I like the fencing solution. Couldn't such a scheme be implemented over a database instead?
Why I'm thinking more in terms of a database-oriented solution is because there is still the problem of crashing. What happens if the system crashes just before the email is sent? The system somehow needs to remember to restart that task (sending the email) when it comes back up. And this is probably best done through a database anyway.
Why I'm thinking more in terms of a database-oriented solution is because there is still the problem of crashing. What happens if the system crashes just before the email is sent? The system somehow needs to remember to restart that task (sending the email) when it comes back up. And this is probably best done through a database anyway.