Symfony 4, Doctrine and AWS RDS read replica usage - php

Question

I'm about to embark on using RDS with a master read/write and slave read-only setup.
I've read about the Doctrine MasterSlaveConnection type.
However, there will be some endpoints I create that I would like to use the read-only replica (most of my GET endpoints) and some will need to write data (PUT, PATCH, DELETE endpoints).
I'm also using API Platform.
What is the best way of achieving this in Symfony 4 and Doctrine 2?

Answer 1

What I have done in the past is to just use different connections.
Something like:
doctrine:
dbal:
default_connection: default
connections:
default:
# This is your Master
url: '%env(DATABASE_URL)%'
driver: 'pdo_mysql'
server_version: '5.7'
charset: utf8mb4
slave:
# This would be the slave
url: '%env(DATABASE_SLAVE_URL)%'
driver: 'pdo_mysql'
server_version: '5.7'
charset: utf8mb4
orm:
default_entity_manager: default
entity_managers:
default:
connection: default
mappings:
Main:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/Entity'
prefix: 'App\Entity'
alias: Main
slave:
connection: slave
mappings:
Main:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/Entity'
prefix: 'App\Entity'
alias: Main
https://symfony.com/doc/current/doctrine/multiple_entity_managers.html
Then in your controllers or business logic you can either choose to use the default entity manager:
// Controller
$this->getDoctrine()->getEntityManager();
Or you can get the slave connection:
// Controller
$this->getDoctrine()->getEntityManager('slave');
If you need this to work just on all requests without having to create special actions for everything then your best bet is to decorate the Collection and Item DataProviders for doctrine.
https://symfony.com/doc/current/service_container/service_decoration.html
https://github.com/api-platform/core/blob/master/src/Bridge/Doctrine/Orm/CollectionDataProvider.php
https://github.com/api-platform/core/blob/master/src/Bridge/Doctrine/Orm/ItemDataProvider.php
So basically you need to change what manager is chosen based on the $opperationName something like:
if($opperationName === 'GET'){
$manager = $this->managerRegistry->getManager('slave');
} else {
$manager = $this->managerRegistry->getManager();
}

Answer 2

You actually don't need to setup multiple entity managers, nor is it preferable as handling one entity with multiple entity managers is hard.
Using Doctrine 2.2, you can setup slaves/replicas directly from configuration without needing an extra entity manager:
See the config reference here:
https://www.doctrine-project.org/projects/doctrine-bundle/en/2.2/configuration.html#configuration-overview
Example:
doctrine:
dbal:
default_connection: default
connections:
default:
dbname: '%env(DATABASE_DBNAME)%'
user: '%env(DATABASE_USER)%'
password: '%env(DATABASE_PASSWORD)%'
host: '%env(DATABASE_HOST)%'
driver: 'pdo_mysql'
server_version: '5.7'
charset: utf8mb4
default_table_options:
charset: utf8mb4
collate: utf8mb4_unicode_ci
slaves:
ro_replica:
dbname: '%env(REPLICA_DBNAME)%'
user: '%env(REPLICA_USER)%'
password: '%env(REPLICA_PASSWORD)%'
host: '%env(REPLICA_HOST)%'
charset: utf8mb4

Answer 3

Thank you #Chase for the solution. You have made my day. Although it works for me in 'dev' environment I had a problem when switched to 'prod'. I was getting an error that an Entity can not be found. The solution came from this post - thanks #xabbuh. Basically I had to add default_entity_manager: name_of_default_em to doctrine.yml. Here is the copy of the code:
# config/packages/prod/doctrine.yaml
doctrine:
orm:
default_entity_manager: BOE <- add this line to let know prod about default em
auto_generate_proxy_classes: false
metadata_cache_driver:
type: service
id: doctrine.system_cache_provider
query_cache_driver:
type: service
id: doctrine.system_cache_provider
result_cache_driver:
type: service
id: doctrine.result_cache_provider
# ...