Mapping to Downstream Clusters

Fleet in Rancher allows users to manage clusters easily as if they were one cluster. Users can deploy bundles, which can be comprised of deployment manifests or any other Kubernetes resource, across clusters using grouping configuration.

Mapping to Downstream Clusters - 图1info

Multi-cluster Only: This approach only applies if you are running Fleet in a multi-cluster style If no targets are specified, i.e. when using a single-cluster, the bundles target the default cluster group.

When deploying GitRepos to downstream clusters the clusters must be mapped to a target.

Defining Targets

The deployment targets of GitRepo is done using the spec.targets field to match clusters or cluster groups. The YAML specification is as below.

  1. kind: GitRepo
  2. apiVersion: fleet.cattle.io/v1alpha1
  3. metadata:
  4.   name: myrepo
  5.   namespace: clusters
  6. spec:
  7.   repo: https://github.com/rancher/fleet-examples
  8.   paths:
  9.   - simple
  11.   # Targets are evaluated in order and the first one to match is used. If
  12.   # no targets match then the evaluated cluster will not be deployed to.
  13.   targets:
  14.   # The name of target. This value is largely for display and logging.
  15.   # If not specified a default name of the format "target000" will be used
  16.   - name: prod
  17.     # A selector used to match clusters.  The structure is the standard
  18.     # metav1.LabelSelector format. If clusterGroupSelector or clusterGroup is specified,
  19.     # clusterSelector will be used only to further refine the selection after
  20.     # clusterGroupSelector and clusterGroup is evaluated.
  21.     clusterSelector:
  22.       matchLabels:
  23.         env: prod
  24.     # A selector used to match cluster groups.
  25.     clusterGroupSelector:
  26.       matchLabels:
  27.         region: us-east
  28.     # A specific clusterGroup by name that will be selected
  29.     clusterGroup: group1
  30.     # A specific cluster by name that will be selected
  31.     clusterName: cluster1

Target Matching

All clusters and cluster groups in the same namespace as the GitRepo will be evaluated against all targets. If any of the targets match the cluster then the GitRepo will be deployed to the downstream cluster. If no match is made, then the GitRepo will not be deployed to that cluster.

There are three approaches to matching clusters. One can use cluster selectors, cluster group selectors, or an explicit cluster group name. All criteria is additive so the final match is evaluated as “clusterSelector && clusterGroupSelector && clusterGroup”. If any of the three have the default value it is dropped from the criteria. The default value is either null or “”. It is important to realize that the value {} for a selector means “match everything.”

  1. targets:
  2.   # Match everything
  3.   - clusterSelector: {}
  4.   # Selector ignored
  5.   - clusterSelector: null

You can also match clusters by name:

  1. targets:
  2.   - clusterName: fleetname

When using Fleet in Rancher, make sure to put the name of the clusters.fleet.cattle.io resource.

Default Target

If no target is set for the GitRepo then the default targets value is applied. The default targets value is as below.

  1. targets:
  2. - name: default
  3.   clusterGroup: default

This means if you wish to setup a default location non-configured GitRepos will go to, then just create a cluster group called default and add clusters to it.

Customization per Cluster

Mapping to Downstream Clusters - 图2info

The targets: in the GitRepo resource select clusters to deploy on. The targetCustomizations: in fleet.yaml override Helm values only and do not change targeting.

To demonstrate how to deploy Kubernetes manifests across different clusters with customization using Fleet, we will use multi-cluster/helm/fleet.yaml.

Situation: User has three clusters with three different labels: env=dev, env=test, and env=prod. User wants to deploy a frontend application with a backend database across these clusters.

Expected behavior:

  • After deploying to the dev cluster, database replication is not enabled.
  • After deploying to the test cluster, database replication is enabled.
  • After deploying to the prod cluster, database replication is enabled and Load balancer services are exposed.

Advantage of Fleet:

Instead of deploying the app on each cluster, Fleet allows you to deploy across all clusters following these steps:

  1. Deploy gitRepo https://github.com/rancher/fleet-examples.git and specify the path multi-cluster/helm.
  2. Under multi-cluster/helm, a Helm chart will deploy the frontend app service and backend database service.
  3. The following rule will be defined in fleet.yaml:
  1. targetCustomizations:
  2. - name: dev
  3.   helm:
  4.     values:
  5.       replication: false
  6.   clusterSelector:
  7.     matchLabels:
  8.       env: dev
  10. - name: test
  11.   helm:
  12.     values:
  13.       replicas: 3
  14.   clusterSelector:
  15.     matchLabels:
  16.       env: test
  18. - name: prod
  19.   helm:
  20.     values:
  21.       serviceType: LoadBalancer
  22.       replicas: 3
  23.   clusterSelector:
  24.     matchLabels:
  25.       env: prod

Result:

Fleet will deploy the Helm chart with your customized values.yaml to the different clusters.

Note: Configuration management is not limited to deployments but can be expanded to general configuration management. Fleet is able to apply configuration management through customization among any set of clusters automatically.

Supported Customizations

Additional Examples

Examples using raw Kubernetes YAML, Helm charts, Kustomize, and combinations of the three are in the Fleet Examples repo.