[aio] aurora_connection_tracker closes its own connection on the first statement of every cluster-endpoint connection

[samantha-earthmover]

Describe the bug

With the async wrapper (aws_advanced_python_wrapper.aio, via the postgresql+aws_wrapper_psycopg SQLAlchemy dialect) and the default plugin chain, every new connection to an Aurora PostgreSQL cluster writer endpoint fails on its first statement with FailoverSuccessError. The retries also open several connections per attempt (the failover's writer connection plus topology probes), which push a huge spike in connection count.

Expected Behavior

A connection made through the cluster writer endpoint with the default plugins should run its first statement normally, as it does with wrapper_plugins=failover,host_monitoring_v2 (the chain used in docs/examples/PGSQLAlchemyAsyncFailover.py).

What plugins are used? What other connection properties were set?

Default chain (wrapper_plugins not set, so initial_connection,aurora_connection_tracker,failover_v2,host_monitoring_v2), wrapper_dialect=aurora-pg. Also reproduced with wrapper_plugins=aurora_connection_tracker alone. Does not reproduce with wrapper_plugins=failover,host_monitoring_v2 or failover_v2 alone.

Current Behavior

Every connection, on its first statement:

aws_advanced_python_wrapper.aio.aurora_connection_tracker: [OpenedConnectionTracker] Invalidating opened connections to host: <name>.cluster-<id>.us-east-1.rds.amazonaws.com:5432/
aws_advanced_python_wrapper.aio.aurora_connection_tracker: [OpenedConnectionTracker] Opened Connections Tracked:
aws_advanced_python_wrapper.aio.aurora_connection_tracker: [AsyncAuroraConnectionTrackerPlugin] failover handler: pre=<name>.cluster-<id>.us-east-1.rds.amazonaws.com:5432/ post=tf-2026061217...chnc4uhow0rs.us-east-1.rds.amazonaws.com:5432/ pinned=tf-2026061217...chnc4uhow0rs.us-east-1.rds.amazonaws.com:5432/
aws_advanced_python_wrapper.aio.aurora_connection_tracker: [OpenedConnectionTracker] Invalidating opened connections to host: <name>.cluster-<id>.us-east-1.rds.amazonaws.com:5432/
iter 0: operational error (FailoverSuccessError)

Reproduction Steps

import asyncio, logging, os, sys
from sqlalchemy import text
from sqlalchemy.exc import OperationalError
from sqlalchemy.ext.asyncio import create_async_engine
from aws_advanced_python_wrapper.aio import release_resources_async

logging.basicConfig(level=logging.WARNING, stream=sys.stdout, format="%(name)s: %(message)s")
logging.getLogger("aws_advanced_python_wrapper.aio.aurora_connection_tracker").setLevel(logging.DEBUG)

CLUSTER_ENDPOINT, DB_NAME, USER, PASSWORD = (os.environ[k] for k in ("PGHOST", "PGDATABASE", "PGUSER", "PGPASSWORD"))
PLUGINS = "" if sys.argv[1] == "default" else "&wrapper_plugins=failover,host_monitoring_v2"

async def main():
    engine = create_async_engine(
        f"postgresql+aws_wrapper_psycopg://{USER}:{PASSWORD}@{CLUSTER_ENDPOINT}:5432/{DB_NAME}"
        f"?wrapper_dialect=aurora-pg{PLUGINS}")
    try:
        for i in range(3):
            try:
                async with engine.connect() as conn:
                    row = await conn.execute(text("SELECT pg_catalog.aurora_db_instance_identifier()"))
                    print(f"iter {i}: connected to instance {row.scalar_one()}")
            except OperationalError as exc:
                print(f"iter {i}: operational error ({type(exc.orig).__name__})")
    finally:
        await engine.dispose()
        await release_resources_async()

asyncio.run(main())

Possible Solution

Claude output

In aws_advanced_python_wrapper/aio/aurora_connection_tracker.py, _pin_current_writer first pins the writer from topology, which is the instance endpoint. Its stale-topology guard then calls get_host_role(conn), gets WRITER, and replaces the pin with plugin_service.current_host_info, which is the URL host, i.e. the cluster endpoint. _same_host compares host strings, so the cluster endpoint never equals the instance endpoint. On the first execute, _invalidate_writer_change compares the cluster-endpoint pin with the instance-endpoint topology writer, reports a writer change, and invalidate_all closes every connection keyed under the cluster endpoint, which after _fill_instance_alias includes the connection about to execute. The sync tracker does not pin at connect time and only compares instance against instance, so it is unaffected.

Additional Information/Context

No response

The AWS Advanced Python Wrapper version used

3.1.0

python version used

3.14.7

Operating System and version

Debian GNU/Linux 12 (bookworm), aarch64, python:3.14-slim image

[karenc-bq]

Hi @samantha-earthmover, thank you for reporting the issue, we will take a look and keep you updated on the progress!