Ordering Service

Many distributed blockchains, such as Ethereum and Bitcoin, are not permissioned, which means that any node can participate in the consensus process, wherein transactions are ordered and bundled into blocks. Because of this fact, these systems rely on probabilistic consensus algorithms which eventually guarantee ledger consistency to a high degree of probability, but which are still vulnerable to divergent ledgers (also known as a ledger “fork”), where different participants in the network have a different view of the accepted order of transactions.

Hyperledger Fabric works differently. It features a node called an orderer (it’s also known as an “ordering node”) that does this transaction ordering, which along with other orderer nodes forms an ordering service. Because Hyperledger Fabric’s design relies on deterministic consensus algorithms, any block validated by the peer is guaranteed to be final and correct. Ledgers cannot fork the way they do in many other distributed and permissionless blockchain networks. See more about ordering services in the Hyperledger Fabric documentation

Every network begins with an ordering system channel. The policies in the ordering system channel configuration blocks govern the consensus used by the ordering service and define how new blocks are created.

The system channel also contains information about the organizations that are the members of the ordering service (orderer organizations) and those allowed to create new channels (consortium organizations).

See how to create a system channel here.

Starting from version 2.0, the Hyperledger Fabric blockchain only supports Raft consensus, therefore, Catalyst Blockchain Manager also only supports the Raft protocol. Raft is a crash fault-tolerant consensus protocol that allows multiple non-trusting organizations to reach a mutual agreement through a leader-follower concept.

You need to achieve the quorum to keep an ordering service functional. The quorum is the minimum number of working orderers (or, using Raft terminology - consenters) required to ensure effective consensus. For every consenter set, this is a majority of nodes. For instance, an ordering service with 5 nodes requires 3 nodes to make a quorum (if 3 nodes out of 5 fail, a quorum won’t be achieved), 2 node service requires 2 nodes available, and so on. To read more about Raft concepts, click here.

To create an ordering node, you should first create an ordering set. The ordering set is the entity introduced by Catalyst Blockchain Manager as a template for ordering nodes. Using this feature, configurations that you specify when creating an ordering set will apply to all the orderers within this ordering set.

An ordering node (or an orderer) is one of the main entities of Hyperledger Fabric. Orderers are responsible for maintaining the system and application channels, ordering transactions, and packaging them into blocks.

To create an ordering set, go to the Orderers page. Click on the “Create ordering set” button. It will open a menu on the right side of the screen, as shown in the figure below, where you have to provide the following information:

After creating an ordering set, you can create ordering nodes. The process of creating an ordering node is explained in the subsequent section.

Under the Orderers tab, you can see the list of your ordering sets. By clicking on an ordering set’s name, the interface will take you to the ordering set details page.

The page contains two sections. In the upper section three actions are available:

To create a new ordering node, you can click on the “Add new node” button in the inner screen’s upper right-hand corner.

When this button is clicked, a new side window appears.

Provide the following details:

You can create a new ordering node (orderer) either through the “Create new node” button on the upper right-hand corner of the ordering set page or when you open the ordering set page (by clicking on the name of the ordering set) and then selecting “Create node.” In either case, you will have to follow the same steps as mentioned in the section above.

After you successfully add a new ordering node, you can see it under the “Orderers” tab. Any new ordering nodes created have the pending status along with the “No genesis block” button. The “pending” status gets changed to “running” within a few minutes. However, the ordering node will not function in the network before the addition of the genesis block. You need to add the genesis block for the new ordering node to be in sync with the network configuration.

Every ordering node is represented in a box that contains the following details.

When you click on the ordering node, the screen is updated to show only that particular node with its relevant information.

Under this section, you can perform the following actions on the orderer node:

In the lower part of the page, you can see all the recent events and logs with a particular node.

This tab displays events with a particular ordering node.

This tab displays logs of the containers related to a particular ordering node.

You can filter logs by text and/or level.

If you do not want to host any ordering node by your organization due to your business case, you can add an external orderer instead. An external orderer allows you to connect to another orderer which has been already deployed by another organization.

To create an external orderer go to the Orderer tabs. Click the “Create external orderer” button. Provide the name of an external orderer, choose the MSP of the organization that hosts an orderer you want to connect to, and provide the link to this orderer.

To make an orderer functional within a network, you have to add a genesis block containing a system channel configuration. Three cases are possible:

You need to bootstrap a system channel to create a new network.

To join your orderer to an existing network, your organization with this particular orderer has to be added to a system channel beforehand. Please read this section before joining an orderer to a system channel.

To add a genesis block, you can either click on the “No Genesis Block” button at the particular ordering node or click on the “Add genesis block” link from the node’s detailed page.

Two options are available:

You can choose any of these options according to your use case. In both scenarios, you need to follow the steps described here

If you are already a network member (an orderer organization) and you want to add another orderer to the system channel, follow these steps:

Once the ordering node is added to the system channel and successfully fetches a genesis block, you can add it to the application channel as a consenter.

To create a system channel, go to the Orderers page, click the “System channel” button, and click “Create system channel.”

You need to provide the following information.

Orderer organizations represent the list of organizations contributing ordering nodes to the ordering service.

You can add only your organization now and other organizations later, or you can add all the organizations while creating a system channel. In any case, your organization should be present in the orderer organizations list.

To add your organization, you should select its MSP and orderers.

When adding your organization, you can select as many orderers as you want (you need to create these ordering nodes before creating the system channel).

You can add another organization to the orderer organizations list by selecting its MSP and uploading its orderer’s JSON profile (see the screenshot below). Only one orderer can be uploaded for each organization in this case.

The consortium is the list of organizations that can create application channels and be added to the channels upon its creation.

You can add a few organizations to a consortium list or add other organizations later, as described here. In any case, your organization must be added to the consortium.

In this section, you have to configure parameters for a system channel:

By clicking on the System channel button, you can view the system channel you are a member of.

In the upper part of the page, you can check the system channel status. The numbers (X/Y) display how many active orderers (X) are among the consenters’ cluster size (Y).

Each channel including a system channel contains a chain of blocks with transactions. The last system channel’s block contains the actual configuration of a system channel.

You may need to download the last block in a few cases: e.g. for debugging a problem with a system channel to ensure everything is configured correctly or for uploading the genesis block to another orderer to add it to the system channel.

You can download the last block in JSON or protobuf format. The JSON format is human readable. Meanwhile, the protobuf format is needed to share with another organization for joining its orderer to the system channel.

This is the list of the organizations that can create a channel. Under this tab, you can add or remove organizations from the consortium. Any non-consortium members can not create a channel and can not be added to a channel at channel creation. However, the non-consortium members can be added to the channel later by the consortium members.

There are three sections available under this tab

Here is a list of organizations that are added to the system channel as a member of the ordering service. They can add their orderers (consenters) to the channels. You can add organizations as Orderer organizations through the “Add” button or remove organizations by clicking the “Remove” button.

You can see the orderer endpoints here by clicking on the particular organization. Click the “Update ordering” endpoints button if you want to change the endpoints set. You can specify as many endpoints as needed or select no endpoints.

In the Consenters block, you can view the MSPID of the consenters, TLS certificates, and perform specific actions such as adding or removing a consenter. You can also see the consenter’s statuses on a particular channel.

We recommend adding or removing consenters with caution.

Here you can see the information about the channel genesis block configuration along with the "Edit" option.

You can add an organization to the list of orderer organizations in one of two ways.

You need to select the organization from the drop-down menu and provide its orderer JSON profile upload (this JSON profile needs to be exported and shared with you by the organization you will add). Only one orderer can be added for each organization that can be only one at a time.

Click the “Add organization” button. The process is the same as described in the previous section.

You can add an organization to the consortium in one of two ways.

You need to select the organization from the drop-down menu

Click the “Add an Organization” button and select an organization from the drop-down menu.