Channel Creation & Joining

This is a basic tutorial on creating and joining on a channel.

Note

This tutorial currently demonstrates an example of 3 organizations. However the same steps shall be followed for up to N organizations. The commands to create and join a channel, add and sign the configuration of another organization can be run as given below in the example.

Example:

To create a channel:

./fabric-network.sh create-channel <CHANNEL_PROFILE> <CHANNEL_NAME>

To join a peer to a channel:

./fabric-network.sh join-channel-peer <PEER_NO> <CHANNEL_NAME>

To add configuration of another organization:

./fabric-network.sh add-org-config <CHANNEL_NAME> <ORG_TO_BE_ADDED_NAME>

To sign configuration of another organization:

./fabric-network.sh add-org-sign <CHANNEL_NAME> <ORG_TO_BE_SIGNED_NAME>

Build channel configuration via configtx.yaml

A channel is created by building a channel transaction that specifies the initial configuration of the channel. The channel configuration has the information about the channel members(organizations), ordering nodes that can add new blocks to the channel and the policies that govern the channel updates. A channel is created by using the configtx.yaml file and the configtxgen tool. The configtx.yaml file contains the information that is required to build the channel configuration. The configtxgen tool reads the information in the configtx.yaml file and writes it in a special format that can be read by Fabric. In a channel, changes and updates are need to be approved by majority of channel members(organizations). How this approval would take place is in the policies defined inside the channel section of the configtx.yaml. As it can be seen above that we use the argument <CHANNEL_PROFILE> and <CHANNEL_NAME> in the commands to create and join a channel and to add a new channel member(organization) to the channel. The channel profiles are read by the configtxgen to build a channel configuration. Each profile uses YAML syntax to gather data from other sections of the file. The configtxgen tool uses this configuration to create a channel creation transaction for an applications channel, or to write the channel genesis block for a system channel.

A detailed documentation about the chanel configration using configtx.yaml file and the configtxgen tool. can be found here.

As shown below, we define and use a channel profile called ChannelAll.

Channel: &ChannelDefaults
    Policies:
        Readers:
            Type: ImplicitMeta
            Rule: "ANY Readers"
        Writers:
            Type: ImplicitMeta
            Rule: "ANY Writers"
        Admins:
            Type: ImplicitMeta
            Rule: "MAJORITY Admins"
    Capabilities:
        <<: *ChannelCapabilities

Profiles:

    OrdererGenesis:
        <<: *ChannelDefaults
        Orderer:
            <<: *OrdererDefaults
            OrdererType: etcdraft
            EtcdRaft:
                Consenters:
                - Host: orderer0.t-systems.com
                Port: 7050
                ClientTLSCert: crypto-config/ordererOrganizations/t-systems.com/orderers/orderer0.t-systems.com/tls/server.crt
                ServerTLSCert: crypto-config/ordererOrganizations/t-systems.com/orderers/orderer0.t-systems.com/tls/server.crt
            Addresses:
                - orderer0.t-systems.com:7050
            Organizations:
            - *OrdererOrg
            Capabilities:
                <<: *OrdererCapabilities
        Consortiums:
            BaseConsortium:
                Organizations:
                    - *MMS
    ChannelAll:
        Consortium: BaseConsortium
        <<: *ChannelDefaults
        Capabilities:
            <<: *ChannelCapabilities
        Orderer:
            <<: *OrdererDefaults
            OrdererType: etcdraft
            EtcdRaft:
                Consenters:
                - Host: orderer0.t-systems.com
                Port: 7050
                ClientTLSCert: crypto-config/ordererOrganizations/t-systems.com/orderers/orderer0.t-systems.com/tls/server.crt
                ServerTLSCert: crypto-config/ordererOrganizations/t-systems.com/orderers/orderer0.t-systems.com/tls/server.crt
            Addresses:
                - orderer0.t-systems.com:7050
            Organizations:
            - *OrdererOrg
            Capabilities:
                <<: *OrdererCapabilities
        Application:
            <<: *ApplicationDefaults
            Organizations:
                - *MMS
            Capabilities:
                <<: *ApplicationCapabilities

Organization 1

To create a channel run following command. This commands creates the channel from the anchor peer i.e. of oganization 1 and also make it join this new channel.

$ ./fabric-network.sh create-channel ChannelAll channelall

Organization 2

To Add Org 2 configuration in the channel copy Org2.json file in channel-artifacts folder of Org1 and run following commands. Usually add-org-config and add-org-sign are supposed to run from 2 different Orgs (depending upon channel configuration in configtx.yaml), but in this case since we only have Org1 currently added in this channel we can make an exception and add & sign both from Org1. But it would not be possible if there are more than 1 Orgs on a particular channel.

$ ./fabric-network.sh add-org-config channelall Org2

$ ./fabric-network.sh add-org-sign channelall Org2

The channel channelall has been updated with the new organization and new genesis block is now added in ./channel-artifacts/channelall.block file Copy this file ./channel-artifacts/channelall.block in new organization’s channel-artifacts and join this channel from Org2

To join a channel by anchor peer i.e. peer0 of Org2 whose configuration is already added and signed, copy .block file from Org1 in channel-artifacts folder and run the following command. You can run this command for each peer of Org2 to join the channel by changing peer in the argument.

$ ./fabric-network.sh join-channel peer0 channelall

Organization 3

To Add Org 3 configuration in the channel copy Org3.json file in channel-artifacts folder of Org2 and run following commands. Now add-org-config and add-org-sign would from 2 different Orgs (depending upon channel configuration in configtx.yaml), as now there are more than 2 Orgs on channelall.

$ ./fabric-network.sh add-org-config channelall Org3

  1. The new organization configuration for this channel is exported in channel-artifacts/Org3_update_in_envelope.pb file

  2. Copy channel-artifacts/Org3_update_in_envelope.pb file in channel-artifacts folder of any other Org in this channel i.e. Org1

  3. run the command ./fabric-network add-org-sign from any other organization on this channel to sign this configuration and commit to ledger i.e. Org1

To Sign Org 3 configuration added by Org2 in step 5, copy channel-artifacts/Org3_update_in_envelope.pb file in channel-artifacts folder and run following command

$ ./fabric-network.sh add-org-sign channelall Org3

The channel channelall has been updated with the new organization and new genesis block is now added in ./channel-artifacts/channelall.block file. Copy this file ./channel-artifacts/channelall.block in new organization’s channel-artifacts folder and join this channel from anchor peer cli.

To join a channel by anchor peer i.e. peer0 of Org3 whose configuration is already added and signed, copy .block file from Org1 in channel-artifacts folder and run the following command. You can run this command for each peer of Org3 to join the channel by changing peer in the argument.

$ ./fabric-network.sh join-channel peer0 channelall