Patch apply in DMZ environment

Hi

Need suggestion on applying patch on DMZ Node.

The environment is as following

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3 DB Nodes
2 Application Nodes (internal Application)
2 Application Nodes  (External Application) -DMZ

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MERP and NERP are external nodes ,MPROD and NPROD are internal nodes

MERP  ConcMgr FORMS Web  Admin No
NERP  ConcMgr FORMS Web  Admin No
NPROD ConcMgr FORMS Web  Admin No

MPROD ConcMgr FORMS Web  Admin No

Both external and internal nodes are having same database (sharing same db)

Even though external are having ConcMgr Forms Web Admin but it is configured for accessing self service only,

no oracle forms also (trusted responsibility is set). Also no FND process are runing on it.(ps -ef|grep FND).