Magento2: Varnish health check failing due to presence of id_prefix in env.php

[mikelevy300]

Preconditions (*)

1. Magento 2.3.1
2. PHP 7.2.16
3. Centos 7.6.1810
4. Apache 2.4.6
5. MySQL 5.7.23

Steps to reproduce (*)

1. Install a fresh copy of Magento 2.3.1
2. Configure the frontend cache to use Redis
3. Export varnish.vcl from admin panel and configure Varnish to sit in front of Apache per instructions at https://devdocs.magento.com/guides/v2.3/config-guide/varnish/config-varnish-configure.html
4. Try to load the site

Expected result (*)

1. Pages load, can browse the site, access the admin panel, etc

Actual result (*)

1. A 503 Backend fetch failed is returned by Varnish

Additional information

The root of the issue has to do with the fix for GitHub-15828 and how pub/health_check.php works. In the release notes for 2.3.1 it says

Magento now sets the id_prefix option on prefix cache keys for the cache frontend during installation. If this option is not set, Magento uses the first 12 bits of the md5 hash of the absolute path to the Magento app/etc directory. But if this value is not exactly the same on all web servers, cache invalidation will not work.

After doing a fresh install, here's what the cache part of my env.php looks like

 'cache' => [
        'frontend' => [
            'default' => [
                'backend' => 'Cm_Cache_Backend_Redis',
                'backend_options' => [
                        'server' => '127.0.0.1',
                        'port' => '6379',
                        'persistent' => '',
                        'database' => '0',
                        'password' => '',
                        'force_standalone' => '0',
                        'connect_retries' => '1',
                        'read_timeout' => '10',
                        'automatic_cleaning_factor' => '0',
                        'compress_data' => '1',
                        'compress_tags' => '1',
                        'compress_threshold' => '20480',
                        'compression_lib' => 'gzip',
                        'use_lua' => '0',
                ],
                'id_prefix' => '40d_'
            ],
            'page_cache' => [
                'id_prefix' => '40d_'
            ]
        ]
    ],

Then in health_check.php the relevant section that checks that the cache configuration is valid reads

$cacheConfigs = $deploymentConfig->get(ConfigOptionsListConstants::KEY_CACHE_FRONTEND);
if ($cacheConfigs) {
    foreach ($cacheConfigs as $cacheConfig) {
        if (!isset($cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND]) ||
            !isset($cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND_OPTIONS])) {
            http_response_code(500);
            $logger->error("Cache configuration is invalid");
            exit(1);
        }
        $cacheBackendClass = $cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND];
        try {
            /** @var \Zend_Cache_Backend_Interface $backend */
            $backend = new $cacheBackendClass($cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND_OPTIONS]);
            $backend->test('test_cache_id');
        } catch (\Exception $e) {
            http_response_code(500);
            $logger->error("Cache storage is not accessible");
            exit(1);
        }
    }
}

The code above is grabbing the 'default' array item and the 'page_cache' array item into $cacheConfigs and when it iterates over the 'page_cache' array item, it finds that it contains neither the 'backend' element nor the 'backend_options' element and throws a 500, which in turn causes the healthcheck in Varnish to fail and Varnish to think the backend is down when it's not.

Along with all that, if you tried to use varnish without Redis as the frontend cache, the healthcheck would also fail in the same section because the 'default' element now would not have either the 'backend' element or the 'backend_options' element.

[m2-assistant[bot]]

Hi @mikelevy300. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• [ ] Summary of the issue
• [ ] Information on your environment
• [ ] Steps to reproduce
• [ ] Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento-engcom-team give me 2.3-develop instance - upcoming 2.3.x release

For more details, please, review the Magento Contributor Assistant documentation.

@mikelevy300 do you confirm that you was able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• [ ] yes
• [ ] no

[iamlolz]

I am also experiencing this issue with a fresh install using
Magento 2.3.1
PHP 7.2.16
Centos 7.6.1810
Nginx 1.15.2
MySQL 5.6.43
Varnish 5.2.1
Redis 3.2.12

[m2-assistant[bot]]

Hi @engcom-backlog-nazar. Thank you for working on this issue.
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[magento-engcom-team]

:white_check_mark: Confirmed by @engcom-backlog-nazar
Thank you for verifying the issue. Based on the provided information internal tickets MAGETWO-99102, MAGETWO-99103 were created

Issue Available: @engcom-backlog-nazar, _You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself._

[m2-assistant[bot]]

Hi @Nazar65. Thank you for working on this issue.
Looks like this issue is already verified and confirmed. But if you want to validate it one more time, please, go though the following instruction:

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• [ ] 2. Verify that the issue is reproducible on 2.3-develop branch

  Details

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• [ ] 4. If the issue is not relevant or is not reproducible any more, feel free to close it.

[craigcarnell]

@Nazar65 When is this going to be fixed? It is affecting our live site.

[Nazar65]

@craigcarnell i've made a fix and this fix works, but as @orlangur says we need to cover flow with empty redis config. but you may apply this in health_check.php and have no issue with this
after line 45

        if (count($cacheConfig) === 1 && isset($cacheConfig['id_prefix'])) {
           continue;
}

[DirkBlade]

I have same problem without redis frontend when adding varnish http-cache-hosts from the command line sometime after upgrade to 2.3.1

The command (IPs redacted):
bin/magento setup:config:set --http-cache-hosts=##.###.##.###:####

Resulted in the addition of the cache key to env.php (as well as the expected http_cache_hosts) and immediately health_check.php started 500ing.
...

    'http_cache_hosts' => [
        [
            'host' => '##.###.##.###',
            'port' => '####'
        ]
    ],
    'cache' => [
        'frontend' => [
            'default' => [
                'id_prefix' => '40d_'
            ],
            'page_cache' => [
                'id_prefix' => '40d_'
            ]
        ]
    ]
...

Couldn't we simply ignore empty $cacheBackendClass and assume any class won't instantiate and ->test() successfully within the try block if classname or CONFIG_PATH_BACKEND_OPTIONS are invalid?
e.g.
$cacheConfigs = $deploymentConfig->get(ConfigOptionsListConstants::KEY_CACHE_FRONTEND);
if ($cacheConfigs) {
 foreach ($cacheConfigs as $cacheConfig) {
  if (!empty($cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND])) {
   $cacheBackendClass = $cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND];
   try {
    /** @var \Zend_Cache_Backend_Interface $backend */
    $backend = new $cacheBackendClass($cacheConfig[ConfigOptionsListConstants::CONFIG_PATH_BACKEND_OPTIONS]);
    $backend->test('test_cache_id');
   } catch (\Exception $e) {
    http_response_code(500);
    $logger->error("Cache storage is not accessible");
    exit(1);
  }
  }
 }
}

Just want the bug fixed but I do wonder if Zend_Cache_Backend_Interface should get id_prefix?

Also should we be checking caching_application and http-cache-hosts, potentially validating the connecting IP address?

[magento-engcom-team]

Hi @mikelevy300, @Nazar65.

Thank you for your report and collaboration!

The issue was fixed by Magento team.

The fix will be available with the upcoming 2.3.3 release.