What would you do if you found that a PostgreSQL container unexpectedly stopped or was reset?

If a PostgreSQL container unexpectedly stops or is reset, I would take the following steps:

1. Check container logs: using docker logs <container_id> to determine the cause of the stop — errors, resource shortages, configuration failures.

2. Check host status: ensure that the server has sufficient resources (CPU, memory, disk) and no network issues.

3. Check data: ensure that the database data is saved in a volume or on the host to prevent data loss upon restart.

4. Restart the container: try to start the container again using docker start or docker run with the correct parameters.

5. Monitoring and alerts: set up a monitoring system (e.g., Prometheus + Grafana) and alerts to quickly respond to such incidents in the future.

6. Root cause analysis and prevention: if the cause is a configuration error or bug, fix it; if resource limitations are the issue, increase resources or optimize the load.

Thus, it is important to quickly identify the cause of the stop, preserve data, and restore service operation.