Adds documentation page for remote-backed storage (#1179)

* Created page based on structure of PR 1163

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Added prerequisite steps for enabling the feature and its dependency

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Adding more

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Adding more content

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Finishing up and ready for tech review

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Moved page per dev request

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Fixed header and changed heading sizes

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Ready for tech review

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

* Added link to segment replication

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

Signed-off-by: JeffH-AWS <jeffhuss@amazon.com>

_opensearch/remote.md

@@ -0,0 +1,120 @@
+---
+layout: default
+title: Remote-backed storage
+nav_order: 19
+---
+
+# Remote-backed storage
+
+Remote-backed storage offers OpenSearch users a new way to protect against data loss by automatically creating backups of all index transactions and sending them to a supported cloud storage service. In order to expose this feature, segment replication must also be enabled. See [Segment replication]({{site.url}}{{site.baseurl}}/opensearch/segment-replication/) for additional information.
+
+Remote-backed storage is an experimental feature. Therefore, we do not recommend the use of remote-backed storage in a production environment. For updates on the progress of remote-backed storage, or if you want leave feedback that could help improve the feature, refer to the issue on [GitHub](https://github.com/opensearch-project/OpenSearch/issues/1968).
+{: .note}
+
+## Enable the feature
+
+In order to create new indexes with remote-backed storage enabled, you must first enable these features by adding the correct properties to `run.gradle` before building OpenSearch. See the [developer guide](https://github.com/opensearch-project/OpenSearch/blob/main/DEVELOPER_GUIDE.md) for information about how Gradle is used to build OpenSearch.
+
+Add the following properties to `run.gradle` to enable the feature:
+
+```bash
+testClusters {
+  runTask {
+    testDistribution = 'archive'
+    if (numZones > 1) numberOfZones = numZones
+    if (numNodes > 1) numberOfNodes = numNodes
+    systemProperty 'opensearch.experimental.feature.replication_type.enabled', 'true'
+    systemProperty 'opensearch.experimental.feature.remote_store.enabled', 'true'
+  }
+}
+```
+
+Segment replication must also be enabled in order to use remote-backed storage.
+{: .note}
+
+After building OpenSearch with these properties, you must enable the feature for all nodes in your cluster. This can be done by modifying a `config/jvm.options`, or by defining `OPENSEARCH_JAVA_OPS` from the command line.
+
+### Option 1: Modify jvm.options
+
+Add the following lines to `config/jvm.options` before starting the OpenSearch process to enable the feature and its dependency:
+
+```
+-Dopensearch.experimental.feature.replication_type.enabled=true
+-Dopensearch.experimental.feature.remote_store.enabled=true
+```
+
+Run OpenSearch
+
+```bash
+./bin/opensearch
+```
+
+### Option 2: Enable from an environment variable
+
+As an alternative to directly modifying `config/jvm.options`, you can define the properties by using an environment variable. This can be done in a single command when you start OpenSearch or by defining the variable with `export`.
+
+To add these flags in-line when starting OpenSearch:
+
+```bash
+OPENSEARCH_JAVA_OPTS="-Dopensearch.experimental.feature.replication_type.enabled=true -Dopensearch.experimental.feature.remote_store.enabled=true" ./opensearch-{{site.opensearch_version}}/bin/opensearch
+```
+
+If you want to define the environment variable separately, prior to running OpenSearch:
+
+```bash
+export OPENSEARCH_JAVA_OPTS="-Dopensearch.experimental.feature.replication_type.enabled=true -Dopensearch.experimental.feature.remote_store.enabled=true"
+./bin/opensearch
+```
+
+## Register a remote repository
+
+Now that your deployment is running with the feature flags enabled, the next step is to register a remote repository where backups will be stored. See [Register repository]({{site.url}}{{site.baseurl}}/opensearch/snapshots/snapshot-restore#register-repository) for more information.
+
+## Create an index
+
+Remote-backed storage is enabled for an index when it is created. This feature cannot be enabled for indexes that already exist.
+
+When creating the index, include the `remote_store` property to enable the feature and specify a target repository:
+
+```bash
+curl -X PUT "https://localhost:9200/my-index?pretty" -ku admin:admin -H 'Content-Type: application/json' -d'
+{
+  "settings": {
+    "index": {
+      "number_of_shards": 1,
+      "number_of_replicas": 0,
+      "replication": {
+        "type": "SEGMENT"
+      },
+      "remote_store": {
+        "enabled": true,
+        "repository": "my-repo-1"
+      }
+    }
+  }
+}
+'
+```
+
+All data that is added to the index will also be uploaded to the remote storage once it is committed.
+
+### Restoring from a backup
+
+To restore an index from a remote backup, such as in the event of a node failure, you must first close the index:
+
+```bash
+curl -X POST "https://localhost:9200/my-index/_close" -ku admin:admin
+```
+
+Restore the index from the backup stored on the remote repository:
+
+```bash
+curl -X POST "https://localhost:9200/_remotestore/_restore" -ku admin:admin -H 'Content-Type: application/json' -d'
+{
+  "indices": ["my-index"]
+}
+'
+```
+
+If the security plugin is enabled, a user must have the `cluster:admin/remotestore/restore` permission. See [Access control](/security-plugin/access-control/index/) for information about configuring user permissions.
+{: .note}