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Cluster Decision Resource Generator¶
The cluster decision resource generates a list of Argo CD clusters. This is done using duck-typing, which does not require knowledge of the full shape of the referenced kubernetes resource. The following is an example of a cluster-decision-resource-based ApplicationSet generator:
yaml
apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
name: guestbook
namespace: argocd
spec:
generators:
- clusterDecisionResource:
# ConfigMap with GVK information for the duck type resource
configMapRef: my-configmap
name: quak # Choose either "name" of the resource or "labelSelector"
labelSelector:
matchLabels: # OPTIONAL
duck: spotted
matchExpressions: # OPTIONAL
- key: duck
operator: In
values:
- "spotted"
- "canvasback"
# OPTIONAL: Checks for changes every 60sec (default 3min)
requeueAfterSeconds: 60
template:
metadata:
name: '{{name}}-guestbook'
spec:
project: "default"
source:
repoURL: https://github.com/argoproj/argocd-example-apps/
targetRevision: HEAD
path: guestbook
destination:
server: '{{clusterName}}' # 'server' field of the secret
namespace: guestbook
The quak
resource, referenced by the ApplicationSet clusterDecisionResource
generator:
yaml
apiVersion: mallard.io/v1beta1
kind: Duck
metadata:
name: quak
spec: {}
status:
# Duck-typing ignores all other aspects of the resource except
# the "decisions" list
decisions:
- clusterName: cluster-01
- clusterName: cluster-02
The ApplicationSet
resource references a ConfigMap
that defines the resource to be used in this duck-typing. Only one ConfigMap is required per ArgoCD
instance, to identify a resource. You can support multiple resource types by creating a ConfigMap
for each.
yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: my-configmap
data:
# apiVersion of the target resource
apiVersion: mallard.io/v1beta1
# kind of the target resource
kind: ducks
# status key name that holds the list of Argo CD clusters
statusListKey: decisions
# The key in the status list whose value is the cluster name found in Argo CD
matchKey: clusterName
(The full example can be found here.)
This example leverages the cluster management capabilities of the open-cluster-management.io community. By creating a ConfigMap
with the GVK for the open-cluster-management.io
Placement rule, your ApplicationSet can provision to different clusters in a number of novel ways. One example is to have the ApplicationSet maintain only two Argo CD Applications across 3 or more clusters. Then as maintenance or outages occur, the ApplicationSet will always maintain two Applications, moving the application to available clusters under the Placement rule's direction.
How it works¶
The ApplicationSet needs to be created in the Argo CD namespace, placing the ConfigMap
in the same namespace allows the ClusterDecisionResource generator to read it. The ConfigMap
stores the GVK information as well as the status key definitions. In the open-cluster-management example, the ApplicationSet generator will read the kind placementrules
with an apiVersion of apps.open-cluster-management.io/v1
. It will attempt to extract the list of clusters from the key decisions
. It then validates the actual cluster name as defined in Argo CD against the value from the key clusterName
in each of the elements in the list.
The ClusterDecisionResource generator passes the 'name', 'server' and any other key/value in the duck-type resource's status list as parameters into the ApplicationSet template. In this example, the decision array contained an additional key clusterName
, which is now available to the ApplicationSet template.
Clusters listed as Status.Decisions
must be predefined in Argo CD
The cluster names listed in the Status.Decisions
must be defined within Argo CD, in order to generate applications for these values. The ApplicationSet controller does not create clusters within Argo CD.
The Default Cluster list key is clusters
.