If you see the following error in an error log, it is likely that the onapp user has hit its available process limit:
Fatal: can't create Thread
Any OnApp version
To check this matter, please use the following command:
# ps -eLF | grep ^onapp | wc -l
The default maximum value for CentOS6 is 1024. It's 4096 for CentOS7.
This global limit file is located at /etc/security/limits.d/90-nproc.conf. You may also find a per user limit at /etc/security/limits.conf, should you need to increase this value.