Magento 2.4.4 READONLY You can't write against a read-only replica

Question

The website keeps going down throwing error.

{"0":"READONLY You can't write against a read-only replica.","1":"#1 Cm\RedisSession\Handler->read() called at [vendor/magento/framework/Session/SaveHandler/Redis.php:98]\n#2 Magento\Framework\Session\SaveHandler\Redis->read() called at [vendor/magento/framework/Session/SaveHandler.php:212]\n#3 Magento\Framework\Session\SaveHandler->callSafely() called at [vendor/magento/framework/Session/SaveHandler.php:125]\n#4 Magento\Framework\Session\SaveHandler->read()\n#5 session_start() called at [vendor/magento/framework/Session/SessionManager.php:204]\n#6 Magento\Framework\Session\SessionManager->start() called at [generated/code/Magento/Backend/Model/Auth/Session/Interceptor.php:122]\n#7 Magento\Backend\Model\Auth\Session\Interceptor->start() called at [vendor/magento/framework/Session/SessionManager.php:141]\n#8 Magento\Framework\Session\SessionManager->__construct() called at [vendor/magento/module-backend/Model/Auth/Session.php:102]\n#9 Magento\Backend\Model\Auth\Session->__construct() called at [generated/code/Magento/Backend/Model/Auth/Session/Interceptor.php:14]\n#10 Magento\Backend\Model\Auth\Session\Interceptor->__construct() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:121]\n#11 Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:66]\n#12 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create() called at [vendor/magento/framework/ObjectManager/ObjectManager.php:70]\n#13 Magento\Framework\ObjectManager\ObjectManager->get() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:170]\n#14 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:276]\n#15 Magento\Framework\ObjectManager\Factory\AbstractFactory->getResolvedArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:239]\n#16 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:34]\n#17 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:59]\n#18 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create() called at [vendor/magento/framework/ObjectManager/ObjectManager.php:70]\n#19 Magento\Framework\ObjectManager\ObjectManager->get() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:170]\n#20 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:276]\n#21 Magento\Framework\ObjectManager\Factory\AbstractFactory->getResolvedArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:239]\n#22 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:34]\n#23 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:59]\n#24 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create() called at [vendor/magento/framework/ObjectManager/ObjectManager.php:70]\n#25 Magento\Framework\ObjectManager\ObjectManager->get() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:206]\n#26 Magento\Framework\ObjectManager\Factory\AbstractFactory->parseArray() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:182]\n#27 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:276]\n#28 Magento\Framework\ObjectManager\Factory\AbstractFactory->getResolvedArgument() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:239]\n#29 Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:34]\n#30 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:59]\n#31 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create() called at [vendor/magento/framework/ObjectManager/ObjectManager.php:70]\n#32 Magento\Framework\ObjectManager\ObjectManager->get() called at [vendor/magento/framework/App/FrontController.php:109]\n#33 Magento\Framework\App\FrontController->__construct() called at [generated/code/Magento/Framework/App/FrontController/Interceptor.php:14]\n#34 Magento\Framework\App\FrontController\Interceptor->__construct() called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:121]\n#35 Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject() called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:66]\n#36 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create() called at [vendor/magento/framework/ObjectManager/ObjectManager.php:70]\n#37 Magento\Framework\ObjectManager\ObjectManager->get() called at [vendor/magento/framework/App/Http.php:115]\n#38 Magento\Framework\App\Http->launch() called at [generated/code/Magento/Framework/App/Http/Interceptor.php:23]\n#39 Magento\Framework\App\Http\Interceptor->launch() called at [vendor/magento/framework/App/Bootstrap.php:264]\n#40

I have Redis installed via Docker on Plesk Control Panel running on CentOS operating system. I restart Redis to get the website back online again, attached is the Redis Container configuration.

Also below is env configuration for Redi

    'cache' => [
        'frontend' => [
            'default' => [
                'backend' => 'Magento\\Framework\\Cache\\Backend\\Redis',
                'backend_options' => [
                    'server' => '127.0.0.1',
                    'database' => '0',
                    'port' => '6379'
                ]
            ],
            'page_cache' => [
                'backend' => 'Magento\\Framework\\Cache\\Backend\\Redis',
                'backend_options' => [
                    'server' => '127.0.0.1',
                    'port' => '6379',
                    'database' => '0',
                    'password' => '',
                    'compress_data' => '1',
                    'force_standalone' => '0',
                    'connect_retries' => '10',
                    'read_timeout' => '30',
                    'automatic_cleaning_factor' => '0',
                    'compress_tags' => '1',
                    'compress_threshold' => '20480',
                    'compression_lib' => 'gzip'
                ]
            ]
        ],
        'allow_parallel_generation' => false,
        'graphql' => [
            'id_salt' => 'xxxxxxxxx'
        ]
    ],
   'session' => [
        'save' => 'redis',
        'redis' => [
            'host' => '127.0.0.1',
            'port' => '6379',
            'password' => '',
            'timeout' => '15',
            'persistent_identifier' => '',
            'database' => '2',
            'compression_threshold' => '2048',
            'compression_library' => 'gzip',
            'log_level' => '1',
            'max_concurrency' => '15',
            'break_after_frontend' => '5',
            'break_after_adminhtml' => '30',
            'first_lifetime' => '600',
            'bot_first_lifetime' => '60',
            'bot_lifetime' => '7200',
            'disable_locking' => '1',
            'min_lifetime' => '60',
            'max_lifetime' => '2592000'
        ]
    ],
    'cache_types' => [
        'config' => 1,
        'layout' => 1,
        'block_html' => 1,
        'collections' => 1,
        'reflection' => 1,
        'db_ddl' => 1,
        'eav' => 1,
        'customer_notification' => 1,
        'config_integration' => 1,
        'config_integration_api' => 1,
        'full_page' => 1,
        'translate' => 1,
        'config_webservice' => 1,
        'compiled_config' => 1,
        'vertex' => 1
    ],

Answer 1

I didn't face this issue yet, but I found some responses to this issue on other sites, they said "Re-installing redis-server seems to have helped".

There is a related issue for Magento 1 on github, you can take a look: https://github.com/colinmollenhour/Cm_Cache_Backend_Redis/issues/155

Btw, the page caching database number should be set to 1 instead of 0 because the default caching was used 0.

Important: If you use Redis for more than one type of caching, the database numbers must be different. It is recommended that you assign the default caching database number to 0, the page caching database number to 1, and the session storage database number to 2.

Reference: https://experienceleague.adobe.com/docs/commerce-operations/configuration-guide/cache/redis/redis-pg-cache.html