myriad

Configuration as a Service (CaaS) "having innumerable aspects or elements"

Build Status

	Status of last build
Mono
Windows

Why?

Inspired by this article: https://www.devopsonwindows.com/implement-context-aware-key-value-store/

Context-aware key-value stores (CA-KVS) can be critical to operational stability in environments where there may be a high cost to deploying software and managing multiple system components with shared configuration. CA-KVS seeks to decrease overall system complexity by centralizing all configuration in one place. Applications provide a context and key name and the service provides a value specific to that context.

Terminology

• Context-aware key-value stores (CA-KVS or store): Repository where configuration data is stored
• Dimension: Defines a scope of context. This is a named value that describes a single extent of the configuration space, e.g. "Environment" or "Application".
• Measure: Defines a value for a dimension; e.g. Dimension(Environment) = "Production"
• Cluster: Defines a set of measures and value; e.g. Dimension(Environment) = "Production" and Dimension(Application) = "MyApp" have the value "foo".
• Property: Defines a key and ordered list of clusters. Clusters are ordered by weight as described below.
• Context: Defines a point in time (as of) and set of measures. The context is matched against a property in order to extract a value from one of the clusters. Note that any or none of the clusters could match a context and only the first is returned when resolving a property value.

Generally, context defines the degrees of freedom over which configuration key-values are needed. The ordered list of all dimensions defines the supported context for a given store. In a single application space, for example, there may only be a distinction between environments, like "production" and "development". For multiple components, another dimension like "Application" may be required.

Approach

1. Take dimensions and determine weights based on ordering

   • Dimensions are weighted in reverse order, e.g. Instance, Application, Location, Environment
   • Weights are computed for each level as 2^n where n is the level, e.g. Environment=1, Location=2, Application=4, Instance=8
   • When no dimensions are specified, the key gets a weight of zero (effectively the value's default)

2. For a given property, apply the weighted ordering to its set of clusters, sorting from greatest to least

   Environment (1)	Location (2)	Application (4)	Instance (8)	Total Weight	Property Value
   x	x	-	x	11	apple
   x	-	-	x	9	pear
   -	-	-	x	8	pecan
   -	-	x	-	4	peach
   -	x	-	-	2	strawberry
   x	-	-	-	1	apricot
   -	-	-	-	0	pumpkin

3. Lookups are accomplished by, for a given key, matching the provided context against the set for the first positive match; matches must match over all dimensions to be considered equal

System Details

Platforms

Myriad runs on Windows and Linux under Mono and can be hosted in Amazon Web Services. Support for Azure is planned.

Persistence

Myriad supports the following persistent stores:

• MySql
• Redis (in progress)
• Microsoft SQL Server (planned)