Last modified November 29, 2024

App configuration reference

The Giant Swarm’s app platform allows you to easily install apps across your entire fleet of clusters. The platform fully support helm as a general tool to deploy your applications as well as the official Giant Swarm app catalog.

The apps are packaged as helm charts. Those charts rely on values to be set in order to fill in placeholders in templates. By configuring your app you set the values that become available to the templates when they’re deployed.

Configuration levels

There are three levels of configuration:

1. Catalog: Configuration provided by the publisher of the App catalog.
2. Cluster: Configuration provided by the cluster admin.
3. User: Configuration provided by the user installing an App.

Each level overrides the previous one. As a user you aren’t expected to edit configuration at the catalog or cluster level. However, user level configuration can override both catalog and cluster level configuration.

Besides, there is a list of extra configuration layers with special priority field that you can control the level around which they will be applied to the core configurations. Head to the extra configuration layers section to learn more about them.

Each level of configuration - same applies to extra configuration layers - has two types of values that you can provide:

1. Configuration values: Configuration provided as a ConfigMap resource.
2. Secret values: Configuration and credentials provided as a Secret resource.

All values are gathered together and merged into the final values object that will become available to the chart template.

Values are merged in the following order:

1. Catalog configuration values
2. Catalog secret values
3. Cluster configuration values
4. Cluster secret values
5. User configuration values
6. User secret values

If no value is provided then the default in the chart’s values file (values.yaml) is used.

Note: Attempting to change configuration at any other level is risky because your changes might be overwritten by an operator.

General notes about app configuration

When using app platform, it’s important to remember, that most of the configuration changes in kubernetes are asynchronous and only eventually consistent. This also applies to App resources and theirs configuration. To better understand that, let’s use an example where you update the application version in the App resource from version v1.0.0 to v2.0.0 and the same time you update the ConfigMap referenced by the App resource (let’s call the ConfigMap before the change configMap v1 and after the change configMap v2).

As these changes are completely independent for kubernetes, the following scenario is possible:

• The App resource is in version v1.0.0 and ConfigMap is in v1
• Both App resource and the referenced ConfigMap are edited
• The application’s version change is already processed, so the application runs in v2.0.0 with a ConfigMap v1
• After some time, the ConfigMap change is processed, the application will now run in v2.0.0 with a ConfigMap in version v2

Obviously, it can also happen that the ConfigMap is updated first, then the application version. The time between one and the other change being processed is usually very short, still it’s important to understand, that such situations might and will happen.

Example of values merging

Given a chart with a values.yaml that contains the following content:

colors:
  background: "black"
  foreground: "white"

  # This is a secret, so we leave it blank in the Chart's values.yaml since
  # it's specific to the deployment and there is no sane default.
  secretColor: ""

Now you create an App resource that references a user level ConfigMap and a user level secret:

apiVersion: application.giantswarm.io/v1alpha1
kind: App
metadata:
  name: hello-world
  namespace: i5h93
spec:
  catalog: giantswarm-playground
  ...
  name: hello-world-app
  namespace: hello-world-app
  userConfig:
    configMap:
      name: hello-world-user-values
      namespace: i5h93
    secret:
      name: hello-world-user-secrets
      namespace: i5h93
  ...

The hello-world-user-values ConfigMap contains the following content:

apiVersion: v1
kind: configmap
metadata:
  name: hello-world-user-values
  namespace: i5h93
data:
  values: |
    colors:
      background: "red"    

The hello-world-user-secrets secret contains this:

apiVersion: v1
kind: secret
metadata:
  name: hello-world-user-secrets
  namespace: i5h93
data:
  values: "Y29sb3I6CiAgc2VjcmV0Q29sb3I6ICJibHVlIgo="

Note: when Base64 decoding the string .data.values field in the secret, you’ll get this:

colors:
  secretColor: "blue"

Then the resulting values applied to the helm chart will be:

colors:
  background: "red"
  foreground: "white"
  secretColor: "blue"

As you can see, we made an override for .colors.background, changing it from black to red, and set the .colors.secretColor value to blue using values from the secret.

You can use these values throughout your chart using the normal templating of helm charts:

# hello-world-app/helm/chart/hello-world/templates/colors-configmap.yaml
apiVersion: v1
kind: configmap
metadata:
  name: hello-world-configmap
  namespace: {{ .Release.Namespace }}
  labels:
    app: hello-world
data:
  background: {{.Values.colors.background}}
  foreground: {{.Values.colors.foreground}}

# hello-world-app/helm/chart/hello-world/templates/colors-secret.yaml
apiVersion: v1
kind: secret
metadata:
  name: hello-world-secret
  namespace: {{ .Release.Namespace }}
  labels:
    app: hello-world
data:
  secretColor: {{.Values.colors.secretColor | b64enc | quote}}

Note: If you uploaded your secret as individual plain values and want to use one of those values in an actual templated secret, then you have to base64 encode it to comply with how kubernetes stores secrets. Our API only encodes the entire secrets value string. It doesn’t individually encode each value.

How configuration values are stored

Configuration for apps are stored as ConfigMaps and Secrets, which are referenced by name and namespace in various spec fields of the App and Catalog custom resource.

Our operators act on those resources to ensure the actual state ends up looking like the desired state. More information is available in our general overview of the app platform.

Extra configuration layers

You can set a list of extra configuration layers via .spec.extraConfigs. For example:

spec:
  catalog: giantswarm-test
  extraConfigs:
    - name: hello-world-extra-values-pre-cluster
      namespace: i5h93
    - kind: secret
      name: hello-world-extra-secrets-pre-cluster
      namespace: i5h93
    - name: hello-world-extra-values-pre-user
      namespace: i5h93
      priority: 75
    - kind: secret
      name: hello-world-extra-secrets-post-user
      namespace: i5h93
      priority: 125

The name and namespace fields are required for each entry. However, note that it’s optional to set kind. It defaults to configMap. It’s also optional to set priority. It defaults to 25.

The three configuration levels all have an assigned priority value bound to them behind the scenes:

1. Catalog has priority 0.
2. Cluster has priority 50.
3. User has priority 100.

The priority field for spec.extraConfigs entries must be set to a numerical value between (inclusively) 1 and 150.

This extends the example of values merging section.

The base upon we merge all other layers is always the Catalog layer. That’s why it has priority set to 0 and you can only set priority value starting from 1.

Then for each kind (configMap, secret) we look up each entry and merge them in the following way:

1. The Catalog is the base.
2. All spec.extraConfigs entry with priority greater than the Catalog level and lower than or equal to the Cluster level are merged.
3. The Cluster level configurations are merged.
4. All spec.extraConfigs entry with priority greater than the Cluster level and lower than or equal to the User level are merged.
5. The User level configurations are merged.
6. All spec.extraConfigs entry with priority greater than the User level and lower than or equal to the maximum level of 150 are merged.

In case of multiple spec.extraConfigs entries with the same priority level, the order on the list is binding, with the item lower on the list being merged later (overriding those higher on the list).

Example of merging extra configuration

Let’s take the following example with just ConfigMaps to make it simple. The same merging algorithm applies for secrets as well.

apiVersion: application.giantswarm.io/v1alpha1
kind: App
metadata:
  name: hello-world
  namespace: i5h93
spec:
   name: hello-world-app
   namespace: kube-system
   catalog: giantswarm
   config:
      configMap:
         name: hello-world-values
         namespace: i5h93
   extraConfigs:
      - kind: configMap
        name: hello-world-post-user
        namespace: i5h93
        priority: 125
      - kind: configMap
        name: hello-world-pre-user
        namespace: i5h93
        priority: 75
      - kind: configMap
        name: hello-world-pre-cluster
        namespace: i5h93
      - kind: configMap
        name: hello-world-final
        namespace: i5h93
        priority: 125
      - kind: configMap
        name: hello-world-high-priority
        namespace: i5h93
        priority: 10
   userConfig:
      configMap:
         name: hello-world-app-user-values
         namespace: i5h93

The merge order for ConfigMaps (with P as the indicated or calculated priority) will be:

1. Catalog (P = 0)
2. Configmap: hello-world-high-priority (P = 10)
3. Configmap: hello-world-pre-cluster (P = 25)
4. Configmap: hello-world-values (P = 50)
5. Configmap: hello-world-pre-user (P = 75)
6. Configmap: hello-world-app-user-values (P = 100)
7. Configmap: hello-world-post-user (P = 125, position in the list: `1)
8. Configmap: hello-world-final (P = 125, position in the list: 4)

Format of values in ConfigMap and Secret

The ConfigMap and Secret must contain a .data.values key, under which all configuration values are kept, as a string of valid YAML. For secrets, the string must be base64 encoded, as is required by kubernetes.

In this context, the secret is used to populate the values file with secret information, it’s not used to create secrets on the workload cluster.

Example ConfigMap

apiVersion: v1
kind: configmap
metadata:
  name: hello-world-user-values
  namespace: i5h93
data:
  values: |
    colors:
      background: "red"    

Example secret

apiVersion: v1
kind: secret
metadata:
  name: hello-world-user-secrets
  namespace: i5h93
data:
  values: "Y29sb3I6CiAgc2VjcmV0Q29sb3I6ICJibHVlIgo="

Applying configuration values

There are many approaches to apply resources in kubernetes, which go beyond the scope of this article. You can test the examples by running kubectl apply to the platform API. For more advanced use cases, we advocate using GitOps to maintain your configuration in a Git repositories always in sync with your clusters.

Note: Depending on your installation you might not have access to the platform API yet. Please contact your account engineer if you would like more information about that or follow the getting started page to learn how to configure it.