Fail to power up virtual machines during provisioning

Problem: When deploying a host to a vCenter computer resource, the process fails with the error “Cannot power up host”.

Expected outcome: Virtual machine is created and powered up, starts network boot.

Foreman and Proxy versions: 3.1.2

The problem was also observed with older versions and since I could not find anything I supose it still persists in recent versions. We will upgrade to 3.3 within the next weeks.

Distribution and version: CentOS 7

Other relevant data:

production.log is revealing an SSL_connect error, presumably for that particular request. Everything works when we uncheck the “Start” checkbox in the Virtual machine tab during host creation and later start the VM manually.

It was no foreman problem. We found that the firewall dropped some pakets. I do not really understand why this only happens in some cases, but this might me specifics of this particular firewall.