Ordering Service FAQ

General

Question: I have an ordering service up and running and want to switch consensus algorithms. How do I do that?
Answer: This is explicitly not supported.

Question: What is the orderer system channel?
Answer: The orderer system channel (sometimes called ordering system channel) is the channel the orderer is initially bootstrapped with. It is used to orchestrate channel creation. The orderer system channel defines consortia and the initial configuration for new channels. At channel creation time, the organization definition in the consortium, the /Channel group's values and policies, as well as the /Channel/Orderer group's values and policies, are all combined to form the new initial channel definition.

Question: If I update my application channel, should I update my orderer system channel?
Answer: Once an application channel is created, it is managed independently of any other channel (including the orderer system channel). Depending on the modification, the change may or may not be desirable to port to other channels. In general, MSP changes should be synchronized across all channels, while policy changes are more likely to be specific to a particular channel.

Question: Can I have an organization act both in an ordering and application role?
Answer: Although this is possible, it is a highly discouraged configuration. By default the /Channel/Orderer/BlockValidation policy allows any valid certificate of the ordering organizations to sign blocks. If an organization is acting both in an ordering and application role, then this policy should be updated to restrict block signers to the subset of certificates authorized for ordering.

Question: I want to write a consensus implementation for Fabric. Where do I begin?
Answer: A consensus plugin needs to implement the Consenter and Chain interfaces defined in the consensus package. There are two plugins built against these interfaces already: solo and kafka. You can study them to take cues for your own implementation. The ordering service code can be found under the orderer package.

Question: I want to change my ordering service configurations, e.g. batch timeout, after I start the network, what should I do?
Answer: This falls under reconfiguring the network. Please consult the topic on configtxlator.

Question: How can I deploy Solo in production?
Answer: Solo is not intended for production. It is not, and will never be, fault tolerant.

Question

How do I remove a node from the ordering service?

Answer

This is a two step-process:

Add the node's certificate to the relevant orderer's MSP CRL to prevent peers/clients from connecting to it.
Prevent the node from connecting to the Kafka cluster by leveraging standard Kafka access control measures such as TLS CRLs, or firewalling.

Question: I have never deployed a Kafka/ZK cluster before, and I want to use the Kafka-based ordering service. How do I proceed?
Answer: The Hyperledger Fabric documentation assumes the reader generally has the operational expertise to setup, configure, and manage a Kafka cluster (see kafka-caveat). If you insist on proceeding without such expertise, you should complete, at a minimum, the first 6 steps of the Kafka Quickstart guide before experimenting with the Kafka-based ordering service.

Question: Where can I find a Docker composition for a network that uses the Kafka-based ordering service?
Answer: Consult the end-to-end CLI example.

Question: Why is there a ZooKeeper dependency in the Kafka-based ordering service?
Answer: Kafka uses it internally for coordination between its brokers.

Question: I'm trying to follow the BYFN example and get a "service unavailable" error, what should I do?
Answer: Check the ordering service's logs. A "Rejecting deliver request because of consenter error" log message is usually indicative of a connection problem with the Kafka cluster. Ensure that the Kafka cluster is set up properly, and is reachable by the ordering service's nodes.

Question: When is a BFT version of the ordering service going to be available?
Answer: No date has been set. We are working towards a release during the 1.x cycle, i.e. it will come with a minor version upgrade in Fabric. Track FAB-33 for updates.