To do SSH, enable the option provided in ESXi Console
Remote Access to ESXi Shell Using SSH
If Secure Shell is enabled for the ESXi Shell, you can run shell commands by using a Secure Shell client such as SSH or PuTTY.
Enabling SSH for the ESXi Shell
By default, you cannot access the ESXi Shell using a Secure Shell client. You can enable SSH access from the direct console.
To enable SSH access in the direct console
1
| At the direct console of the ESXi host, press F2 and provide credentials when prompted. |
2
| Scroll to Troubleshooting Options, and press Enter. |
3
| Select Enable SSH and press Enter once. |
On the left, Enable SSH changes to Disable SSH. On the right, SSH is Disabled changes to SSH is Enabled.
4
| Press Esc until you return to the main direct console screen. |
When 5.1 to 5.5 vCenter Server upgrads, its expected to push new agent of HA in to ESXi to work HA seemlessly with new upgraded vCenter. Looks its failed here.
Try installing new agent by doing following steps
- Login to ESXi
- run command esxcli software install https://<vCenter Server IP address>/vSphere-HA-depot/index.xml
- It install the agent named vmware-fdm, make sure the agent installation completed by list down the agent by running
#esxcli software vib list |grep -ivmware-fdm
- follow the above step on second esxi server
- Reconfigure HA
Hope it helps