MariaDB read-only replication

You can improve the performance of read-heavy applications by defining read-only replicas of your MariaDB database and then connecting your applications to those replicas.

Examples of read-heavy applications include:

• Listing pages or dashboards
• Reporting or analytics jobs
• Background jobs that frequently query data

Read-only vs. external replicas

Read-only replicas are used primarily to improve application performance by distributing database read requests from read-heavy applications.

Other common use cases for read-only replicas include:

• Cross-region backup: Replicating data to different geographical regions
• Data warehousing: Extracting data from production to analytics projects

External replicas reside on remote servers and have different use cases, including disaster recovery.

Replica scope and sharing services

MariaDB services (which provide access to databases and replicas) defined in a project cannot be accessed by or shared with applications in other projects.

1. Configure the primary and replica services

The following code fragment defines two MariaDB services: a primary and a replica. You can use this fragment as a template by copying it into your services.yaml or application.yaml file.

Be sure to:

• Replace <VERSION> with the supported MariaDB version that you need. Use the same version number for the primary and replica services.
• Important: Use replicator as the endpoint name when you define the replica service. This is a special endpoint name that the replica service uses to connect to the database.

services:
  db:
    type: mariadb:<VERSION>
    configuration:
      schemas:
        - main
      endpoints:
        main:
          default_schema: main
          privileges:
              main: admin
          replicator:
            privileges:
              main: replication

  db-replica1:
    type: mariadb-replica:<VERSION>
    configuration:
      schemas:
        - main
      endpoints:
        main:
          default_schema: main
          privileges:
            main: admin
      relationships:
      primary: db:replicator # Do not change the name `primary`. The service expects to receive this name.

  db-replica2:
    type: mariadb-replica:<VERSION>
    configuration:
      schemas:
        - main
      endpoints:
        main:
          default_schema: main
          privileges:
            main: admin
      relationships:
      primary: db:replicator # Do not change the name `primary`. The service expects to receive this name.

How it works

Using the sample code fragment above:

1. The primary service (db) defines an additional replicator endpoint, granting the replication privilege. This enables a replica to connect and continuously replicate data from the primary database.

   replicator:
     privileges:
       main: replication

2. The replica services (db-replica1 and db-relica2) use the mariadb-replica image type and connect back to the primary database service through the primary relationship. This establishes a replication link from db (the source) to db-replica (the target).

   relationships:
     primary: db:replicator

The db-replica1 and db-replica2 replica services continuously stream data from the primary endpoint, maintaining a read-only copy of the primary database content. Write operations are not permitted on the replicas.

2. Define the relationship between the application and the replicas

Even if your application won’t access the replication endpoint, you must expose the endpoint to an application as a relationship so that you can connect to it over SSH.

Define a new relationship in your application container, as shown below:

name: myapp

[...]

# Relationships enable an app container's access to a service.
relationships:
  # More information: https://fixed.docs.upsun.com/anchors/fixed/app/reference/relationships/
  database:
    service: db
    endpoint: main
  database-readonly:
    service: db-replica

If your application’s performance is still not what you expect, you can configure additional replicas as described above.