1# Legacy Cluster add-ons
2
3For more information on add-ons see [the documentation](https://kubernetes.io/docs/concepts/cluster-administration/addons/).
4
5## Overview
6
7Cluster add-ons are resources like Services and Deployments (with pods) that are
8shipped with the Kubernetes binaries and are considered an inherent part of the
9Kubernetes clusters.
10
11There are currently two classes of add-ons:
12- Add-ons that will be reconciled.
13- Add-ons that will be created if they don't exist.
14
15More details could be found in [addon-manager/README.md](addon-manager/README.md).
16
17## Cooperating Horizontal / Vertical Auto-Scaling with "reconcile class addons"
18
19"Reconcile" class addons will be periodically reconciled to the original state given
20by the initial config. In order to make Horizontal / Vertical Auto-scaling functional,
21the related fields in config should be left unset. More specifically, leave `replicas`
22in `ReplicationController` / `Deployment` / `ReplicaSet` unset for Horizontal Scaling,
23leave `resources` for container unset for Vertical Scaling. The periodic reconcile
24won't clobbered these fields, hence they could be managed by Horizontal / Vertical
25Auto-scaler.
26
27## Add-on naming
28
29The suggested naming for most of the resources is `<basename>` (with no version number).
30Though resources like `Pod`, `ReplicationController` and `DaemonSet` are exceptional.
31It would be hard to update `Pod` because many fields in `Pod` are immutable. For
32`ReplicationController` and `DaemonSet`, in-place update may not trigger the underlying
33pods to be re-created. You probably need to change their names during update to trigger
34a complete deletion and creation.
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