Migrate (On only one server out of n)

[iBotPeaches]

Hitting an interesting issue, where we took our AWS setup from 1/at-a-time to half-at-a-time. Mainly because many servers, a more popular platform that deploying one at a time was taking forever.

Now if 4 servers attempt to release at same point - chances are they will migrate at same time and fail. I tried random sleeps in scripts to prevent same-time (it was hacky as hell)

I dug into AWS and it doesn't support a one first, then half later.

So to the idea. Wouldn't it be cool to have like php artisan migrate --on-one-server or something? It would use the same locking behavior that cron locks do in order to isolate to one server. So we can have a fast deploy with only 1 server migrating.

[mikeydevelops]

I assume you are sharing one database server? Do you also share one caching server i.e Redis,Memcached,Dynamodb?

First thing you need is to define a cache store in config/cache.php. I will use a database driver. Decided to name it sync.

// config/cache.php

// ...

/*
|----------------------------------------------------------------------
|  Migration Mutex Cache Store
|----------------------------------------------------------------------
|
| The name of the cache store where the migration mutex will
| be aquired when migrating the database.
|
*/
'migration_mutex_store' => env('CACHE_MIGRATION_MUTEX_STORE'),

'stores' => [
    // ...

    'sync' => [
        'driver' => 'database',
        'table' => 'cache',
        'connection' => null, // probably it would be best if you had different connection for private use, instead of the one you use to serve you clients, you know - just in case.
    ],

    // ...
],

Then we can create a migrate command which will extend the original implementation but first it will try to acquire lock before migrating:

// app/Commands/MigrateCommand.php

<?php

namespace App\Console\Commands;

use Illuminate\Contracts\Events\Dispatcher;
use Illuminate\Database\Console\Migrations\MigrateCommand as IlluminateMigrateCommand;
use Illuminate\Database\Migrations\Migrator;

class MigrateCommand extends IlluminateMigrateCommand
{

    /**
     * Create a new migration command instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->signature .= '{--mutex : Migrate only when no mutex is present.}
                             {--mutex-store= : The cache store to be used to acquire the mutex.}';

        parent::__construct(app('migrator'), app(Dispatcher::class));
    }

    /**
     * Execute the console command.
     *
     * @return int
     */
    public function handle()
    {
        $lock = $this->acquireLock();

        if ($lock && ! $lock->get()) {
            $store = $this->getMutexStore();

            $this->error("Unable to aquire cache lock [$store] for migrating, aborting.");

            return 1;
        }

        try {
            $exitCode = parent::handle();
        } finally {
            if ($lock) {
                $lock->release();
            }
        }

        return $exitCode;
    }

    /**
     * Aquire the mutex lock.
     *
     * @return \Illuminate\Cache\Lock|false
     */
    public function acquireLock()
    {
        if (! $this->option('mutex')) {
            return false;
        }

        /** @var \Illuminate\Contracts\Cache\LockProvider $store */
        $store = $this->laravel->make('cache')->store($this->getMutexStore());

        return $store->lock('migrating');
    }

    /**
     * Get the cache store name where the mutex will be stored.
     *
     * @return string
     */
    public function getMutexStore()
    {
        return $this->option('mutex-store')
            ?? $this->laravel->make('config')->get('cache.migration_mutex_store')
            ?? $this->laravel->make('config')->get('cache.default');
    }
}

Our command should now be registered automatically, if that is not the case go in app/Console/Kernel.php and append Commands\MigrateCommand::class to the $commands array.

Now when you want to migrate once you run php artisan migrate --mutex --mutex-store=sync.

Just so you know, I did not test this on multiple servers but instead with 4 terminals running the same command in a while loop. And it is working as expected.

[iBotPeaches]

Thanks! Will dive in after a Laravel upgrade and look into implementing.

[mikeydevelops]

Made a small change to take into account any unexpected exceptions and added try-finally block to make sure the lock is released when the exceptions occur.

[olivernybroe]

Before moving on this, has anyone submitted something like this to laravel/framework or moved into a package already?

[chrillep]

same issue for initcontainers in kubernetes

laravel/ideas#1645
could be a solution

[chrillep]

or #38887
https://github.com/erjanmx/laravel-migrate-check