cities.
         */
        'watch': {
        	/**
        	 * Subscribe to changes within Consul's key / value store.
        	 */
            'cities': {
                'method': 'kv.get',
                'options': {
                    'key': 'config/env-app/cities',
                    'recurse': false
                },
                /**
                 * Optional callback. Allows you to manipulate incoming data before it is stored
                 * within the context object.
                 */
                'cb': (data) => {
                    return JSON.parse(data.Value);
                }
            },
            /**
             * Subscribe to a list of available Consul nodes.
             */
            'nodes': {
                'method': 'catalog.node.list'
            },
            /**
             * Subscribe to a list of available Consul services.
             */
            'services': {
                'method': 'catalog.service.list'
            },
            /**
             * Subscribe to a list of available Consul nodes for a specific service.
             */
            'consul_nodes': {
                'method': 'catalog.service.nodes',
                'options': {
                    'service': 'consul'
                }
            }
        },
        /**
         * This function is called just before Dust rendering occurs. Here you
         * can make final modifications to your context object.
         */
        'beforeRender': (consul, context) => {
            context.date = new Date();
        },
        /**
         * Whether or not to trim whitespace from the beginning and end of the rendered template
         * before saving to disk. Default: false
         */
        'trim': true,
        /**
         * An array of commands (and corresponding arguments) to be executed after rendering
         * has completed. Values for command, args, and options are passed to Node's process.spawn
         * method. Commands are run in order as a sequence.
         */
        'commands': [
            {
                'command': 'service',
                'args': ['nginx', 'restart'],
                'options': {}
            }
        ],
        /**
         * The path at which the rendered template will be saved. Relative paths
         * are considered relative to the location at which Dustul is executed. You'd be better
         * off sticking with absolute paths.
         */
        'destination': '/etc/nginx/sites-enabled/my-site.conf',
        /**
         * The Dust template
         */
        'template': `
            upstream my_upstream {
                {#consul_nodes}
                    server {Address};
                {/consul_nodes}
            }
            
            server {
                listen 80;
                location / {
                    proxy_pass http://my_upstream;
                }
            }
        `
    }
];

Next, call Dustul and provide it with the path to your configuration file, as shown below.

$ dustul subscribe -c ./config.js

Limitations & Desired Contributions

At the moment, Dustul only allows you to subscribe to changes within Consul's key value store. Short-term plans including adding support for subscribing to service and node changes, as well.

Related Resources

• Consul
• consul-template
• Dust
• node-consul