TCP With Firewall
Understand how firewalls affect persistent TCP connections in distributed systems. Explore the reasons behind connection drops despite TCP allowing long-lived sockets. Learn how firewalls use access control lists to manage connections and why they terminate idle connections, causing application stability challenges. Gain insights into diagnosing and mitigating firewall-related stability antipatterns.
What happened the next day
Sure enough, the pattern repeated itself the next morning. Application servers locked up tight as a drum, with the threads inside the JDBC driver.
Absence of traffic
This time, we were able to look at traffic on the databases’ network, but found nothing at all. The utter absence of traffic on that side of the firewall was like Sherlock Holmes’ dog that didn’t bark in the night—the absence of activity was the biggest clue.
Decomposition of the server
We had a hypothesis. Quick decompilation of the application server’s resource pool class confirmed that our hypothesis was plausible.
How long can a connection persist?
We said before that socket connections are an abstraction; they ...