# Kubernetes Addons and Addon Manager

## Addons
With kOps you manage addons by using kubectl.

(For a description of the addon-manager, please see [addon_management](#addon-management).)

Addons in Kubernetes are traditionally done by copying files to `/etc/kubernetes/addons` on the master.  But this
doesn't really make sense in HA master configurations.  We also have kubectl available, and addons are just a thin
wrapper over calling kubectl.

The command `kops create cluster` does not support specifying addons to be added to the cluster when it is created. Instead they can be added after cluster creation using kubectl. Alternatively when creating a cluster from a yaml manifest, addons can be specified using `spec.addons`.
```yaml
spec:
  addons:
  - manifest: kubernetes-dashboard
  - manifest: s3://kops-addons/addon.yaml
```

This document describes how to install some common addons and how to create your own custom ones.

### Custom addons

The docs about the [addon management](#addon-management) describe in more detail how to define a addon resource with regards to versioning.
Here is a minimal example of an addon manifest that would install two different addons.

```yaml
kind: Addons
metadata:
  name: example
spec:
  addons:
  - name: foo.addons.org.io
    version: 0.0.1
    selector:
      k8s-addon: foo.addons.org.io
    manifest: foo.addons.org.io/v0.0.1.yaml
  - name: bar.addons.org.io
    version: 0.0.1
    selector:
      k8s-addon: bar.addons.org.io
    manifest: bar.addons.org.io/v0.0.1.yaml
```

In this example the folder structure should look like this;

```
addon.yaml
  foo.addons.org.io
    v0.0.1.yaml
  bar.addons.org.io
    v0.0.1.yaml
```

The yaml files in the foo/bar folders can be any kubernetes resource. Typically this file structure would be pushed to S3 or another of the supported backends and then referenced as above in `spec.addons`. In order for master nodes to be able to access the S3 bucket containing the addon manifests, one might have to add additional iam policies to the master nodes using `spec.additionalPolicies`, like so;
```yaml
spec:
  additionalPolicies:
    master: |
      [
        {
          "Effect": "Allow",
          "Action": [
            "s3:GetObject"
          ],
          "Resource": ["arn:aws:s3:::kops-addons/*"]
        },
        {
          "Effect": "Allow",
          "Action": [
            "s3:GetBucketLocation",
            "s3:ListBucket"
          ],
          "Resource": ["arn:aws:s3:::kops-addons"]
        }
      ]
```
The masters will poll for changes in the bucket and keep the addons up to date.

### Ambassador

The [Ambassador API Gateway](https://getambassador.io/) provides all the functionality of a traditional ingress
controller (i.e., path-based routing) while exposing many additional capabilities such as authentication, URL rewriting,
CORS, rate limiting, and automatic metrics collection.

Install using:
```
kubectl create -f https://raw.githubusercontent.com/kubernetes/kops/master/addons/ambassador/ambassador-operator.yaml
```

Detailed installation instructions in the [addon documentation](https://github.com/kubernetes/kops/blob/master/addons/ambassador/README.md).
See [Ambassador documentation](https://www.getambassador.io/docs/) on configuration and usage.

### Dashboard

The [dashboard project](https://github.com/kubernetes/dashboard) provides a nice administrative UI:

Install using:
```
kubectl create -f https://raw.githubusercontent.com/kubernetes/kops/master/addons/kubernetes-dashboard/v1.10.1.yaml
```

And then follow the instructions in the [dashboard documentation](https://github.com/kubernetes/dashboard/wiki/Accessing-Dashboard---1.7.X-and-above) to access the dashboard.

The login credentials are:

* Username: `admin`
* Password: get by running `kops get secrets kube --type secret -oplaintext` or `kubectl config view --minify`

#### RBAC

It's necessary to add your own RBAC permission to the dashboard. Please read the [RBAC](https://kubernetes.io/docs/admin/authorization/rbac/) docs before applying permissions.

Below you see an example giving **cluster-admin access** to the dashboard.

```yaml
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: kubernetes-dashboard
  labels:
    k8s-app: kubernetes-dashboard
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
- kind: ServiceAccount
  name: kubernetes-dashboard
  namespace: kube-system
```

### Monitoring with Heapster - Standalone

Monitoring supports the horizontal pod autoscaler.

Install using:
```
kubectl create -f https://raw.githubusercontent.com/kubernetes/kops/master/addons/monitoring-standalone/v1.11.0.yaml
```
Please note that [heapster is retired](https://github.com/kubernetes/heapster/blob/master/docs/deprecation.md). Consider using [metrics-server](https://github.com/kubernetes-incubator/metrics-server) and a third party metrics pipeline to gather Prometheus-format metrics instead.

### Monitoring with Prometheus Operator + kube-prometheus

The [Prometheus Operator](https://github.com/coreos/prometheus-operator/) makes the Prometheus configuration Kubernetes native and manages and operates Prometheus and Alertmanager clusters. It is a piece of the puzzle regarding full end-to-end monitoring.

[kube-prometheus](https://github.com/coreos/prometheus-operator/blob/master/contrib/kube-prometheus) combines the Prometheus Operator with a collection of manifests to help getting started with monitoring Kubernetes itself and applications running on top of it.

```console
kubectl apply -f https://raw.githubusercontent.com/kubernetes/kops/master/addons/prometheus-operator/v0.26.0.yaml
```

### Route53 Mapper

*This addon is deprecated. Please use [external-dns](https://github.com/kubernetes-sigs/external-dns) instead.*

Please note that kOps installs a Route53 DNS controller automatically (it is required for cluster discovery).
The functionality of the route53-mapper overlaps with the dns-controller, but some users will prefer to
use one or the other.
[README for the included dns-controller](https://github.com/kubernetes/kops/blob/master/dns-controller/README.md)

route53-mapper automates creation and updating of entries on Route53 with `A` records pointing
to ELB-backed `LoadBalancer` services created by Kubernetes. Install using:

The project is created by wearemolecule, and maintained at
[wearemolecule/route53-kubernetes](https://github.com/wearemolecule/route53-kubernetes).
[Usage instructions](https://github.com/kubernetes/kops/blob/master/addons/route53-mapper/README.md)

```
kubectl apply -f https://raw.githubusercontent.com/kubernetes/kops/master/addons/route53-mapper/v1.3.0.yml
```

## Addon Management

kOps incorporates management of some addons; we _have_ to manage some addons which are needed before
the kubernetes API is functional.

In addition, kOps offers end-user management of addons via the `channels` tool (which is still experimental,
but we are working on making it a recommended part of kubernetes addon management).  We ship some
curated addons in the [addons directory](https://github.com/kubernetes/kops/tree/master/addons), more information in the [addons document](addons.md).


kOps uses the `channels` tool for system addon management also.  Because kOps uses the same tool
for *system* addon management as it does for *user* addon management, this means that
addons installed by kOps as part of cluster bringup can be managed alongside additional addons.
(Though note that bootstrap addons are much more likely to be replaced during a kOps upgrade).

The general kOps philosophy is to try to make the set of bootstrap addons minimal, and
to make installation of subsequent addons easy.

Thus, `kube-dns` and the networking overlay (if any) are the canonical bootstrap addons.
But addons such as the dashboard or the EFK stack are easily installed after kOps bootstrap,
with a `kubectl apply -f https://...` or with the channels tool.

In future, we may as a convenience make it easy to add optional addons to the kOps manifest,
though this will just be a convenience wrapper around doing it manually.

### Update BootStrap Addons

If you want to update the bootstrap addons, you can run the following command to show you which addons need updating. Add `--yes` to actually apply the updates.

**channels apply channel s3://*KOPS_S3_BUCKET*/*CLUSTER_NAME*/addons/bootstrap-channel.yaml**


### Versioning

The channels tool adds a manifest-of-manifests file, of `Kind: Addons`, which allows for a description
of the various manifest versions that are available.  In this way kOps can manage updates
as new versions of the addon are released.  For example,
the [dashboard addon](https://github.com/kubernetes/kops/blob/master/addons/kubernetes-dashboard/addon.yaml)
lists multiple versions.

For example, a typical addons declaration might looks like this:

```yaml
  - version: 1.4.0
    selector:
      k8s-addon: kubernetes-dashboard.addons.k8s.io
    manifest: v1.4.0.yaml
 - version: 1.5.0
    selector:
      k8s-addon: kubernetes-dashboard.addons.k8s.io
    manifest: v1.5.0.yaml
```

That declares two versions of an addon, with manifests at `v1.4.0.yaml` and at `v1.5.0.yaml`.
These are evaluated as relative paths to the Addons file itself.  (The channels tool supports
a few more protocols than `kubectl` - for example `s3://...` for S3 hosted manifests).

The `version` field gives meaning to the alternative manifests.  This is interpreted as a
semver.  The channels tool keeps track of the current version installed (currently by means
of an annotation on the `kube-system` namespace).

The channel tool updates the installed version when any of the following conditions apply.

* The version declared in the addon manifest is greater then the currently installed version.
* The version number's match, but the ids are different
* The version number and ids match, but the hash of the addon's manifest has changed since it was installed.


This means that a user can edit a deployed addon, and changes will not be replaced, until a new version of the addon is installed. The long-term direction here is that addons will mostly be configured through a ConfigMap or Secret object, and that the addon manager will (TODO) not replace the ConfigMap.

The `selector` determines the objects which make up the addon.  This will be used
to construct a `--prune` argument (TODO), so that objects that existed in the
previous but not the new version will be removed as part of an upgrade.

### Kubernetes Version Selection

The addon manager now supports a `kubernetesVersion` field, which is a semver range specifier
on the kubernetes version.  If the targeted version of kubernetes does not match the semver
specified, the addon version will be ignored.

This allows you to have different versions of the manifest for significant changes to the
kubernetes API.  For example, 1.6 changed the taints & tolerations to a field, and RBAC moved
to beta.  As such it is easier to have two separate manifests.

For example:

```yaml
  - version: 1.5.0
    selector:
      k8s-addon: kube-dashboard.addons.k8s.io
    manifest: v1.5.0.yaml
    kubernetesVersion: "<1.6.0"
    id: "pre-k8s-16"
 - version: 1.6.0
    selector:
      k8s-addon: kube-dashboard.addons.k8s.io
    manifest: v1.6.0.yaml
    kubernetesVersion: ">=1.6.0"
    id: "k8s-16"
```

On kubernetes versions before 1.6, we will install `v1.5.0.yaml`, whereas from kubernetes
versions 1.6 on we will install `v1.6.0.yaml`.

Note that we remove the `pre-release` field of the kubernetes semver, so that `1.6.0-beta.1`
will match `>=1.6.0`.  This matches the way kubernetes does pre-releases.

### Semver is not enough: `id`

However, semver is insufficient here with the kubernetes version selection.  The problem
arises in the following scenario:

* Install k8s 1.5, 1.5 version of manifest is installed
* Upgrade to k8s 1.6, 1.6 version of manifest is installed
* Downgrade to k8s 1.5; we want the 1.5 version of the manifest to be installed but the 1.6 version
  will have a semver that is greater than or equal to the 1.5 semver.

We need a way to break the ties between the semvers, and thus we introduce the `id` field.

Thus a manifest will actually look like this:

```yaml
  - version: 1.6.0
    selector:
      k8s-addon: kube-dns.addons.k8s.io
    manifest: pre-k8s-16.yaml
    kubernetesVersion: "<1.6.0"
    id: "pre-k8s-16"
 - version: 1.6.0
    selector:
      k8s-addon: kube-dns.addons.k8s.io
    manifest: k8s-16.yaml
    kubernetesVersion: ">=1.6.0"
    id: "k8s-16"
```

Note that the two addons have the same version, but a different `kubernetesVersion` selector.
But they have different `id` values; addons with matching semvers but different `id`s will
be upgraded.  (We will never downgrade to an older semver though, regardless of `id`)

So now in the above scenario after the downgrade to 1.5, although the semver is the same,
the id will not match, and the `pre-k8s-16` will be installed.  (And when we upgrade back
to 1.6, the `k8s-16` version will be installed.

A few tips:

* The `version` can now more closely mirror the upstream version.
* The manifest names should probably incorporate the `id`, for maintainability.
