snapshots clients background added for Azure and S3 (#2148)

This PR adds a paragraph to clarify the meaning of `clients` in the
context of the documents for Azure and S3 repositories.

We have received
[feedback](elastic/docs-feedback#45) for the
Azure repository document showing frustration as it wasn't clear what
the azure client is and if it's something external to Elastic that the
customer needs to take care of.

Closes elastic/docs-feedback#45

---------

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>

Author: eedugon

deploy-manage/tools/snapshot-and-restore/azure-repository.md

@@ -12,19 +12,21 @@ products:
 
 You can use [Azure Blob storage](https://docs.microsoft.com/en-us/azure/storage/blobs/storage-blobs-introduction) as a repository for [Snapshot and restore](../snapshot-and-restore.md).
 
+{{es}} uses an internal client module to connect to Azure Blob storage, referred to in this document as the *Azure client* or the *Azure repository client*. Clients are configured through a combination of [secure settings](../../security/secure-settings.md) defined in the {{es}} keystore, and [standard settings](/deploy-manage/stack-settings.md) defined in the `elasticsearch.yml` configuration file.
+
 ## Setup [repository-azure-usage]
 
 To enable Azure repositories, first configure an Azure repository client by specifying one or more settings of the form `azure.client.CLIENT_NAME.SETTING_NAME`. By default, `azure` repositories use a client named `default`, but you may specify a different client name when registering each repository.
 
-The only mandatory Azure repository client setting is `account`, which is a [secure setting](../../security/secure-settings.md) defined in the [{{es}} keystore](../../security/secure-settings.md). To provide this setting, use the `elasticsearch-keystore` tool on each node:
+The only mandatory setting for an Azure repository client is `account`, which is a [secure setting](../../security/secure-settings.md) defined in the {{es}} keystore. To provide this setting, use the `elasticsearch-keystore` tool on each node:
 
 ```sh
 bin/elasticsearch-keystore add azure.client.default.account
 ```
 
-If you adjust this setting after a node has started, call the [Nodes reload secure settings API](../../security/secure-settings.md) to reload the new value.
+If you adjust this setting after a node has started, call the [Nodes reload secure settings API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-nodes-reload-secure-settings) to reload the new value.
 
-You may define more than one client by setting their `account` values. For instance, to set the `default` client and another client called `secondary`, run the following commands on each node:
+You may define more than one client by setting their `account` values. For example, to set the `default` client and another client called `secondary`, run the following commands on each node:
 
 ```sh
 bin/elasticsearch-keystore add azure.client.default.account

deploy-manage/tools/snapshot-and-restore/s3-repository.md

@@ -18,6 +18,8 @@ If you are looking for a hosted solution of {{es}} on AWS, visit [https://www.el
 
 See [this video](https://www.youtube.com/watch?v=ACqfyzWf-xs) for a walkthrough of connecting an AWS S3 repository.
 
+{{es}} communicates with S3 through a dedicated S3 client module. Clients are configured through a combination of [secure settings](../../security/secure-settings.md) defined in the {{es}} keystore, and [standard settings](/deploy-manage/stack-settings.md) defined in `elasticsearch.yml`. If you don't provide explicit S3 client configuration, {{es}} will try to obtain credentials from the environment it's running in.
+
 ## Getting started [repository-s3-usage]
 
 To register an S3 repository, specify the type as `s3` when creating the repository. The repository defaults to using [ECS IAM Role](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-iam-roles.html) credentials for authentication. You can also use [Kubernetes service accounts](#iam-kubernetes-service-accounts) for authentication.
@@ -37,7 +39,7 @@ PUT _snapshot/my_s3_repository
 
 ## Client settings [repository-s3-client]
 
-The client that you use to connect to S3 has a number of settings available. The settings have the form `s3.client.CLIENT_NAME.SETTING_NAME`. By default, `s3` repositories use a client named `default`, but this can be modified using the [repository setting](#repository-s3-repository) `client`. For example, to use a client named `my-alternate-client`, register the repository as follows:
+The S3 client that you use to connect to S3 has a number of settings available. The settings have the form `s3.client.CLIENT_NAME.SETTING_NAME`. By default, `s3` repositories use a client named `default`, but this can be modified using the [repository setting](#repository-s3-repository) `client`. For example, to use an S3 client named `my-alternate-client`, register the repository as follows:
 
 ```console
 PUT _snapshot/my_s3_repository
@@ -50,7 +52,7 @@ PUT _snapshot/my_s3_repository
 }
 ```
 
-Most client settings can be added to the [`elasticsearch.yml`](/deploy-manage/stack-settings.md) configuration file with the exception of the secure settings, which you add to the {{es}} keystore. For more information about creating and updating the {{es}} keystore, see [Secure settings](../../security/secure-settings.md).
+Most S3 client settings can be added to the [`elasticsearch.yml`](/deploy-manage/stack-settings.md) configuration file with the exception of the secure settings, which you add to the {{es}} keystore. For more information about creating and updating the {{es}} keystore, see [Secure settings](../../security/secure-settings.md).
 
 For example, if you want to use specific credentials to access S3 then run the following commands to add these credentials to the keystore.
 
@@ -77,7 +79,7 @@ bin/elasticsearch-keystore remove s3.client.default.session_token
 
 Define the relevant secure settings in each node’s keystore before starting the node. The secure settings described here are all [reloadable](../../security/secure-settings.md#reloadable-secure-settings) so you may update the keystore contents on each node while the node is running and then call the [Nodes reload secure settings API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-nodes-reload-secure-settings) to apply the updated settings to the nodes in the cluster. After this API completes, {{es}} will use the updated setting values for all future snapshot operations, but ongoing operations may continue to use older setting values.
 
-The following list contains the available client settings. Those that must be stored in the keystore are marked as "secure" and are **reloadable**; the other settings belong in the [`elasticsearch.yml`](/deploy-manage/stack-settings.md) file.
+The following list contains the available S3 client settings. Those that must be stored in the keystore are marked as "secure" and are **reloadable**; the other settings belong in the [`elasticsearch.yml`](/deploy-manage/stack-settings.md) file.
 
 `region`
 :   Specifies the region to use. When set, determines the signing region and regional endpoint to use, unless the endpoint is overridden via the `endpoint` setting. If not set, {{es}} will attempt to determine the region automatically using the AWS SDK.