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Synchronize Configuration across Namespaces
Say, you are using some Docker private registry. You want to keep its image pull secret synchronized across all namespaces of a Kubernetes cluster. Kubed can do that for you. If a ConfigMap or a Secret has the annotation kubed.appscode.com/sync: "", Kubed will create a copy of that ConfigMap/Secret in all existing namespaces. Kubed will also create this ConfigMap/Secret, when you create a new namespace.
If you want to synchronize ConfigMap/Secret to some selected namespaces instead of all namespaces, you can do that by specifying namespace label-selector in the annotation. For example: kubed.appscode.com/sync: "app=kubed". Kubed will create a copy of that ConfigMap/Secret in all namespaces that matches the label-selector. Kubed will also create this Configmap/Secret in newly created namespace if it matches the label-selector.
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 namespace with the source ConfigMap/Secret is deleted, the copies will also be deleted.
If the value of label-selector specified by annotation is updated, Kubed will synchronize the ConfigMap/Secret accordingly, ie. it will create ConfigMap/Secret in the namespaces that are selected by new label-selector (if not already exists) and delete from namespaces that were synced before but not selected by new label-selector.
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 kind.
Synchronize ConfigMap
In this tutorial, a ConfigMap will be synced across all Kubernetes namespaces using Kubed. You can do the same for Secrets.
To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial. Run the following command to prepare your cluster for this tutorial:
$ kubectl create namespace demo
namespace "demo" created
$ kubectl get namespaces
NAME STATUS AGE
default Active 6h
kube-public Active 6h
kube-system Active 6h
demo Active 4m
Now, create a ConfigMap called omni in the demo namespace. This will be our source ConfigMap.
$ kubectl apply -f ./docs/examples/config-syncer/demo-0.yaml
configmap "omni" created
$ kubectl get configmaps --all-namespaces | grep omni
demo omni 2 7m
$ kubectl get configmaps omni -n demo -o yaml
apiVersion: v1
data:
you: only
leave: once
kind: ConfigMap
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: |
{"apiVersion":"v1","data":{"leave":"once","you":"only"},"kind":"ConfigMap","metadata":{"annotations":{},"name":"omni","namespace":"demo"}}
creationTimestamp: 2017-07-26T13:20:15Z
name: omni
namespace: demo
resourceVersion: "10598"
selfLink: /api/v1/namespaces/demo/configmaps/omni
uid: 2988e9d5-7205-11e7-af79-08002738e55e
Now, apply the kubed.appscode.com/sync: "" annotation to ConfigMap omni. Kubed operator will notice that and copy the ConfigMap in all existing namespaces.
$ kubectl annotate configmap omni kubed.appscode.com/sync="" -n demo
configmap "omni" annotated
$ kubectl get configmaps --all-namespaces | grep omni
default omni 2 1m
demo omni 2 8m
kube-public omni 2 1m
kube-system omni 2 1m
$ kubectl get configmaps omni -n demo -o yaml
apiVersion: v1
data:
you: only
leave: once
kind: ConfigMap
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: |
{"apiVersion":"v1","data":{"leave":"once","you":"only"},"kind":"ConfigMap","metadata":{"annotations":{},"name":"omni","namespace":"demo"}}
kubed.appscode.com/sync: "true"
creationTimestamp: 2017-07-26T13:20:15Z
name: omni
namespace: demo
resourceVersion: "11053"
selfLink: /api/v1/namespaces/demo/configmaps/omni
uid: 2988e9d5-7205-11e7-af79-08002738e55e
Now, create a new namespace called other. Kubed will copy ConfigMap omni into that namespace.
$ kubectl create ns other
namespace "other" created
$ kubectl get configmaps --all-namespaces | grep omni
default omni 2 5m
demo omni 2 12m
kube-public omni 2 5m
kube-system omni 2 5m
other omni 2 1m
Alas! there is a typo is the ConfigMap data. Let’s fix that.
$ kubectl apply -f ./docs/examples/config-syncer/demo-1.yaml
configmap "omni" configured
$ kubectl get configmaps --all-namespaces | grep omni
default omni 2 9m
demo omni 2 16m
kube-public omni 2 9m
kube-system omni 2 9m
other omni 2 5m
$ kubectl get configmaps omni -n other -o yaml
apiVersion: v1
data:
you: only
live: once
kind: ConfigMap
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: |
{"apiVersion":"v1","data":{"live":"once","you":"only"},"kind":"ConfigMap","metadata":{"annotations":{},"name":"omni","namespace":"demo"}}
creationTimestamp: 2017-07-26T13:31:13Z
name: omni
namespace: other
resourceVersion: "11594"
selfLink: /api/v1/namespaces/other/configmaps/omni
uid: b193f40f-7206-11e7-af79-08002738e55e
Kubed operator notices that the source ConfigMap omni has been updated and propagates the change to all the copies in other namespaces.
Namespace Selector
Lets’ change annotation value of source ConfigMap omni.
$ kubectl annotate configmap omni kubed.appscode.com/sync="app=kubed" -n demo --overwrite
configmap "omni" annotated
$ kubectl get configmaps --all-namespaces | grep omni
demo omni 2 8m
Kubed operator removes the ConfigMap from all namespaces (except source) since no namespace matches the label-selector app=kubed.
Now, lets’ apply app=kubed annotation to other namespace. Kubed operator will then sync the ConfigMap to other namespace.
$ kubectl label namespace other app=kubed
namespace "other" labeled
$ kubectl get configmaps --all-namespaces | grep omni
demo omni 2 8m
other omni 2 5m
Restricting Source Namespace
By default, Kubed will watch all namespaces for configmaps and secrets with kubed.appscode.com/sync annotation. But you can restrict the source namespace for configmaps and secrets by passing config.configSourceNamespace value during installation.
$ helm install kubed appscode/kubed \
--namespace=kube-system \
--set imagePullPolicy=Always \
--set config.configSourceNamespace=demo
Remove Annotation
Now, lets’ remove the annotation from source ConfigMap omni. Please note that - after annotation key kubed.appscode.com/sync-. This tells kubectl to remove this annotation from ConfigMap omni.
$ kubectl annotate configmap omni kubed.appscode.com/sync- -n demo
configmap "omni" annotated
$ kubectl get configmaps --all-namespaces | grep omni
demo omni 2 18m
Origin Annotation
Since 0.9.0, Kubed operator will apply kubed.appscode.com/origin annotation on ConfigMap or Secret copies.
Origin Labels
Kubed operator will apply following labels on ConfigMap or Secret copies:
kubed.appscode.com/origin.namekubed.appscode.com/origin.namespacekubed.appscode.com/origin.cluster
This annotations are used by Kubed operator to list the copies for a specific source ConfigMap/Secret.
Cleaning up
To cleanup the Kubernetes resources created by this tutorial, run the following commands:
$ kubectl delete ns other
namespace "other" deleted
$ kubectl delete ns demo
namespace "demo" deleted
To uninstall Kubed operator, please follow the steps here.
Next Steps
- Learn how to sync config-maps or secrets across multiple cluster here.
- Want to hack on Kubed? Check our contribution guidelines.