feat(config): allow to override some config values by hostname

build/psalm-baseline.xml

@@ -3522,10 +3522,6 @@
       <code><![CDATA[$this->delete($key)]]></code>
       <code><![CDATA[$this->set($key, $value)]]></code>
     </InvalidOperand>
-    <UndefinedVariable>
-      <code><![CDATA[$CONFIG]]></code>
-      <code><![CDATA[$CONFIG]]></code>
-    </UndefinedVariable>
   </file>
   <file src="lib/private/Console/Application.php">
     <NoInterfaceProperties>

config/config.sample.php

@@ -45,6 +45,17 @@
 	 */
 	'instanceid' => '',
 
+	/**
+	 * This is a unique identifier for your server.
+	 * It is useful when your Nextcloud instance is spread between different servers.
+	 * Once it's set it shouldn't be changed.
+	 *
+	 * Value must be an integer, comprised between 0 and 1023.
+	 *
+	 * This value should be overriden by hostname in $CONFIG_HOSTNAME
+	 */
+	'serverid' => -1,
+
 	/**
 	 * The salt used to hash all passwords, auto-generated by the Nextcloud
 	 * installer. (There are also per-user salts.) If you lose this salt, you lose
@@ -2813,3 +2824,18 @@
 	 */
 	'enable_lazy_objects' => true,
 ];
+
+/**
+ * CONFIG_HOSTNAME allows to set specific configuration value on specific hosts.
+ * It should be used when configuration is stored on a shared filesystem between several servers.
+ *
+ * Only options listed in \OC\Config::HOST_OVERRIDE_CONFIG can be defined here.
+ */
+$CONFIG_HOSTNAME = [
+	'hostname_a' => [
+		'serverid' => 42,
+	],
+	'hostname_b' => [
+		'serverid' => 43,
+	],
+];

lib/private/Config.php

@@ -15,6 +15,10 @@
  */
 class Config {
 	public const ENV_PREFIX = 'NC_';
+	// List configurations that can be overriden based on server hostname
+	private const HOST_OVERRIDE_CONFIG = [
+		'serverid',
+	];
 
 	/** @var array Associative array ($key => $value) */
 	protected $cache = [];
@@ -199,7 +203,7 @@ private function readData() {
 
 		// Include file and merge config
 		foreach ($configFiles as $file) {
-			unset($CONFIG);
+			$CONFIG = $CONFIG_HOSTNAME = null;
 
 			// Invalidate opcache (only if the timestamp changed)
 			if (function_exists('opcache_invalidate')) {
@@ -226,6 +230,10 @@ private function readData() {
 			}
 
 			try {
+				/**
+				 * @var ?array $CONFIG
+				 * @var ?array $CONFIG_HOSTNAME
+				 */
 				include $file;
 			} finally {
 				// Close the file pointer and release the lock
@@ -241,9 +249,20 @@ private function readData() {
 				}
 				throw new \Exception($errorMessage);
 			}
-			if (isset($CONFIG) && is_array($CONFIG)) {
+			if (is_array($CONFIG)) {
 				$this->cache = array_merge($this->cache, $CONFIG);
 			}
+			if (is_array($CONFIG_HOSTNAME) && !empty($CONFIG_HOSTNAME)) {
+				$hostname = gethostname();
+				if (isset($CONFIG_HOSTNAME[$hostname]) && is_array($CONFIG_HOSTNAME[$hostname])) {
+					$filteredConfig = array_filter(
+						$CONFIG_HOSTNAME[$hostname],
+						fn ($key) => in_array($key, self::HOST_OVERRIDE_CONFIG),
+						ARRAY_FILTER_USE_KEY,
+					);
+					$this->cache = array_merge($this->cache, $filteredConfig);
+				}
+			}
 		}
 
 		// grab any "NC_" environment variables

lib/private/Snowflake/Generator.php

@@ -10,6 +10,7 @@
 namespace OC\Snowflake;
 
 use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\IConfig;
 use OCP\Snowflake\IGenerator;
 use Override;
 
@@ -23,6 +24,7 @@
 final class Generator implements IGenerator {
 	public function __construct(
 		private readonly ITimeFactory $timeFactory,
+		private readonly IConfig $config,
 	) {
 	}
 
@@ -100,7 +102,10 @@ private function getCurrentTime(): array {
 	}
 
 	private function getServerId(): int {
-		return crc32(gethostname() ?: random_bytes(8));
+		$serverid = $this->config->getSystemValueInt('serverid', -1);
+		return $serverid > 0
+			? $serverid
+			: crc32(gethostname() ?: random_bytes(8));
 	}
 
 	private function isCli(): bool {

tests/lib/Snowflake/GeneratorTest.php

@@ -13,6 +13,7 @@
 use OC\Snowflake\Decoder;
 use OC\Snowflake\Generator;
 use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\IConfig;
 use OCP\Snowflake\IGenerator;
 use PHPUnit\Framework\Attributes\DataProvider;
 use Test\TestCase;
@@ -22,12 +23,17 @@
  */
 class GeneratorTest extends TestCase {
 	private Decoder $decoder;
+	private IConfig|MockObject $config;
 
 	public function setUp():void {
 		$this->decoder = new Decoder();
+		$this->config = $this->createMock(IConfig::class);
+		$this->config->method('getSystemValueInt')
+			->with('serverid')
+			->willReturn(42);
 	}
 	public function testGenerator(): void {
-		$generator = new Generator(new TimeFactory());
+		$generator = new Generator(new TimeFactory(), $this->config);
 		$snowflakeId = $generator->nextId();
 		$data = $this->decoder->decode($generator->nextId());
 
@@ -45,6 +51,9 @@ public function testGenerator(): void {
 
 		// Check CLI
 		$this->assertTrue($data['isCli']);
+
+		// Check serverId
+		$this->assertEquals(42, $data['serverId']);
 	}
 
 	#[DataProvider('provideSnowflakeData')]
@@ -53,11 +62,12 @@ public function testGeneratorWithFixedTime(string $date, int $expectedSeconds, i
 		$timeFactory = $this->createMock(ITimeFactory::class);
 		$timeFactory->method('now')->willReturn($dt);
 
-		$generator = new Generator($timeFactory);
+		$generator = new Generator($timeFactory, $this->config);
 		$data = $this->decoder->decode($generator->nextId());
 
 		$this->assertEquals($expectedSeconds, ($data['createdAt']->format('U') - IGenerator::TS_OFFSET));
 		$this->assertEquals($expectedMilliseconds, (int)$data['createdAt']->format('v'));
+		$this->assertEquals(42, $data['serverId']);
 	}
 
 	public static function provideSnowflakeData(): array {