503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http20NamedPipeServiceSpecE:0x4bf02038] _serverNamespace = /mob _isRedirect = false _pipeName =/var/run/vmware/proxy-mob)
This was the first time I had noticed this as I normally use the vSphere MOB for debugging purposes or exploring the vSphere API. The vSphere MOB is also a quick an handy way to unregister vSphere Plugins when connecting to vCenter Server.
I did some further investigation and it turns out that in vSphere 6.0, the vSphere MOB will be disabled by default on an ESXi 6.0 host. The reason for this is to provide security hardening out of the box for ESXi versus having an administrator harden after the fact. If you are familiar with the vSphere Security Hardening Guides, you will recall one of the guidelines is to disable the vSphere MOB on an ESXi host and with vSphere 6.0, this is now done automatically for you. This information will also be documented as part of the vSphere 6.0 documentation when it GAs.
If you still need to access the vSphere MOB on an ESXi how, this of course can be re-enabled from the default. There is also a new ESXi Advanced Setting called Config.HostAgent.plugins.solo.enableMob which easily controls whether the vSphere MOB is enabled or disabled as seen in the screenshot below.