#!/bin/bash

WINDOW=Tue:15:00-Tue:15:30

set_window ()
{
    local db_id=$1
    aws rds modify-db-instance \
        --db-instance-identifier $db_id \
        --preferred-maintenance-window $WINDOW
}

get_rds_db_ids ()
{
    aws rds describe-db-instances \
        | jq -r '.DBInstances[].DBInstanceIdentifier'
}

for this_db_id in $(get_rds_db_ids)
do
    set_window $this_db_id
done