Verified in Satellite 6.3.4 Snap 2

Used this loop to send 20 virt-who reports with 25 hypervisors each to the Satellite. 

for i in {1..20}; do docker run --rm -d -e "SATHOST=<my.sat.host>" -e "COUNT=25" jacobcallahan/genvirt; done

This flooded the passenger queue, which is setup with the default 12 workers.

Then i performed a watch for the cert check (Every 2s) and watched for a 503. 

watch "curl -s -u admin:changeme -X GET https://$(hostname -f)/rhsm/consumers/a5832c5a-964d-48ee-9b3a-ece4d79d7fed/certificates/serials"

At no point did a 503 get returned. 

Additionally, grepping the httpd log didn't give any results for the error expected.

-bash-4.2# grep "queue is full" /var/log/httpd/error_log
-bash-4.2#

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:2915