Hyperledger Composer nodes

Question

I am new to Hyperledger and would like to build a proof-of-concept using Hyperledger Composer. I know Composer is a toolset to build Blockchain-Applications, which can be deployed on Hyperledger Fabric. Still, I don't really understand the structure of Hyperledger Composer, so I have the following questions:

• Am I building an actual Blockchain using Hyperledger Composer or is it just simulated?
• Who are the peers or nodes using Composer? Are there several or just one and how can I choose them?
• I know Fabric uses several consensus mechanisms. As I can't define them using Composer what is the used consensus mechanism? Am I defining them using the Access Control?

I am sorry if the questions may seem stupid but I am new in this field and can't find the answers online.

Answer 1

I would recommend following the tutorials for a hyperledger fabric's first network as Composer is very restrictive when it comes to customizing the network structure (ie adding more nodes and/or organisations)

Composer is good for writing up quick smart contracts and connecting it to an app for a demo as it is easy to test and generates an API for the chain code.

When running a Composer locally, it will run the 2 organisation 2 peer network outlined in fabric first network tutorial. It will then install the chain code you have written and generate an API for it.

As for your last point about the consensus mechanism I'm not to sure.

Answer 2

• You are basically defining and developing a blockchain network with composer. The bna file that is created with composer can be deployed locally or in a production environment (atleast that's the plan, not sure if composer is actually there yet because there's still not a v1 for composer)
• When you deploy a bna file locally, you're deploying your blockchain network onto docker containers in your local machine. You can run the ./startFabric.sh script and then do a docker ps this will list your docker containers and what their purpose is (e.g peer, orderer etc). There are no peers or orderers in composer itself. That is all on fabric.
• Fabric uses the ordering service to maintain consensus. The ordering service is responsible for checking access control rules, cryptographic material, identities, consensus etc. If your environment has only 1 orderer then there isn't much to worry about consensus. But if you have more than 1 orderer then there are going to be issues. To solve these issues, and mantain consensus, an apache kafka implementation is used on the ordering service which basically distributes the requests across different orderers.

Answer 3

No, you're not building a blockchain. The blockchain is created using Fabric. You're just developing and deploying your chaincode to the Fabric-based blockchain. Same for nodes and the consensus.

However, the blockchain is simulated when you run your Composer tests.