I've seen many posts recently, Experts jumping in and posting, ESXi 5.5 is not supported after September 2018, which is a true statement, but it does not really help the Member posting a question, as to what the issue is today they are experiencing.
also... that is not really a hard and fast rule, Support for ESXi 5.5 CAN be extended if you purchase support.
"In the event you are unable to upgrade before the End of General Support (EOGS) and are active on Support and Subscription, you have the option to purchase extended support in one year increments for up to two years beyond the EOGS date. Visit VMware Extended Support for more information."
"Technical Guidance for vSphere 5.5 is available until September 19, 2020 primarily through the self-help portal"
e.g. all the firmware, security and critical update patches, software will still be available for download, all VMware Kbs, and VMware Communities information will still be available.
What does this mean to you and your organization ?
1. Unless you are covered by a valid support and subscription, and purchased extended support, you will not be able to make a telephone support, or email support, or online support request for vSphere 5.5.
2. If you Support and Subscription has expired - not applicable. You have no support.
3. Is it a Risk to your organisation you have no fourth line support for VMware vSphere 5.5 ?
4. VMware will provide security updates to 5.5, if there is a serious issues which needs addressing.
5. Is your current environment, working and supported, e.g. hardware on the HCL?
To mitigate the risk...
1. Obtain an extended support contract with VMware. (if you are still in Support and Subscription)
2. Obtain a support contract with a third party - VMware Specialist.
3. Use the free resources available at VMware.
4. Use Experts Exchange, there are plenty of Experts with vSphere 5.5 experience! (that hopefully will not shout Upgrade at you!)
Finally, will need purchase of new licenses, if not covered by Support and Subscription
5. Upgrade to 6.0, 6.5 or 6.7 (may require new hardware - check he HCL)
So lots of options, and that may not be UPGRADE!
(and for information we still use ESX 2.5.4 - yes that's correct, not a spelling mistake ESX)
If you would like to discuss this post further please post a question to the VMware Topic area.