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https://github.com/mittwald/kubernetes-replicator

Kubernetes controller for synchronizing secrets & config maps across namespaces
https://github.com/mittwald/kubernetes-replicator

golang kubernetes kubernetes-configmap kubernetes-controller kubernetes-secrets

Last synced: 3 months ago
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Kubernetes controller for synchronizing secrets & config maps across namespaces

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# ConfigMap, Secret and Role, RoleBinding and ServiceAccount replication for Kubernetes



![Build Status](https://github.com/mittwald/kubernetes-replicator/workflows/Compile%20&%20Test/badge.svg)



This repository contains a custom Kubernetes controller that can be used to make

secrets and config maps available in multiple namespaces.



## Contents



1. [Deployment](#deployment)

    1. [Using Helm](#using-helm)

    1. [Manual](#manual)

1. [Usage](#usage)

    1. ["Role and RoleBinding replication](#role-and-rolebinding-replication)

    1. ["Push-based" replication](#push-based-replication)

    1. ["Pull-based" replication](#pull-based-replication)

        1. [1. Create the source secret](#step-1-create-the-source-secret)

        1. [2. Create empty secret](#step-2-create-an-empty-destination-secret)

        1. [Special case: TLS secrets](#special-case-tls-secrets)



## Deployment



### Using Helm



1. Add the Mittwald Helm Repo:

    ```shellsession

    $ helm repo add mittwald https://helm.mittwald.de

    "mittwald" has been added to your repositories



    $ helm repo update

    Hang tight while we grab the latest from your chart repositories...

    ...Successfully got an update from the "mittwald" chart repository

    Update Complete. ⎈ Happy Helming!⎈

    ```



2. Upgrade or install `kubernetes-replicator`

    `helm upgrade --install kubernetes-replicator mittwald/kubernetes-replicator`



### Manual



```shellsession

$ # Create roles and service accounts

$ kubectl apply -f https://raw.githubusercontent.com/mittwald/kubernetes-replicator/master/deploy/rbac.yaml

$ # Create actual deployment

$ kubectl apply -f https://raw.githubusercontent.com/mittwald/kubernetes-replicator/master/deploy/deployment.yaml

```



## Usage



### Role and RoleBinding replication



To create a new role, your own account needs to have at least the same set of privileges as the role you're trying to create. The chart currently offers two options to grant these permissions to the service account used by the replicator:



- Set the value `grantClusterAdmin`to `true`, which grants the service account admin privileges. This is set to `false` by default, as having a service account with that level of access might be undesirable due to the potential security risks attached.



- Set the lists of needed api groups and resources explicitly. These can be specified using the value `privileges`. `privileges` is a list that contains pairs of api group and resource lists.



  Example:



  ```yaml

  serviceAccount:

    create: true

    annotations: {}

    name:

    privileges:

      - apiGroups: [ "", "apps", "extensions" ]

        resources: ["secrets", "configmaps", "roles", "rolebindings",

        "cronjobs", "deployments", "events", "ingresses", "jobs", "pods", "pods/attach", "pods/exec", "pods/log", "pods/portforward", "services"]

      - apiGroups: [ "batch" ]

        resources:  ["configmaps", "cronjobs", "deployments", "events", "ingresses", "jobs", "pods", "pods/attach", "pods/exec", "pods/log", "pods/portforward", "services"]

  ```



  These settings permit the replication of Roles and RoleBindings with privileges for the api groups `""`. `apps`, `batch` and `extensions` on the resources specified.



### "Push-based" replication



Push-based replication will "push out" the secrets, configmaps, roles and rolebindings into namespaces when new namespaces are created or when the secret/configmap/roles/rolebindings changes.



There are two general methods for push-based replication:



- name-based; this allows you to either specify your target namespaces _by name_ or by regular expression (which should match the namespace name). To use name-based push replication, add a `replicator.v1.mittwald.de/replicate-to` annotation to your secret, role(binding) or configmap. The value of this annotation should contain a comma separated list of permitted namespaces or regular expressions. (Example: `namespace-1,my-ns-2,app-ns-[0-9]*` will replicate only into the namespaces `namespace-1` and `my-ns-2` as well as any namespace that matches the regular expression `app-ns-[0-9]*`).



  Example:



  ```yaml

  apiVersion: v1

  kind: Secret

  metadata:

    annotations:

      replicator.v1.mittwald.de/replicate-to: "my-ns-1,namespace-[0-9]*"

  data:

    key1: 

  ```



- label-based; this allows you to specify a label selector that a namespace should match in order for a secret, role(binding) or configmap to be replicated. To use label-based push replication, add a `replicator.v1.mittwald.de/replicate-to-matching` annotation to the object you want to replicate. The value of this annotation should contain an arbitrary [label selector](https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/#label-selectors).



  Example:



  ```yaml

  apiVersion: v1

  kind: Secret

  metadata:

    annotations:

      replicator.v1.mittwald.de/replicate-to-matching: >

        my-label=value,my-other-label,my-other-label notin (foo,bar)

  data:

    key1: 

  ```



When the labels of a namespace are changed, any resources that were replicated by labels into the namespace and no longer qualify for replication under the new set of labels will be deleted. Afterwards any resources that now match the updated labels will be replicated into the namespace.



It is possible to use both methods of push-based replication together in a single resource, by specifying both annotations.



### "Pull-based" replication



Pull-based replication makes it possible to create a secret/configmap/role/rolebindings and select a "source" resource

from which the data is replicated from.



#### Step 1: Create the source secret



If a secret or configMap needs to be replicated to other namespaces, annotations should be added in that object

permitting replication.



  - Add `replicator.v1.mittwald.de/replication-allowed` annotation with value `true` indicating that the object can be

    replicated.

  - Add `replicator.v1.mittwald.de/replication-allowed-namespaces` annotation. Value of this annotation should contain

    a comma separated list of permitted namespaces or regular expressions. For example `namespace-1,my-ns-2,app-ns-[0-9]*`:

    in this case replication will be performed only into the namespaces `namespace-1` and `my-ns-2` as well as any

    namespace that matches the regular expression `app-ns-[0-9]*`.



    ```yaml

    apiVersion: v1

    kind: Secret

    metadata:

      annotations:

        replicator.v1.mittwald.de/replication-allowed: "true"

        replicator.v1.mittwald.de/replication-allowed-namespaces: "my-ns-1,namespace-[0-9]*"

    data:

      key1: 

    ```



#### Step 2: Create an empty destination secret



Add the annotation `replicator.v1.mittwald.de/replicate-from` to any Kubernetes secret or config map object. The value

of that annotation should contain the the name of another secret or config map (using `/` notation).



```yaml

apiVersion: v1

kind: Secret

metadata:

  name: secret-replica

  annotations:

    replicator.v1.mittwald.de/replicate-from: default/some-secret

data: {}

```



The replicator will then copy the `data` attribute of the referenced object into the annotated object and keep them in

sync.



#### Special case: TLS secrets



Secrets of type `kubernetes.io/tls` are treated in a special way and need to have a `data["tls.crt"]` and a

`data["tls.key"]` property to begin with. In the replicated secrets, these properties need to be present to begin with,

but they may be empty:



```yaml

apiVersion: v1

kind: Secret

metadata:

  name: tls-secret-replica

  annotations:

    replicator.v1.mittwald.de/replicate-from: default/some-tls-secret

type: kubernetes.io/tls

data:

  tls.key: ""

  tls.crt: ""

```



#### Special case: Docker registry credentials



Secrets of type `kubernetes.io/dockerconfigjson` also require special treatment. These secrets require to have a

`.dockerconfigjson` key that needs to require valid JSON. For this reason, a replicated secret of this type should be

created as follows:



```yaml

apiVersion: v1

kind: Secret

metadata:

  name: docker-secret-replica

  annotations:

    replicator.v1.mittwald.de/replicate-from: default/some-docker-secret

type: kubernetes.io/dockerconfigjson

data:

  .dockerconfigjson: e30K

```



#### Special case: Strip labels while replicate the resources.



Operators like [https://github.com/strimzi/strimzi-kafka-operator](strimzi-kafka-operator) implement an own garbage collection based on specific labels defined on resources. If mittwald replicator replicate secrets to different namespace, the strimzi-kafka-operator will remove the replicated secrets because from operators point of view the secret is a left-over. To mitigate the issue, set the annotation `replicator.v1.mittwald.de/strip-labels=true` to remove all labels on the replicated resource.



```yaml

apiVersion: v1

kind: Secret

metadata:

  labels:

    app.kubernetes.io/managed-by: "strimzi-kafka-operator"

  name: cluster-ca-certs

  annotations:

    replicator.v1.mittwald.de/strip-labels: "true"

type: kubernetes.io/tls

data:

  tls.key: ""

  tls.crt: ""

```



#### Special case: Resource with .metadata.ownerReferences



Sometimes, secrets are generated by external components. Such secrets are configured with an ownerReference. By default, the kubernetes-replicator will delete the

ownerReference in the target namespace.



ownerReference won't work [across different namespaces](https://kubernetes.io/docs/concepts/workloads/controllers/garbage-collection/#owners-and-dependents) and the secret at the destination will be removed by the kubernetes garbage collection.



To keep `ownerReferences` at the destination, set the annotation `replicator.v1.mittwald.de/keep-owner-references=true`



```yaml

apiVersion: v1

kind: Secret

metadata:

  name: docker-secret-replica

  annotations:

    replicator.v1.mittwald.de/keep-owner-references: "true"

  ownerReferences:

    - apiVersion: v1

      kind: Deployment

      name: owner

      uid: "1234"

type: kubernetes.io/tls

data:

  tls.key: ""

  tls.crt: ""

```



See also: https://github.com/mittwald/kubernetes-replicator/issues/120