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Lab: Externalizing Application Configuration

Background: Application Configuration with ConfigMaps

Most applications require configuration using environment variables, configuration files and command line arguments. These configuration artifacts should be externalized form the application and the docker image content in order to keep the image portable across environments.

In previous labs, the nationalparks application was configured with database credentials using environment variables. While environment variables is a useful way to configure applications, it is difficult to manage hundreds of environment variables which are scattered across various containers in a project. Fortunately, there is a convenient and platform-independent mechanism in OpenShift to configure applications, which is called ConfigMap.

The ConfigMap object in OpenShift provides mechanisms to provide configuration data to the application container while keeping the application images both portable across environments and independent of OpenShift Container Platform. A ConfigMap can be used to store key-value properties, configuration files, JSON blobs and alike.

In this lab, you will replace the environment variables provided in the previous labs and use a ConfigMap instead to configure the nationalparks application.

Exercise: Create a ConfigMap

You can create a ConfigMap by pointing at a file containing the application configuration. Download this properties file to your local machine which contains the database credentials:

http://gitlab-ce-workshop-infra.{{ROUTER_ADDRESS}}/{{GITLAB_USER}}/nationalparks/raw/{{NATIONALPARKS_VERSION}}/ose3/application-dev.properties
Note
 Verify that the contents of the file are correct. If you have downladed the file with Internet Explorer it might contain incorrect chars or different charset. Try to use "Google Chrome", "Firefox" or "curl".

Create a ConfigMap using the following command in the {{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}} project:

$ oc create configmap nationalparks --from-file=application.properties=./application-dev.properties

The --from-file option specifies a key-value pair with the key used as the file name that is provided to the application and value as the content of the file. In the above command, the content of application-dev.properties file will be provided to the application container as a properties file called application.properties

List and verify that the ConfigMap is created successfully containing the database credentials:

$ oc describe configmap nationalparks

Name:		nationalparks
Namespace:	demo
Labels:		<none>
Annotations:	<none>

Data
====
application.properties:	123 bytes

You can review the content of the ConfigMap using the oc get command:

$ oc get configmap nationalparks -o yaml

apiVersion: v1
data:
  application.properties: |
    # NationalParks MongoDB
    mongodb.server.host=mongodb
    mongodb.user=mongodb
    mongodb.password=mongodb
    mongodb.database=mongodb
kind: ConfigMap
metadata:
  creationTimestamp: 2016-11-16T09:17:02Z
  name: nationalparks
  namespace: {{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}
  resourceVersion: "8421"
  selfLink: /api/v1/namespaces/demo/configmaps/nationalparks
  uid: 6f4536cf-abdd-11e6-9282-525400c3c0db

Exercise: Wire the ConfigMap inside nationalparks Container

Configuration data can be consumed in pods in a variety of ways. A ConfigMap can be used to:

  • Populate the value of environment variables

  • Set command-line arguments in a container

  • Populate configuration files in a volume

The nationalparks Spring Boot application can be configured through a properties file called application.properties which should reside in a specific location in the container filesystem. Using the following command to mount the ConfigMap inside the nationalparks pod:

$ oc set volumes dc/nationalparks --add -m /deployments/config --configmap-name=nationalparks

The above command makes the content of the configmap ConfigMap, which you created from a file, called application.properties, available in the /opt/openshift/config directory. The nationalparks DeploymentConfiguration detects the configuration change, and automatically deploys the Pod with the new configuration.

Also, as we have configured nationalparks through ConfigMap, you can remove the database environment variables set in the previous labs:

$ oc env dc/nationalparks MONGODB_USER- MONGODB_PASSWORD- MONGODB_DATABASE- MONGODB_SERVER_HOST-

You have now externalized nationalparks configuration. Visit the nationalparks web service to very the database connection is working correctly.:

http://nationalparks-{{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}.{{ROUTER_ADDRESS}}/ws/data/all/

If you check the new Pod’s logs once it comes up, you should see no errors.