Add RDBMS backup documentation

docs/guides/migrating-from-camunda-7/conceptual-differences.md

@@ -120,9 +120,15 @@ With Camunda 8 you deploy:
 
 - Your Spring Boot application with all custom code and the Zeebe client embedded. This application is typically scaled to at least two instances (for resilience)
 - The Zeebe Broker, typically scaled to at least three instances (for resilience)
-- An elastic database (for Operate, Tasklist, and Optimize)
+- A database (for Operate, Tasklist and the C8 REST API). Here you can choose between:
+  - Relational database. Currently supported are: H2, PostgreSQL, MariaDB, and Oracle.
+  - Elasticsearch
+- An elastic database (for Operate)
 - Optimize, Operate, and Tasklist (each one is a Java application). You can scale those applications to increase availability if you want.
 
+:::note
+TODO: Adjust Image to RDBMS and Elasticsearch
+:::
 ![Camunda 7 vs Camunda 8 Deployment View](../img/camunda7-vs-camunda8-deployment-view.png)
 
 Camunda 8 deployments happen within Kubernetes. There are [Helm charts available](self-managed/setup/overview.md) if you want to run Camunda 8 Self-Managed.

docs/self-managed/concepts/databases/overview.md

@@ -0,0 +1,44 @@
+---
+id: overview
+title: "Overview"
+description: "An overview about possible databases"
+---
+
+To service applications like Operate, Tasklist and the Camunda REST API with data, Camunda 8 requires a database. This database stores data for all processes, processInstances, decisions, tasks, users etc.
+
+Camunda 8 supports the following databases:
+
+## Document based databases
+
+TODO: Add more text about behavior and limitations?
+
+Document based databases like ElasticSearch and OpenSearch
+
+## Relational databases
+
+TODO: Decide which minimal version is supported
+
+Currently, the following relational databases are officially supported:
+
+- PostgreSQL (17+)
+- Oracle (23+)
+- MariaDB (11.6+)
+- H2 (2.3)
+
+To use and configure an RDBMS as storage backend, follow the instructions in the [Configuration](./relational-db/configuration.md) section.
+
+### Limitations
+
+When using a relational database as storage backend, the following limitations apply:
+
+#### Variables
+
+[The Camunda REST API](./../../../../apis-tools/camunda-api-rest/camunda-api-rest-overview) allows to fetch and filter for [Variables](./../../../../apis-tools/camunda-api-rest/specifications/get-variable).
+To keep the API performant, the following comparison operations are only applied on the first 4000 characters of a String or JSON variable value:
+
+- equals
+- notEquals
+- in
+- notIn
+
+The LIKE operator is not affected by this limitation.

docs/self-managed/concepts/databases/relational-db/configuration.md

@@ -0,0 +1,104 @@
+---
+id: database-configuration
+title: "Configuration"
+---
+
+## Installation
+
+To enable Camunda to use a relational database, two main configuration steps are required:
+
+1. Add the RDBMS [Exporter](./../../exporters.md) to the Zeebe broker configuration.
+2. Enable the RDBMS as primary database for [Camunda REST API](./../../../../apis-tools/camunda-api-rest/camunda-api-rest-overview)
+3. Configure the database connection. This is done by configuring the Spring datasource.
+
+```yaml
+# enable the exporter
+zeebe:
+  broker:
+    exporters:
+      rdbms:
+        className: RdbmsExporter
+        args:
+          # see Configuration section for configuration options
+
+# set the RDBMS as primary database for Camunda REST API
+camunda:
+  database:
+    type: rdbms
+    url: jdbc:postgresql:camunda # example for a local PostgreSQL database with schema "camunda"
+    username: camunda
+    password: camunda
+```
+
+The RDBMS [Exporter](./../../exporters.md) configuration can be enabled in addition to other [Exporter](./../../exporters.md) as well. Note, that adding more exporters, can slow down the cluster.
+
+#### DB Schema management
+
+By default, Camunda will automatically create and update the database schema on startup. For this it uses the tool [Liquibase](https://www.liquibase.com/). In addition to the Camunda core tables, Liquibase will create the two tables `DATABASECHANGELOG` and `DATABASECHANGELOGLOCK`. These tables must not be changed or updated.
+
+If the target database schema is not empty, it sometimes can be useful to define a prefix for the Camunda tables. This can be done by setting the following property in the configuration:
+
+```yaml
+camunda.database.index-prefix: c8_
+```
+
+To disable the automatic schema management, set the following property in the configuration:
+
+```yaml
+camunda.database.auto-ddl: false
+```
+
+Native SQL scripts for all supported databases can be found in the Camunda distribution (TODO:LINK). These scripts can be used to create the schema manually.
+
+### Database privileges
+
+To use Camunda with the RDBMS, the configured database user must have the following privileges on the all Camunda tables (the actual privilege names might depend on the database vendor):
+
+- SELECT
+- INSERT
+- UPDATE
+- DELETE
+
+Optionally, to enable the automatic schema management by Camunda and [Liquibase](https://www.liquibase.com/), the additional privileges must have been granted before the first start of any Camunda instance:
+
+- CREATE
+- ALTER
+- DROP
+
+Optionally, to enable the PURGE (TODO: Link) feature of the RDBMS Exporter, the following privilege must be granted to the camunda database user on all Camunda tables:
+
+- TRUNCATE
+
+## Configuration
+
+### Database configuration
+
+Camunda RDBMS database configuration reference:
+
+| Property name                       | Description                                                                                                                                                                    | Default setting |
+| ----------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | --------------- |
+| camunda.database.url                | The JDBC connection url of the database                                                                                                                                        | _empty_         |
+| camunda.database.user               | The username for the database connection                                                                                                                                       | _empty_         |
+| camunda.database.password           | The password for the database connection                                                                                                                                       | _empty_         |
+| camunda.database.auto-ddl           | If the Liquibase schemamanagement should be used or not. If not, the DBA has to install the schema from available [scripts](#db-schema-management)                             | true            |
+| camunda.database.index-prefix       | A custom prefix for all camunda related database objects.                                                                                                                      | '' (empty)      |
+| camunda.database.database-vendor-id | Camunda uses vendor auto-detection vendor specific functions. With this property this auto-detection can be overridden. Possible values: _h2_, _mariadb_, _oracle_, _postgres_ | _empty_         |
+
+### Exporter Configuration
+
+The RDBMS Exporter can be configured in the `args` section of the exporter configuration:
+
+```yaml
+# enable the exporter
+zeebe.broker.exporters:
+  rdbms:
+    args:
+      propertyName: propertyValue
+```
+
+The following configuration options are available:
+
+| Property name | Description                                                                                                           | Default setting |
+| ------------- | --------------------------------------------------------------------------------------------------------------------- | --------------- |
+| flushInterval | The maximum time an exported record waits in the flush queue before being flushed and committed to the database       | 500 (ms)        |
+| maxQueueSize  | The maximum number of records that can be added to the flush queue before being flushed and committed to the database | 1000            |

docs/self-managed/operational-guides/backup-restore/backup-and-restore.md

@@ -24,6 +24,8 @@ Zeebe stores its backup to an external storage and must be configured before the
 
 ### Backup process
 
+#### Backups using ElasticSearch
+
 The backup of each component and the backup of a Camunda 8 cluster is identified by an id. This means a backup `x` of Camunda 8 consists of backup `x` of Zeebe, backup `x` of Optimize, backup `x` of Operate, and backup `x` of Tasklist. The backup ID must be an integer and greater than the previous backups.
 
 :::note
@@ -62,9 +64,29 @@ By default, the indices are prefixed with `zeebe-record`. If you have configured
 If any of the steps above fail, you may have to restart with a new backup id. Ensure exporting is resumed if the backup process force quits in the middle of the process.
 :::
 
+#### Backups using an RDBMS
+
+When using an RDBMS like PostgreSQL, Oracle or MariaDB, the backups of Zeebe and the database have to be taken separately and also depend on the database system.
+
+The backup of Zeebe is identified by an id `x`. The backup ID must be an integer and greater than the previous backups.
+
+:::note
+We recommend using the timestamp as the backup id.
+:::
+
+To back up a Camunda cluster using an RDBMS, follow these steps:
+
+1. Soft pause exporting in Zeebe. See [Zeebe management API](/self-managed/zeebe-deployment/operations/management-api.md).
+2. Take a backup of the relational database. See the documentation of the database system you are using. It is recommended to identify the database backup with the same backupId `x` as will be used for the Zeebe backup.
+3. Take a backup `x` of Zeebe. See [how to take a Zeebe backup](/self-managed/operational-guides/backup-restore/zeebe-backup-and-restore.md).
+4. Wait until the backup `x` of Zeebe is completed before proceeding. See [how to monitor a Zeebe backup](/self-managed/operational-guides/backup-restore/zeebe-backup-and-restore.md).
+   Resume exporting in Zeebe. See [Zeebe management API](/self-managed/zeebe-deployment/operations/management-api.md).
+
 ### Restore
 
-To restore a Camunda 8 cluster from a backup, all components must be restored from their backup corresponding to the same backup id:
+#### Restoring using ElasticSearch
+
+To restore an ElasticSearch based Camunda 8 cluster from a backup, all components must be restored from their backup corresponding to the same backup id:
 
 1. Start Zeebe, Operate, Tasklist, and Optimize. (To ensure templates/aliases etc. are created)
 2. Confirm proper configuration (such as shards, replicas count, etc.)
@@ -74,3 +96,11 @@ To restore a Camunda 8 cluster from a backup, all components must be restored fr
 6. Restore `zeebe-records*` indices from Elasticsearch snapshot.
 7. Restore [Zeebe](/self-managed/operational-guides/backup-restore/zeebe-backup-and-restore.md).
 8. Start Zeebe, Operate, Tasklist, and Optimize.
+
+#### Restoring using an RDBMS
+
+To restore an RDBMS based Camunda 8 cluster from a backup, follow these steps:
+
+1. Restore the relational database backup into an empty database.
+2. Restore [Zeebe](/self-managed/operational-guides/backup-restore/zeebe-backup-and-restore.md).
+3. Start Zeebe, Operate, Tasklist, and Optimize.

sidebars.js

@@ -1085,10 +1085,24 @@ module.exports = {
         {
           "Multi-region": ["self-managed/concepts/multi-region/dual-region"],
         },
+        {
+          Databases: [
+            "self-managed/concepts/databases/overview",
+            {
+              Elasticsearch: [
+                "self-managed/concepts/databases/elasticsearch/elasticsearch-privileges",
+                "self-managed/concepts/databases/elasticsearch/opensearch-privileges",
+              ],
+            },
+            {
+              "Relational databases": [
+                "self-managed/concepts/databases/relational-db/database-configuration",
+              ],
+            },
+          ],
+        },
         "self-managed/concepts/multi-tenancy",
         "self-managed/concepts/mapping-rules",
-        "self-managed/concepts/elasticsearch-privileges",
-        "self-managed/concepts/opensearch-privileges",
       ],
     },
     {