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Synchronize Configuration across Clusters

You can synchronize a ConfigMap or a Secret into different clusters using Kubed. For this you need to provide a kube-config file consisting cluster contexts and specify context names in comma separated format using annotation. Kubed will create a copy of that ConfigMap/Secret in all clusters specified by the annotation. For each cluster, it will sync into source namespace by default, but if namespace specified in the context (in the kube-config file), it will sync into that namespace. Note that, Kubed will not create any namespace, it has to be created beforehand.

If the data in the source ConfigMap/Secret is updated, all the copies will be updated. Either delete the source ConfigMap/Secret or remove the annotation from the source ConfigMap/Secret to remove the copies.

If the list of contexts specified by the annotation is updated, Kubed will synchronize the ConfigMap/Secret accordingly, ie. it will create ConfigMap/Secret in the clusters listed in new annotation (if not already exists) and delete ConfigMap/Secret from the clusters that were synced before but not listed in new annotation.

Note that, Kubed will error out if multiple contexts listed in annotation point same cluster. Also Kubed assumes that none of cluster contexts in kube-config file points the source cluster.

Before You Begin

At first, you need to have a Kubernetes cluster and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube. You also need a kube-config file consisting cluster contexts where you want to sync your ConfigMap/Secret.

Deploy Kubed

To enable config syncer for different clusters, you need a cluster config like below.

$ cat ./docs/examples/cluster-syncer/config.yaml

clusterName: minikube
enableConfigSyncer: true
kubeConfigFile: /srv/kubed/kubeConfigFile
clusterNameOptional. Specifies the source cluster name used in label
enableConfigSyncerRequired. If set to true, ConfigMap/Secret synchronization operation will be enabled.
kubeConfigFileRequired. Specifies the path of kube-config file.

Lets’ consider following demo kube-config file:

$ cat ./docs/examples/config-syncer/demo-kubeconfig.yaml

apiVersion: v1
kind: Config
- name: cluster-1
    certificate-authority-data: ...
- name: cluster-2
    certificate-authority-data: ...
- name: user-1
    client-certificate: ...
    client-key: ...
- name: user-2
    client-certificate: ...
    client-key: ...
- name: context-1
    cluster: cluster-1
    user: user-1
- name: context-2
    cluster: cluster-2
    user: user-2
    namespace: demo-cluster-2

Now, create a Secret with the Kubed cluster config under config.yaml key. Also include required kube-config file under kubeConfigFile key. You can use separate secret for kube-config.

$ kubectl create secret generic kubed-config -n kube-system \
    --from-file=./docs/examples/cluster-syncer/config.yaml \
secret "kubed-config" created

# apply app=kubed label to easily cleanup later
$ kubectl label secret kubed-config app=kubed -n kube-system
secret "kubed-config" labeled

$ kubectl get secret kubed-config -n kube-system -o yaml
apiVersion: v1
  config.yaml: ZW5hYmxlQ29uZmlnU3luY2VyOiB0cnVlCg==
  kubeConfigFile: base64 endoded contents of kube-config file
kind: Secret
  creationTimestamp: 2017-07-26T10:25:33Z
    app: kubed
  name: kubed-config
  namespace: kube-system
  resourceVersion: "25114"
  selfLink: /api/v1/namespaces/kube-system/secrets/kubed-config
  uid: c207c236-71ec-11e7-a5ec-0800273df5f2
type: Opaque

Now, deploy Kubed operator in your cluster following the steps here. It will mount the secret inside operator pod in path /srv/kubed. So kubed cluster config file will be available in path /srv/kubed/config.yaml and kube-config file will be available in path /srv/kubed/kubeConfigFile. Once the operator pod is running, go to the next section.

Synchronize ConfigMap

At first, create a ConfigMap called omni in the demo namespace. This will be our source ConfigMap.

$ kubectl create namespace demo
namespace "demo" created

$ kubectl apply -f ./docs/examples/config-syncer/demo.yaml
configmap "omni" created

Now, apply the "context-1,context-2" annotation to ConfigMap omni.

$ kubectl annotate configmap omni"context-1,context-2" -n demo
configmap "omni" annotated

It will create configmap “omni” in cluster-1 and cluster-2. For cluster-1 it will sync into source namespace demo since no namespace specified in context-1 and for cluster-2 it will sync into demo-cluster-2 namespace since namespace specified in context-2. Here we assume that those namespaces already exits in the respective clusters.

Other concepts like updating source configmap, removing annotation, origin annotation, origin labels, etc. are similar to the tutorial described here.

Next Steps

  • Need to keep some configuration synchronized across namespaces? Try Kubed config syncer.
  • Learn how to use Kubed to protect your Kubernetes cluster from disasters here.
  • Want to keep an eye on your cluster with automated notifications? Setup Kubed event forwarder.
  • Out of disk space because of too much logs in Elasticsearch or metrics in InfluxDB? Configure janitors to delete old data.
  • Wondering what features are coming next? Please visit here.
  • Want to hack on Kubed? Check our contribution guidelines.