cascading-service-config

dry configuration for a multi-service system

npm install cascading-service-config
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Cascading Service Config

is a format for a versatile configuration file that configures more than one http service in a single system.

What does it do?

  • Extract a configuration for a single service from a global configuration file.
  • Supply access points to each of the other services in the system, that are configured in the global configuration file.
  • Inherit configurations of modules that are shared between services.

Install

npm install cascading-service-config

Example

Lets say we have an example config with two services and an authentication module (which requires a config) that both services depend on, as well as some shared settings. Our config might look like this:

var configSource = {
  logmethod: "syslog", // a shared setting
  auth: {
    cookie: "authKey",
    storage: {
      type: "redis",
      location: "localhost:6789"
    }
  },
  service1: {
    port: 8402,
    logmethod: "loggly",
    wibblewobbles: true
  },
  service2: {
    port: 8403
  }
}

Now we can give this to CSC, as well as a domain - the domain is just the name of the service which is currently reading the config.

var config = require('cascading-service-config')(configSource, 'service1');

Now we have our config object. The properties which you have access to look like this (but this is different to what you'll get if you console.log it, as we are making using of prototypical inheritance):

{ 
  logmethod: "loggly", // note that we overrode the shared setting here
  auth: { 
    service1: "http://localhost:8402",
    service2: "http://localhost:8403",
    logmethod: "syslog",
    auth: [circular reference],
    cookie: "authKey", 
    storage: { type: "redis", location: "localhost:6789" } 
  },
  service1: "http://localhost:8402",
  service2: "http://localhost:8403",
  wibblewobbles: true,
  port: 8402
}

So what's happening here?

Because we specified service1 as our domain, that's is our top-level config object. All properties in the service1 object of the config source are passed verbatim to the final config.

However, under this, we have two objects which we inherit.

  1. { service1: "http://localhost:8402", service2: "http://localhost:8403" } - CSC looks through each of the objects on the root level of the config. If an object has a port setting, it is assumed to be a service. This object consists of assembled access points for each of the other services in your domain, so that they're easily accessible on your config.
  2. The original config. This is the base prototype.

Also note that each other object on the root config also gains the same prototype chain, so in our example, auth also gained the service locations.

In our example, the prototype chain looks something like this:

      { wibblewobbles: true, logmethod: "loggly", port: 8402 }
//                          inherits...
  { service1: "http://localhost:8402", service2: "http://localhost:8403" }
//                          inherits...
  { auth: { ... }, logmethod: "syslog", service1: { ... }, service2: { ... } }

My other services aren't running on http or localhost

No problem! There's two special config options you can use to configure this: internalServiceHostname and internalServiceProtocol. You can configure this globally or per-object. In our example, we could set:

{
  logmethod: "syslog"
  internalServiceHostname: "amazing.service.com",
  internalServiceProtocol: "https",
  ...

Which, in our final config, would result in...

console.log(config.service2);
// -> 'https://amazing.service.com:8403'

But what if service1 is running on http, not https? Well, we can override the root internalServiceProtocol in service1's config:

  ...
  service1: {
    internalServiceProtocol: "http",
    port: 8402,
    ...

Resulting in...

console.log(config.service1);
// -> 'http://amazing.service.com:8402'
console.log(config.service2);
// -> 'https://amazing.service.com:8403'

Can I access the config of other services?

It's possible, but very much discouraged (as you'll see from the syntax). Config formats change, and depending upon another service's config format is usually a pretty bad idea.

However, if you absolutely must do it, there are two ways.

You could access the source config object by traversing the prototype chain:

console.log(config.__proto__.__proto__.service2.port);
// -> 8403

Or you could just call CSC again and specify the domain of the other service:

var service2config = require('cascading-service-config')(configSource, 'service2');
console.log(service2config.port);
// -> 8403

csc(configSourceObject, [domain])

Reads a cascading service config file and returns a config for the given domain. If the domain does not exist, the root config is returned.

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