Since admin requests aren't routed through the cache frontend, the global...

Since admin requests aren't routed through the cache frontend, the global variable isn't available. Use defines for these overrides instead.

Unfortunately does mean that settings are split, but alternatives weren't appealing:
* store settings into an option via the front-end proxy (front-end writes are bad)
* store in Redis (could lose the option, randomly revealing a UI)
* pass all wp-admin requests through the proxy with early bailing to avoid breakage seems overly complicated and fragile/prone to bugs.

wp-redis-cache/wp-redis-cache.php

@@ -123,7 +123,7 @@ class WP_Redis_Cache {
 	private $ns = 'wp-redis-cache';
 
 	/**
-	 *
+	 * Singleton instantiation
 	 */
 	public static function get_instance() {
 		if ( ! is_a( self::$__instance, __CLASS__ ) ) {
@@ -161,12 +161,9 @@ class WP_Redis_Cache {
 	 * @return null
 	 */
 	public function register_ui() {
-		// If cache life is set globally, don't show the UI
-		global $wp_redis_cache_config;
-		if ( is_array( $wp_redis_cache_config ) &&
-			( isset( $wp_redis_cache_config['cache_duration' ] ) || isset( $wp_redis_cache_config['unlimited' ] ) )
-		) {
-			return;
+		// Don't show UI
+		if ( defined( 'WP_REDIS_CACHE_HIDE_UI' ) && WP_REDIS_CACHE_HIDE_UI ) {
+			return
 		}
 
 		add_options_page( 'WP Redis Cache', 'WP Redis Cache', 'manage_options', $this->ns, array( $this, 'render_ui' ) );
@@ -232,10 +229,14 @@ class WP_Redis_Cache {
 			);
 
 			// Override default connection settings with global values, when present
-			global $wp_redis_cache_config;
-			if ( is_array( $wp_redis_cache_config ) ) {
-				$_redis_settings = array_intersect( $wp_redis_cache_config, $redis_settings );
-				$redis_settings = wp_parse_args( $_redis_settings, $redis_settings );
+			if ( defined( 'WP_REDIS_CACHE_REDIS_HOST' ) ) {
+				$redis_settings['host'] = WP_REDIS_CACHE_REDIS_HOST;
+			}
+			if ( defined( 'WP_REDIS_CACHE_REDIS_PORT' ) ) {
+				$redis_settings['port'] = WP_REDIS_CACHE_REDIS_PORT;
+			}
+			if ( defined( 'WP_REDIS_CACHE_REDIS_DB' ) ) {
+				$redis_settings['database'] = WP_REDIS_CACHE_REDIS_DB;
 			}
 
 			$permalink = get_permalink( $post->ID );