7.3 Composition

Instead of instantiating the Chart two times manually by hand, we can also define a composition of two Charts in a single Chart. In other 2words we create a new Helm Chart and add the Chart we just wrote twice as a dependency to the chart.

In Helm we can make a composition of already existing Charts and own templates and define it as a new Chart. This is a very common use case if we mix self created resources with own templated resources.

How do we achieve this? Maybe first a bit of theoretical input:

We can declare dependencies in the Chart.yaml like the following:

# Chart.yaml
dependencies:
- name: memcached
  version: "3.2.1"
  repository: "https://another.example.com/charts"
- name: nginx
  version: "1.2.3"
  repository: "file://../dependency_chart/nginx"
- name: helm-basic-chart
  version: "0.1.0"
  alias: consumer

In the example above we can see the dependency block of the Chart.yaml. We define three dependencies in the Chart and add memcached, nginx and helm-basic-chart as a dependency. As you can see the syntax varies a bit, let’s check it for a second:

• name: The ’name’ should be the name of a chart, where that name must match the name in that chart’s ‘Chart.yaml’ file
• version: The ‘version’ field should contain a semantic version or version range
• repository: The ‘repository’ URL should point to a Chart Repository or to a Chart in your local filesystem
• alias: The ‘alias’ of a dependency (this is very handy to import the same Chart twice)

If we add a dependency without the repository defined, Helm will try to find the defined dependency in either your added repositories or the /charts directory in your Chart’s directory.

So let’s get some work done!

Task 7.3.1 Create a new Chart

Create a new Chart parent and empty the templates folder, since we don’t need any additional templates in the Chart other than the dependencies.

helm create parent
rm -rf parent/templates/*

Task 7.3.2 Copy the dependecies

Duplicate the Chart we created in the section before. Copy the duplicated Chart from the section before into your new Chart’s /charts directory.

Your new Chart’s structure should look like this:

$ tree parent/
parent/
├── Chart.yaml
├── charts
│   └── helm-basic-chart
│       ├── Chart.yaml
│       ├── templates
│       │   ├── _helpers.tpl
│       │   ├── deployment.yaml
│       │   ├── ingress.yaml
│       │   ├── service.yaml
│       │   └── tests
│       │       └── test-connection.yaml
│       └── values.yaml
├── templates
└── values.yaml

Task 7.3.3 Add the chart as dependency

Add two new dependencies to your parent Chart’s dependencies with the aliases producer and consumer. Since we have the helm-basic-chart (or the name you chose in the dependency) in the local /charts directory, we don’t need to add any repository in the dependency definition.

# Chart.yaml

apiVersion: v2
name: parent
description: A Helm chart for Kubernetes
type: application
version: 0.1.0
appVersion: "1.16.0"
dependencies:
- name: helm-basic-chart
  version: "0.1.0"
  alias: producer
- name: helm-basic-chart
  version: "0.1.0"
  alias: consumer

Task 7.3.4 Configure the values

When we add dependencies to your Helm Charts we can configure them in the parent’s values.yaml. We can override configuration of dependencies in a parent chart by adding configuration in the values.yaml prefixed by the dependencies name or alias. For example if we have a dependency nginx in your Chart.yaml we can override the configuration of the nginx’s url property like the following:

# parent/values.yaml 
nginx:
    url: samplehost

It is your task to configure the two dependencies so they will work just as they worked before!

# parent/values.yaml

consumer:
  # Consumer's config

producer:
  # Producer's config

consumer:
  host: consumer-<username>.training.cluster.acend.ch
  image:
    name: quay.io/puzzle/quarkus-techlab-data-consumer
    tag: latest
  logLevel: INFO
  resources:
    limits:
      cpu: '1'
      memory: 750Mi
    requests:
      cpu: 50m
      memory: 100Mi
  serviceName: consumer
  producerServiceName: producer-helm-basic-chart-producer

producer:
  host: producer-<username>.training.cluster.acend.ch
  image:
    name: quay.io/puzzle/quarkus-techlab-data-producer
    tag: latest
  logLevel: INFO
  resources:
    limits:
      cpu: '1'
      memory: 750Mi
    requests:
      cpu: 50m
      memory: 100Mi
  serviceName: producer

Task 7.3.5 Install the release

Install a Helm Chart release myrelease and verify if the two services are running correctly!

helm upgrade -i myrelease parent/.

Task 7.3.5 Verify the release

curl -kL $(kubectl get ingress <releasename>-consumer --template="{{(index .spec.rules 0).host}}")/data
{"data":0.4145158804475594}

Task 7.3.6 Clean up

Congratulations! You succeeded in the Chapter and the only thing left is to do some cleanup afterwards!

Remove all the installed objects installed during the chapter!

helm uninstall myrelease