Merge pull request #3592 from xrstf/prod-docs

begin docs page with production tips

Author: kcp-ci-bot

docs/content/setup/.pages

@@ -4,3 +4,4 @@ nav:
     - helm.md
     - kubectl-plugin.md
     - integrations.md
+    - production.md

docs/content/setup/production.md

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+---
+description: >
+  Tips and notes for running a production-grade kcp setup.
+---
+
+# Production Setup
+
+This document collects notes and tips on how to run a production-grade kcp setup.
+
+## Overview
+
+Running kcp consists of mainly two challenges:
+
+* Running reliable **etcd** clusters for each kcp shard.
+* Running **kcp** and dealing with its **sharding** to distribute load and limit the impact of
+  downtimes to a subset of the entire kcp setup.
+
+## Running etcd
+
+Just like Kubernetes, kcp uses [etcd](https://etcd.io/) as its database: each (root)shard uses its own
+etcd cluster.
+
+The etcd documentation already contains a great number of [operations guides](https://etcd.io/docs/v3.7/op-guide/)
+for common operations like performing backups, monitoring the health etc. Administrators should
+familiarize themselves with the practices laid out there.
+
+### Kubernetes
+
+When running etcd inside Kubernetes, an operator can greatly help in running etcd.
+[Etcd Druid](https://gardener.github.io/etcd-druid/) is one of them and offers great support for
+operations tasks and the entire etcd lifecycle. Etcd clusters managed by Etcd Druid can be seamlessly
+used with kcp.
+
+### High Availability
+
+Care should be taken to distribute the etcd pods across availability zones and/or different nodes.
+This ensures that node failure will not immediately bring down an entire etcd cluster. Please refer
+to the [Etcd Druid documentation](https://gardener.github.io/etcd-druid/proposals/01-multi-node-etcd-clusters.html?h=affinity#high-availability)
+for more details and configuration examples.
+
+### TLS
+
+It is highly recommended to enable TLS in etcd to encrypt traffic in-transtit between kcp and etcd.
+When using Kubernetes, [cert-manager](https://cert-manager.io/) is a great choice for managing CAs
+and certificates in your cluster, and it can also provide certificates for use in etcd.
+
+On the kcp side, all that is required is to configure three CLI flags:
+
+* `--etcd-certfile`
+* `--etcd-keyfile`
+* `--etcd-cafile`
+
+When using cert-manager, all three files are available in the Secret that is created for the
+Certificate object.
+
+When using Etcd Druid you have to manually create the necessary certificates or make use of one of
+the community Helm charts like [hajowieland/etcd-druid-certs](https://artifacthub.io/packages/helm/hajowieland/etcd-druid-certs).
+
+### Backups
+
+As with any database, etcd clusters should be backed up regularly. This is especially important with
+etcd because a permanent quorum loss can make the entire database unavailable, even though the data
+is technically in some form still there.
+
+Using an operator like the aforementioned Etcd Druid can greatly help in performing backups and
+restores.
+
+### Encryption
+
+kcp supports encryption-at-rest for its storage backend, allowing administrators to configure
+encryption keys or integration with external key-management systems to encrypt data written to disk.
+
+Please refer to the [Kubernetes documentation](https://kubernetes.io/docs/tasks/administer-cluster/encrypt-data/)
+for more information on configuring and using encryption in kcp.
+
+Since each shard and its etcd is independent from other shards, the encryption configuration can be
+different per shard, if desired.
+
+### Scaling
+
+etcd can be scaled to some degree by adding more resources and/or more members to an etcd cluster,
+however [hard limits](https://etcd.io/docs/v3.7/dev-guide/limit/) set an upper boundary. It is
+important to monitor etcd performance to assign resources accordingly.
+
+Note that using scaling solutions like the Vertical Pod Autoscaler (VPA), care must be taken so that
+not too many etcd members restart simultaneously or a permanent loss of quorum can occur, which would
+require restoring etcd from a backup.
+
+## Running kcp
+
+Kubernetes is the native habitat of kcp and its recommended runtime environment. The kcp project
+offers two ways of running kcp in Kubernetes:
+
+* via [Helm chart](https://github.com/kcp-dev/helm-charts/)
+* using the [kcp-operator](https://docs.kcp.io/kcp-operator/)
+
+While still in its early stages, the kcp-operator is aimed to be the recommended approach to running
+kcp: it offers more features than the Helm charts and can actively reconcile missing/changed
+resources on its own.
+
+### Sharding
+
+kcp supports the concept of sharding to spread the workload horizontally across kcp processes. Even
+if the database behind kcp would offer infinite performance at zero cost, kcp itself cannot scale
+vertically indefinitely: each logical cluster requires a minimum of runtime resources, even if the
+cluster is not actively used.
+
+New workspaces in kcp are spread evenly across all available shards, however as of kcp 0.28, this
+does not take into account the current number of logicalclusters on each shard. This means once
+every existing shard has reached its administrator-defined limit, simply adding a new shard will not
+make kcp schedule all new clusters onto it, but still distribute them evenly. There is currently
+no mechanism to mark shards as "full" or unavailable for schedulding and the kcp scheduled does not
+take shard metrics into account.
+
+It's therefore recommended to start with a sharded setup instead of working with a single root shard
+only. This not only improves realiability and performance, but can also help ensure newly developed
+kcp client software does not by accident make false assumptions about sharding.
+
+### High Availability
+
+To improve resilience against node failures, it is strongly recommended to not just spread the
+workload across multiple shards, but also to ensure that shard pods are distributed across nodes or
+availability zones. The same advice for etcd applies to kcp as well: Use anti-affinities to ensure
+pods are scheduled properly.
+
+### Backups
+
+All kcp data is stored in etcd, there is no need to perform a dedicated kcp backup.