I have set up composer-rest-server successfully using this link on IBM cloud. I have written custom logic code in GoLang for getting chain code. I don't know how will proceed for next setup for getting chain code. Could you help me by showing me which way I have to proceed?
Chaincode for Hyperledger Composer is written in Javascript not GoLang. (Though Hyperledger Fabric supports both GoLang and Javascript with V1.1).
If you wish to proceed with Composer and Javascript, you could start with the Developer Tutorial, then follow this document for information on Developing Applications.
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There is a Fabric Tutorial "First Application" that uses go for the chaincode.
With regard to IBM cloud, it is possible to use Composer Business Networks, or write direct chaincode for the Fabric with IBM Cloud Starter Plan, and there are examples to "auto" deploy.