MySQLSQLAlchemyFailover.py

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"""SQLAlchemy + AWS Advanced Python Wrapper: failover on Aurora MySQL."""

from sqlalchemy import create_engine, text
from sqlalchemy.exc import OperationalError

from aws_advanced_python_wrapper import release_resources
from aws_advanced_python_wrapper.mysql_connector import connect

CLUSTER_ENDPOINT = "database.cluster-xyz.us-east-1.rds.amazonaws.com"
DB_NAME = "mysql"
USER = "john"
PASSWORD = "pwd"


def build_engine():
    return create_engine(
        "mysql+aws_wrapper_mysqlconnector://",
        creator=lambda: connect(
            f"host={CLUSTER_ENDPOINT} database={DB_NAME} user={USER} password={PASSWORD}",
            wrapper_dialect="aurora-mysql",
            plugins="failover",
            use_pure=True,
        ),
    )


def run_workload(engine, iterations: int = 20) -> None:
    for i in range(iterations):
        try:
            with engine.connect() as conn:
                row = conn.execute(text("SELECT @@aurora_server_id")).one()
                print(f"iter {i}: connected to instance {row[0]}")
        except OperationalError as exc:
            print(f"iter {i}: operational error ({type(exc.orig).__name__}); retrying")


def main() -> None:
    engine = build_engine()
    try:
        run_workload(engine)
    finally:
        engine.dispose()
        release_resources()


if __name__ == "__main__":
    main()