Mirrord DB Branching Skill

Purpose

Generate and validate mirrord.json configurations for database branching:

Generate valid db_branches configs from natural language descriptions
Explain copy modes, IAM authentication, and branch management
Validate user-provided configs against schema requirements
Troubleshoot common DB branching issues

References

For complete documentation, see:

Critical First Steps

Step 0: Load References Read the reference files from this skill's references/ directory:

references/db-branches-schema.json - Authoritative JSON Schema for db_branches configuration
references/troubleshooting.md - Common issues and solutions

The schema is derived from the official mirrord schema at: https://raw.githubusercontent.com/metalbear-co/mirrord/main/mirrord-schema.json

If using absolute paths, search for the schema using patterns like **/mirrord-db-branching/references/*.

Step 1: Verify Prerequisites

For MySQL:

Operator 3.129.0+, mirrord CLI 3.160.0+, Helm chart 1.37.0+
Helm chart must have operator.mysqlBranching: true

For PostgreSQL:

Operator 3.131.0+, mirrord CLI 3.175.0+, Helm chart 1.40.2+
Helm chart must have operator.pgBranching: true

Step 2: Identify Connection Environment Variable The application must use an environment variable for the database connection string. mirrord will override this variable with the branch connection URL.

Step 3: Validate Configuration After generating any config, ALWAYS run:

mirrord verify-config /path/to/config.json

Configuration Structure

Basic DB Branch Configuration

{
  "db_branches": [
    {
      "id": "unique-branch-identifier",
      "type": "mysql",
      "version": "8.0",
      "name": "database-name",
      "ttl_secs": 60,
      "creation_timeout_secs": 20,
      "connection": {
        "url": {
          "type": "env",
          "variable": "DB_CONNECTION_URL"
        }
      },
      "copy": {
        "mode": "empty"
      }
    }
  ]
}

Supported Database Types

Type	Value	Notes
MySQL	`"mysql"`	Requires operator.mysqlBranching: true
PostgreSQL	`"pg"`	Requires operator.pgBranching: true, supports IAM auth
MongoDB	`"mongodb"`	Uses collections instead of tables
Redis	`"redis"`	Can run locally or remotely

Configuration Fields (MySQL, PostgreSQL, MongoDB)

Field	Required	Description
`type`	Yes	Database engine: `"mysql"`, `"pg"`, or `"mongodb"`
`connection`	Yes	Connection source configuration
`connection.url.type`	Yes	Must be `"env"` or `"env_from"`
`connection.url.variable`	Yes	Environment variable storing the connection string
`id`	No	Branch identifier for reuse; same ID reconnects to existing branch
`name`	No	Database name when not accessible from connection
`version`	No	Engine version (e.g., `"8.0"` for MySQL, `"16"` for PostgreSQL)
`ttl_secs`	No	Branch lifetime in seconds (max 900 / 15 minutes, default 300 / 5 minutes)
`creation_timeout_secs`	No	Setup timeout (default 60 seconds)
`copy.mode`	No	Cloning strategy (default `"empty"`)
`iam_auth`	No	Cloud IAM authentication (PostgreSQL only)

Configuration Fields (Redis)

Field	Required	Description
`type`	Yes	Must be `"redis"`
`location`	No	`"local"` or `"remote"` (default: `"remote"`)
`connection`	No	Redis connection config (URL or host/port/password)
`id`	No	Branch identifier for reuse
`local`	No	Local Redis runtime config (when location is `"local"`)

Copy Modes

Empty Database (Default)

Creates an empty database with no schema or data. Use when your application handles migrations on startup.

{
  "copy": {
    "mode": "empty"
  }
}

Schema Only

Replicates table structures without data. Good for testing schema modifications.

{
  "copy": {
    "mode": "schema"
  }
}

Complete Database

Copies schema and all data. Use only for small databases as this increases creation time significantly.

{
  "copy": {
    "mode": "all"
  }
}

Filtered Data Clone (MySQL/PostgreSQL)

Copy schema plus filtered rows from specific tables. Cannot be combined with "mode": "all".

{
  "copy": {
    "mode": "schema",
    "tables": {
      "users": {"filter": "name = 'alice' OR name = 'bob'"},
      "orders": {"filter": "created_at > 1759948761"}
    }
  }
}

MongoDB Copy Modes

MongoDB uses collections instead of tables:

{
  "copy": {
    "mode": "all",
    "collections": {
      "users": {"filter": "{\"name\": {\"$in\": [\"alice\", \"bob\"]}}"},
      "orders": {"filter": "{\"created_at\": {\"$gt\": 1759948761}}"}
    }
  }
}

Redis Configuration

Redis branches can run locally or use the remote instance.

Local Redis Branch

{
  "db_branches": [
    {
      "type": "redis",
      "location": "local",
      "connection": {
        "url": {
          "type": "env",
          "variable": "REDIS_URL"
        }
      },
      "local": {
        "runtime": "container",
        "container_runtime": "docker",
        "port": 6379,
        "version": "7-alpine"
      }
    }
  ]
}

Redis with Separated Connection

{
  "db_branches": [
    {
      "type": "redis",
      "location": "local",
      "connection": {
        "host": {
          "type": "env",
          "variable": "REDIS_HOST"
        },
        "port": 6379,
        "password": {
          "type": "env",
          "variable": "REDIS_PASSWORD"
        }
      }
    }
  ]
}

IAM Authentication

AWS RDS

Uses credentials from the target pod's environment:

{
  "iam_auth": {
    "type": "aws_rds"
  }
}

Default variables checked: AWS_REGION, AWS_DEFAULT_REGION, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_SESSION_TOKEN

GCP Cloud SQL

Important: Requires TLS - ensure connection URL includes sslmode=require

{
  "iam_auth": {
    "type": "gcp_cloud_sql"
  }
}

Uses GOOGLE_APPLICATION_CREDENTIALS by default. Can override with:

credentials_json - Inline JSON credentials
credentials_path - Custom file path

Branch Management Commands

View Branch Status

mirrord db-branches [-n namespace] status [branch-names...]
mirrord db-branches --all-namespaces status

Destroy Branches

mirrord db-branches [-n namespace] destroy branch-name
mirrord db-branches [-n namespace] destroy --all
mirrord db-branches --all-namespaces destroy --all

Common Pitfalls

Issue	Solution
Connection timeouts	Branch databases disable SSL by default; verify client isn't forcing SSL
GCP Cloud SQL fails	Ensure connection URL includes `sslmode=require`
Branch creation slow	Using `"mode": "all"` on large database; switch to `"schema"` or `"empty"`
Branch not reused	Ensure `id` field is set and matches; check TTL hasn't expired
Wrong database connected	Verify `connection.url.variable` matches your app's actual env var

What to Ask (only if critical)

If the request is under-specified, ask for ONE detail:

Database type (MySQL or PostgreSQL)
Environment variable name for connection string
Copy mode preference (empty, schema, or all)
Whether IAM authentication is needed (AWS RDS or GCP Cloud SQL)

Otherwise, provide safe defaults and note assumptions.

Example Scenarios

MySQL branch with schema copy

User: "I want to test migrations on my MySQL database without affecting production"

{
  "db_branches": [
    {
      "id": "migration-test",
      "type": "mysql",
      "version": "8.0",
      "name": "myapp_production",
      "ttl_secs": 300,
      "connection": {
        "url": {
          "type": "env",
          "variable": "DATABASE_URL"
        }
      },
      "copy": {
        "mode": "schema"
      }
    }
  ]
}

PostgreSQL with AWS RDS IAM

User: "Set up a Postgres branch using AWS IAM authentication"

{
  "db_branches": [
    {
      "type": "pg",
      "version": "16",
      "name": "app_db",
      "connection": {
        "url": {
          "type": "env",
          "variable": "PG_CONNECTION_STRING"
        }
      },
      "copy": {
        "mode": "empty"
      },
      "iam_auth": {
        "type": "aws_rds"
      }
    }
  ]
}

Filtered data for testing

User: "I need a branch with only test users from the users table"

{
  "db_branches": [
    {
      "id": "test-data-branch",
      "type": "pg",
      "version": "15",
      "name": "production_db",
      "connection": {
        "url": {
          "type": "env",
          "variable": "DATABASE_URL"
        }
      },
      "copy": {
        "mode": "schema",
        "tables": {
          "users": {"filter": "email LIKE '%@test.com'"}
        }
      }
    }
  ]
}

MongoDB branch

User: "Set up a MongoDB branch that copies specific users"

{
  "db_branches": [
    {
      "type": "mongodb",
      "version": "7.0",
      "name": "app_database",
      "connection": {
        "url": {
          "type": "env",
          "variable": "MONGODB_URI"
        }
      },
      "copy": {
        "mode": "all",
        "collections": {
          "users": {"filter": "{\"role\": \"admin\"}"}
        }
      }
    }
  ]
}

Local Redis for development

User: "I want a local Redis instance for my development session"

{
  "db_branches": [
    {
      "type": "redis",
      "id": "dev-redis",
      "location": "local",
      "connection": {
        "url": {
          "type": "env",
          "variable": "REDIS_URL"
        }
      },
      "local": {
        "runtime": "container",
        "container_runtime": "docker",
        "version": "7-alpine"
      }
    }
  ]
}

Quality Requirements

Valid JSON: Always parseable, no comments or trailing commas
Minimal configs: Only include fields the user actually needs
Correct types: Use proper database types ("mysql" or "pg")
Safe defaults: Default to "empty" copy mode to avoid long creation times
Actionable feedback: Explain what each field does when relevant