Simple scenario: mod_cluster and 4 JBoss nodes are deployed. When a JBoss server fails (JVM is forcibly killed), about 0.5% of sessions result in 503.
These edge scenarios are why people are going to deploy mod_cluster and it should be our priority to provide 100% session correctness. We should target all of these QoS problems for production release since mod_jk handles these cases.
Same question as to
JBPAPP-3463: is there a known workaround we could provide to customers?
503 Service Temporarily Unavailable</title>
<h1>Service Temporarily Unavailable</h1>
<p>The server is temporarily unable to service your
request due to maintenance downtime or capacity
problems. Please try again later.</p>
<address>Apache/2.2.10 (Red Hat) Server at perf08 Port 8888</address>
perf01-perf04 = JBoss nodes
perf08 = mod_cluster + load driver node