ONTAP, both 7-mode and clustered, do not support REST/SOAP APIs directly to the controllers. The API they use is known as ZAPI and is XML/RPC based. The SDKs and documentation are found under the NetApp Manageability SDK on MySupport. The NMSDK has integrations for .NET, Perl, Python, C/C++, Java and more.
The NetApp PowerShell Toolkit is a PowerShell abstraction for ZAPI using the .NET SDK. Each ZAPI has an equivalent cmdlet for it's function. If you are a PowerShell user, then it's a great way to automate against your systems.
API-S can talk directly to clustered ONTAP, however it can't talk directly to 7-mode systems. API-S can talk to Unified Manager though...I'm not sure if a 7-mode system connected to UM would be able to be managed though API-S.
I'll ask and see if I can get an answer for you.
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