diff --git a/includes/classes/Command.php b/includes/classes/Command.php
index b3eda79261..f0aff11d70 100644
--- a/includes/classes/Command.php
+++ b/includes/classes/Command.php
@@ -1482,6 +1482,65 @@ public function settings_reset( $args, $assoc_args ) {
 		WP_CLI::line( esc_html__( 'Settings deleted.', 'elasticpress' ) );
 	}
 
+	/**
+	 * Migrate content from an Elasticsearch server to another..
+	 *
+	 * ## OPTIONS
+	 *
+	 * --target=<target_host>
+	 * : The target host full URL
+	 *
+	 * @since 4.2.0
+	 *
+	 * @param array $args Positional CLI args.
+	 * @param array $assoc_args Associative CLI args.
+	 */
+	public function migrate( $args, $assoc_args ) {
+		$source_host = trailingslashit( Utils\get_host( true ) );
+		$target_host = esc_url_raw( trim( $assoc_args['target'] ) );
+
+		$set_target_as_host = function () use ( $target_host ) {
+			return $target_host;
+		};
+
+		WP_CLI::line( esc_html__( 'Switching context to target server.', 'elasticpress' ) );
+		add_filter( 'ep_host', $set_target_as_host );
+
+		// Check if server is available and then send the mapping.
+		$this->connect_check();
+		$this->put_mapping_helper( $args, [ 'network-wide' => true ] );
+
+		$index_names = $this->get_index_names();
+		foreach ( $index_names as $index ) {
+			WP_CLI::line(
+				sprintf(
+					/* translators: Index name */
+					esc_html__( 'Reindexing %s...', 'elasticpress' ),
+					esc_html( $index )
+				)
+			);
+			$request = Elasticsearch::factory()->reindex( $index, $source_host, $target_host );
+			if ( is_wp_error( $request ) ) {
+				WP_CLI::error(
+					sprintf(
+						/* translators: 1. Error message, 2. Error code */
+						esc_html__( '%1$s (Code %2$s)', 'elasticpress' ),
+						$request->get_error_message(),
+						$request->get_error_code()
+					)
+				);
+			} else {
+				WP_CLI::log( var_export( $request, true ) );
+			}
+			// @todo Output details of successful reindexes.
+		}
+
+		update_site_option( 'ep_host', $target_host );
+		remove_filter( 'ep_host', $set_target_as_host );
+
+		WP_CLI::success( esc_html__( 'Done.', 'elasticpress' ) );
+	}
+
 	/**
 	 * Print an HTTP response.
 	 *
diff --git a/includes/classes/Elasticsearch.php b/includes/classes/Elasticsearch.php
index 4081c746da..95cc97d083 100644
--- a/includes/classes/Elasticsearch.php
+++ b/includes/classes/Elasticsearch.php
@@ -1537,6 +1537,68 @@ public function add_elasticpress_version_to_user_agent( $user_agent ) {
 		return $user_agent;
 	}
 
+	/**
+	 * Reindex content
+	 *
+	 * @since 4.2.0
+	 *
+	 * @param string $index  Index name
+	 * @param string $source Source host URL
+	 * @return WP_Error|string
+	 */
+	public function reindex( $index, $source ) {
+		$parsed_url = wp_parse_url( $source );
+
+		$scheme   = isset( $parsed_url['scheme'] ) ? $parsed_url['scheme'] . '://' : '';
+		$host     = isset( $parsed_url['host'] ) ? $parsed_url['host'] : '';
+		$port     = isset( $parsed_url['port'] ) ? ':' . $parsed_url['port'] : ':80';
+		$user     = isset( $parsed_url['user'] ) ? $parsed_url['user'] : '';
+		$pass     = isset( $parsed_url['pass'] ) ? ':' . $parsed_url['pass'] : '';
+		$pass     = ( $user || $pass ) ? "$pass@" : '';
+		$path     = isset( $parsed_url['path'] ) ? $parsed_url['path'] : '';
+		$query    = isset( $parsed_url['query'] ) ? '?' . $parsed_url['query'] : '';
+		$fragment = isset( $parsed_url['fragment'] ) ? '#' . $parsed_url['fragment'] : '';
+		$source   = "$scheme$user$pass$host$port$path$query$fragment";
+
+		$content = [
+			'max_docs' => 1000,
+			'source'   => [
+				'remote' => [
+					'host' => 'http://elasticsearch5:9200/', // @todo untrailingslashit( $source ),
+				],
+				'index'  => $index,
+			],
+			'dest'     => [
+				'index' => $index,
+			],
+		];
+
+		$request_args = [
+			'body'    => wp_json_encode( $content ),
+			'method'  => 'POST',
+			'headers' => [
+				'Content-Type' => 'application/json',
+			],
+		];
+
+		$request = $this->remote_request( '_reindex', $request_args, [], 'reindex' );
+
+		if ( is_wp_error( $request ) ) {
+			return $request;
+		}
+
+		$response_code = absint( wp_remote_retrieve_response_code( $request ) );
+		$is_valid_res  = ( $response_code >= 200 && $response_code <= 299 );
+
+		$response_body = wp_remote_retrieve_body( $request );
+
+		if ( ! $is_valid_res ) {
+			return new \WP_Error( $response_code, $response_body );
+		}
+
+		return $response_body;
+	}
+
 	/**
 	 * Query logging. Don't log anything to the queries property when
 	 * WP_DEBUG is not enabled. Calls action 'ep_add_query_log' if you