container.training/slides/exercises/appconfig-details.md

Exercise — Application Configuration

• We want to configure an application with a ConfigMap

• We will use the "rainbow" example shown previously

  (HAProxy load balancing traffic to services in multiple namespaces)

• We won't provide the HAProxy configuration file

• Instead, we will provide a list of namespaces

  (e.g. as a space-delimited list in a ConfigMap)

• Our Pod should generate the HAProxy configuration using the ConfigMap

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Setup

• Let's say that we have the "rainbow" app deployed:

  kubectl apply -f ~/container.training/k8s/rainbow.yaml
  

• And a ConfigMap like the following one:

  kubectl create configmap rainbow --from-literal=namespaces="blue green"
  

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Goal 1

• We want a Deployment and a Service called rainbow

• The rainbow Service should load balance across Namespaces blue and green

  (i.e. to the Services called color in both these Namespaces)

• We want to be able to update the configuration:

  • update the ConfigMap to put blue green red

  • what should we do so that HAproxy picks up the change?

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Goal 2

• Check what happens if we specify a backend that doesn't exist

  (e.g. add purple to the list of namespaces)

• If we specify invalid backends to HAProxy, it won't start!

• Implement a workaround among these two:

  • remove invalid backends from the list before starting HAProxy

  • wait until all backends are valid before starting HAProxy

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Goal 3

• We'd like HAProxy to pick up ConfigMap updates automatically

• How can we do that?

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Hints

• Check the following slides if you need help!

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• We want to generate the HAProxy configuration in an initContainer

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• The namespaces entry of the rainbow ConfigMap should be exposed to the initContainer

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• The HAProxy configuration should be in a volume shared with HAProxy