Merge pull request #4710 from EnterpriseDB/docs/pg4k-pgd/v1-import

product_docs/docs/postgres_distributed_for_kubernetes/1/architecture.mdx

@@ -3,31 +3,196 @@ title: 'Architecture'
 originalFilePath: 'src/architecture.md'
 ---
 
-This section covers the main architectural aspects you need to consider
-when deploying EDB Postgres Distributed for Kubernetes (PG4K-PGD).
+Consider these main architectural aspects 
+when deploying EDB Postgres Distributed in Kubernetes.
 
-PG4K-PGD can be installed within a [single Kubernetes cluster](#single-kubernetes-cluster)
-or across [multiple Kubernetes clusters](#multiple-kubernetes-clusters) - normally
-in different regions.
+EDB Postgres Distributed for Kubernetes is a
+[Kubernetes operator](https://kubernetes.io/docs/concepts/extend-kubernetes/operator/)
+designed to deploy and manage EDB Postgres Distributed clusters
+running in private, public, hybrid, or multi-cloud environments.
+
+## Relationship with EDB Postgres Distributed
+
+[EDB Postgres Distributed (PGD)](https://www.enterprisedb.com/docs/pgd/latest/)
+is a multi-master implementation of Postgres designed for high performance and 
+availability.
+PGD generally requires deployment using
+[Trusted Postgres Architect (TPA)](/pgd/latest/tpa/),
+a tool that uses [Ansible](https://www.ansible.com) to provision and
+deploy PGD clusters.
+
+EDB Postgres Distributed for Kubernetes offers a different way of deploying PGD clusters, leveraging containers
+and Kubernetes. The advantages are that the resulting architecture:
+
+- Is self-healing and robust.
+- Is managed through declarative configuration.
+- Takes advantage of the vast and growing Kubernetes ecosystem.
 
 ## Relationship with EDB Postgres for Kubernetes
 
-A PGD cluster is made up by one or more PGD groups, each having one or more PGD
-nodes. A PGD node in Kubernetes can be assimilated to a Postgres cluster
-without any physical replicas.
-PG4K-PGD internally manages each PGD node using the `Cluster` resource as
-defined by EDB Postgres for Kubernetes (PG4K), specifically a `Cluster` with
-`.spec.instances = 1`.
+A PGD cluster consists of one or more *PGD groups*, each having one or more *PGD
+nodes*. A PGD node is a Postgres database. EDB Postgres Distributed for Kubernetes internally
+manages each PGD node using the `Cluster` resource as defined by EDB Postgres
+for Kubernetes, specifically a cluster with a single instance (that is, no
+replicas).
+
+You can configure the single PostgreSQL instance created by each `Cluster` in the
+[`.spec.cnp` section](pg4k-pgd.v1beta1.md#pgd-k8s-enterprisedb-io-v1beta1-CnpConfiguration)
+of the PGD Group spec.
+
+In EDB Postgres Distributed for Kubernetes, as in EDB Postgres for Kubernetes, the underlying database implementation is responsible
+for data replication. However, it's important to note that failover and
+switchover work differently, entailing Raft election and nominating new
+write leaders. EDB Postgres for Kubernetes handles only the deployment and healing of data nodes.
+
+## Managing PGD using EDB Postgres Distributed for Kubernetes
+
+The EDB Postgres Distributed for Kubernetes operator can manage the complete lifecycle of PGD clusters. As
+such, in addition to PGD nodes (represented as single-instance `Clusters`), it
+needs to manage other objects associated with PGD.
+
+PGD relies on the Raft algorithm for distributed consensus to manage node
+metadata, specifically agreement on a *write leader*. Consensus among data
+nodes is also required for operations such as generating new global sequences
+or performing distributed DDL.
+
+These considerations force additional actors in PGD above database nodes.
+
+EDB Postgres Distributed for Kubernetes manages the following:
+
+-   Data nodes. A node is a database and is managed
+    by EDB Postgres for Kubernetes, creating a `Cluster` with a single instance.
+-   [Witness nodes](https://www.enterprisedb.com/docs/pgd/latest/nodes/#witness-nodes)
+    are basic database instances that don't participate in data
+    replication. Their function is to guarantee that consensus is possible in
+    groups with an even number of data nodes or after network partitions. Witness
+    nodes are also managed using a single-instance `Cluster` resource.
+-   [PGD proxies](https://www.enterprisedb.com/docs/pgd/latest/routing/proxy/)
+    act as Postgres proxies with knowledge of the write leader. PGD proxies need
+    information from Raft to route writes to the current write leader.
+
+### Proxies and routing
+
+PGD groups assume full mesh connectivity of PGD nodes. Each node must be able to
+connect to every other node using the appropriate connection string (a
+`libpq`-style DSN). Write operations don't need to be sent to every node. PGD 
+takes care of replicating data after it's committed to one node.
+
+For performance, we often recommend sending write operations mostly to a
+single node, the  *write leader*. Raft is used to identify which node is the
+write leader and to hold metadata about the PGD nodes. PGD proxies are used to
+transparently route writes to write leaders and to quickly pivot to the new
+write leader in case of switchover or failover.
+
+It's possible to configure *Raft subgroups*, each of which can maintain a
+separate write leader. In EDB Postgres Distributed for Kubernetes, a PGD group containing a PGD proxy
+comprises a Raft subgroup.
+
+Two kinds of routing are available with PGD proxies:
+
+-   Global routing uses the top-level Raft group and maintains one global write
+    leader.
+-   Local routing uses subgroups to maintain separate write leaders. Local
+    routing is often used to achieve geographical separation of writes.
+
+In EDB Postgres Distributed for Kubernetes, local routing is used by default, and a configuration option is
+available to select global routing.
+
+For more information, see the
+[PGD documentation of routing with Raft](https://www.enterprisedb.com/docs/pgd/latest/routing/raft/).
+
+### PGD architectures and high availability
+
+EDB proposes several recommended architectures to make good use of PGD's
+distributed multi-master capabilities and to offer high availability. 
+
+The Always On architectures are built from either one group in a single location
+or two groups in two separate locations.
+See [Choosing your architecture](/pgd/latest/architectures/) in the PGD documentation
+for more information.
+
+## Deploying PGD on Kubernetes
+
+EDB Postgres Distributed for Kubernetes leverages Kubernetes to deploy and manage PGD clusters. As such, some
+adaptations are necessary to translate PGD into the Kubernetes ecosystem.
+
+### Images and operands
+
+You can configure PGD to run one of three Postgres distributions. See the
+[PGD documentation](/pgd/latest/choosing_server/)
+to understand the features of each distribution.
+
+To function in Kubernetes, containers are provided for each Postgres
+distribution. These are the *operands*.
+In addition, the operator images are kept in those same repositories.
+
+See [EDB private image registries](private_registries.md)
+for details on accessing the images.
+
+### Kubernetes architecture
+
+Some of the points of the
+[PG4K document on Kubernetes architecture](/postgres_for_kubernetes/latest/architecture/)
+are reproduced here. See the PG4K documentation for details.
+
+Kubernetes natively provides the possibility to span separate physical locations.
+These physical locations are also known as data centers, failure zones, or, more frequently, *availability
+zones*. They are connected to each other by way of redundant, low-latency, private network
+connectivity.
+
+Being a distributed system, the recommended minimum number of availability zones
+for a *Kubernetes cluster* is three. This minimum makes the control plane
+resilient to the failure of a single zone. This means that each data center is
+active at any time and can run workloads simultaneously.
+
+You can install EDB Postgres Distributed for Kubernetes in a
+[single Kubernetes cluster](#single-kubernetes-cluster)
+or across
+[multiple Kubernetes clusters](#multiple-kubernetes-clusters).
+
+### Single Kubernetes cluster
+
+A multi-availability-zone Kubernetes architecture is typical of Kubernetes
+services managed by cloud providers. Such an architecture enables the EDB Postgres Distributed for Kubernetes
+and the EDB Postgres for Kubernetes operators to schedule workloads and nodes across availability
+zones, considering all zones active.
+
+![Kubernetes cluster spanning over 3 independent data centers](./images/k8s-architecture-3-az.png)
+
+PGD clusters can be deployed in a single Kubernetes cluster and take advantage
+of Kubernetes availability zones to enable high-availability architectures,
+including the Always On recommended architectures.
+
+You can realize the *Always On Single Location* architecture shown in
+[Choosing your architecture](/pgd/latest/architectures/) in the PGD documentation on
+a single Kubernetes cluster with three availability zones.
+
+![Always On Single Region](./images/always_on_1x3_updated.png)
+
+The EDB Postgres Distributed for Kubernetes operator can control the scheduling of pods (that is, which pods go
+to which data center) using affinity, tolerations, and node selectors, as is the
+case with EDB Postgres for Kubernetes. Individual scheduling controls are available for proxies as well
+as nodes.
+
+See the
+[Kubernetes documentation on scheduling](https://kubernetes.io/docs/concepts/scheduling-eviction/),
+and [Scheduling](/postgres_for_kubernetes/latest/scheduling/) in the EDB Postgres for Kubernetes documentation
+for more information.
+
+### Multiple Kubernetes clusters
 
-The PostgreSQL instances created by the `Cluster` can be configured in the
-[`.spec.cnp` section](api_reference.md#CnpConfiguration).
+PGD clusters can also be deployed in multiple Kubernetes clusters that can
+reliably communicate with each other.
 
-## Single Kubernetes cluster
+![Multiple Kubernetes clusters](./images/k8s-architecture-multi.png)
 
-EDB Postgres Distributed can be executed inside a single Kubernetes cluster.
+[Always On multi-location PGD architectures](https://www.enterprisedb.com/docs/pgd/latest/architectures/)
+can be realized on multiple Kubernetes clusters that meet the connectivity
+requirements.
 
-## Multiple Kubernetes clusters
+For more information, see ["Connectivity"](connectivity.md).
 
-EDB Postgres Distributed for Kubernetes can also be deployed in different
-Kubernetes clusters that can reliably communicate with each other.
-More information can be found in the ["Connectivity"](connectivity.md) section.
+!!! Note Regions and availability zones 
+    When creating Kubernetes clusters in different regions or availability zones for cross-regional replication, 
+    ensure the clusters can communicate with each other by enabling network connectivity. Specifically, every service created with a `-node` or `-group` suffix must be discoverable by all other `-node` and `-group` services. You can achieve this by deploying a network connectivity application like 
+    [Submariner](https://submariner.io/) on every cluster. 

product_docs/docs/postgres_distributed_for_kubernetes/1/backup.mdx

@@ -0,0 +1,144 @@
+---
+title: 'Backup on object stores'
+originalFilePath: 'src/backup.md'
+---
+
+EDB Postgres Distributed for Kubernetes supports *online/hot backup* of
+PGD clusters through physical backup and WAL archiving on an object store.
+This means that the database is always up (no downtime required) and that
+point-in-time recovery (PITR) is available.
+
+## Common object stores
+
+Multiple object stores are supported, such as AWS S3, Microsoft Azure Blob Storage,
+Google Cloud Storage, MinIO Gateway, or any S3-compatible provider.
+Given that EDB Postgres Distributed for Kubernetes configures the connection with object stores by relying on
+EDB Postgres for Kubernetes, see the [EDB Postgres for Kubernetes cloud provider support](/postgres_for_kubernetes/latest/backup_recovery/#cloud-provider-support)
+documentation for more information.
+
+!!! Important
+    The EDB Postgres for Kubernetes documentation's Cloud Provider configuration section is
+    available at `spec.backup.barmanObjectStore`. In EDB Postgres Distributed for Kubernetes examples, the object store section is at a 
+    different path: `spec.backup.configuration.barmanObjectStore`.
+
+## WAL archive
+
+WAL archiving is the process that sends WAL files to the object storage, and it's essential to
+execute online/hot backups or PITR.
+In EDB Postgres Distributed for Kubernetes, each PGD node is set up to archive WAL files in the object store independently.
+
+The WAL archive is defined in the PGD Group `spec.backup.configuration.barmanObjectStore` stanza,
+and is enabled as soon as a destination path and cloud credentials are set.
+You can choose to compress WAL files before they're uploaded and you can encrypt them.
+You can also enable parallel WAL archiving:
+
+```yaml
+apiVersion: pgd.k8s.enterprisedb.io/v1beta1
+kind: PGDGroup
+[...]
+spec:
+  backup:
+    configuration:
+      barmanObjectStore:
+        [...]
+        wal:
+          compression: gzip
+          encryption: AES256
+          maxParallel: 8
+```
+
+For more information, see the [EDB Postgres for Kubernetes WAL archiving](/postgres_for_kubernetes/latest/backup_recovery/#wal-archiving) documentation.
+
+## Scheduled backups
+
+Scheduled backups are the recommended way to configure your backup strategy in EDB Postgres Distributed for Kubernetes.
+When the PGD group `spec.backup.configuration.barmanObjectStore` stanza is configured, the operator selects one of the
+PGD data nodes as the elected backup node for which it creates a `Scheduled Backup` resource.
+
+The `.spec.backup.cron.schedule` field allows you to define a cron schedule specification, expressed
+in the [Go `cron` package format](https://pkg.go.dev/github.com/robfig/cron#hdr-CRON_Expression_Format).
+
+```yaml
+apiVersion: pgd.k8s.enterprisedb.io/v1beta1
+kind: PGDGroup
+[...]
+spec:
+  backup:
+    cron:
+      schedule: "0 0 0 * * *"
+      backupOwnerReference: self
+      suspend: false
+      immediate: true
+```
+
+You can suspend scheduled backups if necessary by setting `.spec.backup.cron.suspend` to `true`. Setting this setting 
+to `true` prevents any new backup from being scheduled.
+
+If you want to execute a backup as soon as the `ScheduledBackup` resource is created,
+set `.spec.backup.cron.immediate` to `true`.
+
+`.spec.backupOwnerReference` indicates the `ownerReference` to use
+in the created backup resources. The choices are:
+
+-   **none** — No owner reference for created backup objects.
+-   **self** — Sets the `ScheduledBackup` object as owner of the backup.
+-   **cluster** — Sets the cluster as owner of the backup.
+
+!!! Note
+    The EDB Postgres for Kubernetes `ScheduledBackup` object contains the `cluster` option to specify the
+    cluster to back up. This option is currently not supported by EDB Postgres Distributed for Kubernetes and is
+    ignored if specified.
+
+If an elected backup node is deleted, the operator transparently elects a new backup node
+and reconciles the `ScheduledBackup` resource accordingly.
+
+## Retention policies
+
+EDB Postgres Distributed for Kubernetes can manage the automated deletion of backup files from the backup
+object store using retention policies based on the recovery window.
+This process also takes care of removing unused WAL files and WALs associated with backups
+that are scheduled for deletion.
+
+You can define your backups with a retention policy of 30 days:
+
+```yaml
+apiVersion: pgd.k8s.enterprisedb.io/v1beta1
+kind: PGDGroup
+[...]
+spec:
+  backup:
+    configuration:
+      retentionPolicy: "30d"
+```
+
+For more information, see the [EDB Postgres for Kubernetes retention policies](/postgres_for_kubernetes/latest/backup_recovery/#retention-policies) in the EDB Postgres for Kubernetes documentation.
+
+!!! Important
+    Currently, the retention policy is applied only for the elected `Backup Node`
+    backups and WAL files. Given that each other PGD node also archives its own WALs
+    independently, it's your responsibility to manage the lifecycle of those WAL files,
+    for example by leveraging the object storage data retention policy.
+    Also, if you have an object storage data retention policy set up on every PGD node
+    directory, make sure it's not overlapping or interfering with the retention policy managed
+    by the operator.
+
+## Compression algorithms
+
+Backups and WAL files are uncompressed by default. However, multiple compression algorithms are
+supported. For more information, see the [EDB Postgres for Kubernetes compression algorithms](/postgres_for_kubernetes/latest/backup_recovery/#compression-algorithms) documentation.
+
+## Tagging of backup objects
+
+It's possible to specify tags as key-value pairs for the backup objects, namely base backups, WAL files, and history files.
+For more information, see the EDB Postgres for Kubernetes documentation about [tagging of backup objects](/postgres_for_kubernetes/latest/backup_recovery/#tagging-of-backup-objects).
+
+## On-demand backups of a PGD node
+
+A PGD node is represented as single-instance EDB Postgres for Kubernetes `Cluster` object.
+As such, if you need to, it's possible to request an on-demand backup
+of a specific PGD node by creating a EDB Postgres for Kubernetes `Backup` resource.
+To do that, see [EDB Postgres for Kubernetes on-demand backups](/postgres_for_kubernetes/latest/backup_recovery/#on-demand-backups) in the EDB Postgres for Kubernetes documentation.
+
+!!! Hint
+    You can retrieve the list of EDB Postgres for Kubernetes clusters that make up your PGD group
+    by running `kubectl get cluster -l k8s.pgd.enterprisedb.io/group=my-pgd-group -n my-namespace`.