fabric-network: How to use the discovery service

This tutorial illustrates the use of the service discovery by the Hyperledger Fabric Node.js fabric-network SDK.

For more information on:

The following assumes an understanding of the Hyperledger Fabric network (orderers and peers), and of Node application development, including the use of the Javascript promise and async await.

Overview

The service discovery provided by the Hyperledger Fabric helps an application understand the current view of the network. Service discovery also has insight into the endorsement policies of chaincodes and is able to provide lists of peers that are currently active on the network that could be used to endorse a proposal. To use the discovery service, the application will have to define just one peer.

fabric-network APIs that can use the service discovery

  • gateway.connect - This method has been enhanced by adding the discovery options.
  • gateway.getNetwork - This method will initialize the network channel using the discovery options from the gateway connect.
  • contract.addDiscoveryInterest - This method will add collections and/or additional chaincodes and collections to the discovery interests to be used by the peer's discovery service when building an endorsement plan. This allows the plan to be built based on the policy information of the contract's chaincodes and collections.
  • contract.submitTransaction - When discovery is enabled by the gateway.connect options, this method will use discovery to help endorse the proposal.
  • transaction.submit - - When discovery is enabled by the gateway.connect options, this method will use discovery to help endorse the proposal.
  • contract.evaluateTransaction - When discovery is enabled by the gateway.connect options, this method will select from the peers that have been discovered during the network channel initialization.
  • transaction.evaluate - When discovery is enabled by the gateway.connect options, this method will select from the peers that have been discovered during the network channel initialization.

fabric-network gateway.connect DiscoveryOption settings

  • discovery.enabled - boolean - True if discovery should be used; otherwise false.
  • discovery.asLocalhost - boolean - Convert discovered host addresses to be 'localhost'. Will be needed when running a docker composed fabric network on the local system; otherwise should be disabled.

To use

By default the fabric-network will not use the service discovery. To enable the use of discovery, set the discovery 'enabled' attribute to a value of true.

await gateway.connect(connectionProfile, {discovery: { enabled: true, asLocalhost: false}});
const network = await gateway.getNetork('mychannel');

To use with docker-compose

When the fabric network is running in a docker-compose and the node.js application is running outside of the docker containers, it will be necessary to modify the addresses returned from the discovery service. The discovery service sees the addresses of the peers and orderers as host names and ports as they exist in the virtual systems, however the node.js application running outside of docker will only know the endpoints as localhost and port. In the docker-compose file, notice how Docker is mapping the port addresses, these must be same when using service discovery. Using - 7061:7051 will not work as the application does not have visibility into the virtual system and the port address as seen by the peer's discovery service.

Use the asLocalhost with true or false, the default is true.

await gateway.connect(connectionProfile, {discovery: { enabled: true, asLocalhost: true}});
const network = await gateway.getNetork('mychannel');

Notice in the following definition of a peer from a docker-compose file. The port number is the same and has been defined along with the host name peer0.org1.example.com:7051 for the peer and gossip settings. The node.js fabric-client application running outside of of the docker containers will use localhost:7051. There is a mapping of the host name to 'localhost' but there is no mapping of the port address.

peer0.org1.example.com:
  container_name: peer0.org1.example.com
  image: hyperledger/fabric-peer
  environment:
	- CORE_VM_ENDPOINT=unix:///host/var/run/docker.sock
	- CORE_PEER_ID=peer0.org1.example.com
	- CORE_PEER_ADDRESS=peer0.org1.example.com:7051
	- CORE_PEER_LISTENADDRESS=peer0.org1.example.com:7051
	- CORE_PEER_GOSSIP_ENDPOINT=peer0.org1.example.com:7051
	- CORE_PEER_GOSSIP_EXTERNALENDPOINT=peer0.org1.example.com:7051
	- FABRIC_LOGGING_SPEC=debug
	## the following setting redirects chaincode container logs to the peer container logs
	- CORE_VM_DOCKER_ATTACHSTDOUT=true
	- CORE_PEER_LOCALMSPID=Org1MSP
	- CORE_PEER_MSPCONFIGPATH=/etc/hyperledger/msp/peer
	##
	- CORE_PEER_TLS_ENABLED=true
	- CORE_PEER_TLS_CLIENTAUTHREQUIRED=true
	- CORE_PEER_TLS_KEY_FILE=/etc/hyperledger/msp/peer/tls/key.pem
	- CORE_PEER_TLS_CERT_FILE=/etc/hyperledger/msp/peer/tls/cert.pem
	- CORE_PEER_TLS_ROOTCERT_FILE=/etc/hyperledger/msp/peer/cacerts/org1.example.com-cert.pem
	- CORE_PEER_TLS_CLIENTROOTCAS_FILES=/etc/hyperledger/msp/peer/cacerts/org1.example.com-cert.pem
	# # the following setting starts chaincode containers on the same
	# # bridge network as the peers
	# # https://docs.docker.com/compose/networking/
	- CORE_VM_DOCKER_HOSTCONFIG_NETWORKMODE=fixtures_default
  working_dir: /opt/gopath/src/github.com/hyperledger/fabric
  command: peer node start
  ports:
	- 7051:7051
  volumes:
	  - /var/run/:/host/var/run/
	  - ./channel/crypto-config/peerOrganizations/org1.example.com/peers/peer0.org1.example.com/:/etc/hyperledger/msp/peer
  depends_on:
	- orderer.example.com

using chaincode to chaincode calls and collections

The peer's discovery service will required information on the channel, chaincodes, and collections that are involved in the smart contract to develop a valid endorsement plan. The contract's channel name and chaincode name will be automatically sent to the peer's discovery service unless the contract indicates that it requires other chaincodes and collections. These are known as 'discovery interests' to the peer's discovery service.

If the endorsement will require one or more chaincode to chaincode calls and/or be over collections, then the application must tell the contract object instance of these names. This will assist the discovery service in putting together an endorsement plan based on all the endorsement policies of the chaincodes and collections involved and the active peers on the network. The endorsement plan will include those peers that satisfy the endorsement policies and the collection policies.

The following examples show how to add to the discovery interests when the chaincode is in one or more collections or the chaincode is calling other chaincodes.

// --------- example 1 --------------------------------------------
// when the smart contract's chaincode will be calling another chaincode
const contract = network.getContract('mychaincode1');
// this adds to the interests
contract.addDiscoveryInterest({name: 'mychaincode2'});

// produces discovery interests of:
[ {name: 'mychaincode1'},
  {name: 'mychaincode2'} ]
// --------- example 2 --------------------------------------------
// when the smart contract's chaincode is in a collection
const contract = network.getContract('mychaincode1');
// this adds the collection name to the contract's chaincode interest
contract.addDiscoveryInterest({name: 'mychaincode1', collectionNames: ['mycollection1']});

// produces discovery interests of:
[ {name: 'mychaincode1', collectionNames: ['mycollection1']} ]
// --------- example 3 --------------------------------------------
// when the smart contract's chaincode is in multiple collections
// and will be calling another chaincode that is in
// multiple collections
const contract = network.getContract('mychaincode1');
// this adds the collection names to the contract's chaincode interest
contract.addDiscoveryInterest({name: 'mychaincode1', collectionNames: ['mycollection1', 'mycollection2']});
// this adds to the interests
contract.addDiscoveryInterest({name: 'mychaincode2', collectionNames: ['mycollection1', 'mycollection2']});

// produces discovery interests of:
[ {name: 'mychaincode1', collectionNames: ['mycollection1', 'mycollection2']},
  {name: 'mychaincode2', collectionNames: ['mycollection1', 'mycollection2']} ]

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.