As a diploma holder you can join Army, Air Force and Navy in Group X as Soldier, Airman and Sailor respectively.
Group ‘X’ Soldier/Airman/Sailor gets more allowances compared to Group Y candidates. There is approximate 5-6K difference in the payment of Group X and Y soldiers.
You will have the flavors of Both Soldier and Technician.
There are various notifications issued from time to time by Army/Navy/Air Force to recruit diploma holders.
I think after putting some years of service, you may become commissioned officer in Defence which is gazetted officer.
I hope this helps.
In addition to above answered by Vikas I will add following :-
You can also apply in Defence related organization like DRDO (Defence Reasearch & Development Organisation) and MES (Military Engineering Service) as Junior Engineer. I think for Assistant Enginner they need engineering degree. But for Diploma holders I am sure they ask for Diploma in specific trade/stream.