148422597X Kubernetes Management Design Patterns [Vohra 2017-01-29] {E559F6BB}

CHAPTER 11
Using ConfigMaps
In Chapter 10 and some earlier chapters, we used the spec: containers: env: field to specify an
environment variable for the Docker image mysql for the MySQL database.
Problem
Consider the use case that some environment variables such as username and password for a database are
to be used in multiple replication controller or pod definition files. The username and password value would
need to be specified in each of the definition files. And if the username and password were to change, all the
definition files would need to be updated as well, which could be very tedious. Alternatively, variable values
could be supplied to kubectl when a command is run, which involves specifying command-line flags each
time the command is run.
Solution
The ConfigMap management pattern is a map of configuration properties that can be used in definition
files for pods, replication controllers, and other Kubernetes objects to configure environment variables,
command arguments, and configuration files such as key-value pairs in volumes, to list a few example
uses. A single ConfigMap may package multiple configuration properties as key/value pairs. By creating
ConfigMaps, you specify the configuration properties in a single configuration map, which can be updated
as required without having to update each of the definition files in which the ConfigMap is used. Decoupling
the containers from the configuration data provides portability of the applications running in the containers.
Overview
A ConfigMap definition file schema provides for the following (Table 11-1) fields.
Table 11-1. ConfigMap Fields
Field
kind
apiVersion
metadata
data
Description
The resource type. Must be set to ConfigMap.
Version of the schema.
Metadata such as name, labels, namespace and annotations.
Configuration data as key/value pairs.
© Deepak Vohra 2017
D. Vohra, Kubernetes Management Design Patterns, DOI 10.1007/978-1-4842-2598-1_11
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