I built hyperledger fabric network using Kafka-based Ordering Service.
I thought that Orderer doesn't have Block data.
But, when I checked /var/hyperledger/production/orderer/chains/mychannel in Orderer server, I found blockfile_000000 file.
I checked this file using "less" command.
Then, I found key-value data which I registered by invoking chaincode.
What is this file?
This means that Orderer also maintain Block data(i.e. Ledger)?
The orderer has the blockchain of all channels it is part of.
However, it doesn't have the world state and it doesn't inspect the content of the transactions.
It just writes the blocks into the disk, to serve peers that pull the blocks from it.
Related
Here is the log of Hyperledger Fabric test network. There are 2 peer node(peer0.org1.example.com & peer0.org2.example.com) and 2 orderer node(orderer.example.com & orderer2.example.com).
My question is what 「writeBlock」,「StoreBlock」，「Validate」「commit」stage actually does? I know that at 「propose」stage, a chosen orderer(in this case, orderer.example.com) will create a block and then send the created block to other orderer such as orderer2.example.com. However, I don't understand what orderers does at「writeBlock」stage. Do they sign the created block at 「writeBlock」stage? Next, peer nodes received the block from who? orderer.example.com or orderer2.example.com? In my guess, I think it's from orderer.example.com but I'm not sure.
I don't understand what orderers does at「writeBlock」stage.
I'm not sure about those stages (writeBlock looks self-explanatory). I don't know about "StoreBlock", it isn't mentioned in the official docs. I'm wondering which Fabric version you are using.
Next, peer nodes received the block from who?
In a RAFT network you have a leader/follower model. You can think of a leader peer as an entry point/doorman for all communication coming from the ordering nodes. An ordering node sends blocks to the leading peer(s) of each organization; the leading peer is then responsible for distributing those blocks to other peers belonging to the same organization. Distribution is done using gossip protocol.
Hyperledger Fabric is a complex system, with many components and a lot of moving parts.
The log that you are referring to is the log of the orderer node - orderer.example.com. It's a part of the Fabric test network. You can see what's happening in detail by looking at the logs of other Fabric components, such as peer node logs.
The Fabric network has a set of orderer nodes, which are responsible for ordering the transactions and creating blocks in the blockchain.
The orderer nodes are configured to use a consensus algorithm (such as Solo or Kafka) to achieve a consensus about the order of the transactions.
A Fabric network has a set of peer nodes, which are responsible for executing the chaincode (smart contracts) and catching and validating the transactions.
The Fabric test network consists of one orderer node, which is configured to use Solo consensus algorithm. This orderer node is orderer.example.com.
The Fabric test network consists of two peer nodes, which are peer0.org1.example.com and peer0.org2.example.com.
The log that you are referring to is the log of the orderer node - ord
In Hyperledger Fabric, what is the expected behavior of peer when all orderer nodes are down.
Should peer also down, or stop serving request from client, or continue to serve query request?
In our test, after orderers are stopped, the peer keeps writing "failed to create connection to orderer" log. When we query a key by calling chaincode the value is returned.
Can you help clarify if this is expected behavior. Thank you.
I am working on a distributed hyperledger fabric network. I would recommend the Orderer Raft Consensus https://hyperledger-fabric.readthedocs.io/en/release-2.2/orderer/ordering_service.html#ordering-service-implementations.
I have solved this in such a way that in my case I have three orderers that run independently on different environments.
If I crash all these orderers, the peer containers will continue to run on the other participants of the network. As you said, they cannot make any transactions.
If one of my orderers crashes it is not so bad after the raft consensus, the containers keep running. If another one fails, no transactions can be made. In this case I let the peers continue and check if the orderers are available again.
The behaviour you described I would put down to the fact that the peer requests the value from his ledger, he doesn't need an orderer for that. https://hyperledger.github.io/fabric-chaincode-node/master/api/fabric-shim.ChaincodeStub.html#getState
Have a read of this: https://github.com/hyperledger/fabric/blob/master/docs/source/peers/peers.md This is the best documentation for how the system works I've found and there's more in the docs directory on the repo for orderers, etc.
My understanding is: The peers are there to sign (endorse) transaction proposals. The orderer exists to order, validate, package and distribute transactions to peers. The peers can also distribute their knowledge of validated transactions via the gossip channel.
If all orderers go down, the transactions will not be validated/packaged/distributed so the blockchain will be out of action until the orderers are restored.
When we query a key by calling chaincode the value is returned.
Peers will still remain up and ready to sign/endorse transaction proposals, and querying the blockchain held at the peers will still work. Chaincodes are hosted by the peers. Orderers do not host chaincode.
Also see here https://github.com/hyperledger/fabric/blob/master/docs/source/orderer/ordering_service.md#ordering-service-implementations for the various modes the orderer can be run in: Raft mode, Kafka ordering, Solo ordering.
I think the current observerd behavour is expected and in my view it is just fine.
Let's check the purpose of orderer?
Order the transactions
Cut the block and distribute the block amongst the orgs when the criteria is met ( min txn/size or time).
This also means, orderer is needed when your Fabric network is processing those transactions which intend to write data into the ledger, isnt it? And Query is not a transaction which writes into the ledger. So it doesn't need the orderer. For query, it will pick up the data from the peer's local database.
So I think what could be done is, to send out an alert to the production support when your application detect orderer node down ( with some health check ? ). And your application displays a dimnished capacity/limited operations message while work on bringing up the orderer network, the system can still serve the search queries.
From my view, its just fantastic. But its finally upto you. Cheers!!
Consider the following situation:
I am running fabric-samples/first-network for the HLF in RAFT mode.
I use the CLI container to fetch the latest block for mychannel and edit the OrdererAddresses section by removing 4 orderers namely, orderer2.example.com, orderer3.example.com, orderer4.example.com, orderer5.example.com from it.
I am assuming this should disturb RAFT protocol because orderers are meant to communicate with one another by looking at the endpoints in OrdererAddresses section.
Now, the issue is that, despite the above fact, the RAFT keeps working fine. I wait for 10 minutes, assuming RAFT would break after EvictionSuspicion timeout as no longer leader can comunicate to other orderers. But this does not happen. I am still able to read blocks from the mychannel as well as I am able to submit new transactions (invoke operations) on the chaincode on that channel.
This means that OrdererAddresses are not looked into while communicating. Please correct me if I am wrong. By this, I need to know:
What is the exact functionality of OrdererAddresses section in the RAFT channels?
I learnt that RAFT orderers communicate to one another using the
host and port properties of the Consenters section for the
purpose of consensus messages. The endpoints present in the
OrdererAddresses section are used for replication of blocks.
The learning could be verified from here as answered by Yacov M.
I have hyper-ledger fabric setup with 2 organisation which works well.I am keeping the separate storage for the blocks state in file system. Now i turn down the all organisation container, all the states inside the container is deleted, but i am keeping states which are stored the my file path. Next, when i use the existing file storage, and turn up the docker, all the peers and ordered load well from the state which i was stop. The problem here is, I am unable to reinitiate the channel transaction and i am unable to join the same channel from the peer. where does the mychannel.block get stored. when i try to join the channel i get error
2019-11-27 03:49:01.631 UTC [channelCmd] InitCmdFactory -> INFO 001 Endorser and orderer connections initialised
Error: genesis block file not found open mychannel.block: no such file or directory
You should know what volumes are you using to persist that file.
You should persist:
/var/hyperledger/production in your orderers and peers.
/opt/couchdb/data in your CouchDB containers.
Wherever you store your MSP, TLS files and other configuration files (genesis block, etc.). Only you know about your configuration.
/var/lib/postgresql/data in your CA's PostgreSQL container.
Whatever other file/folder you want to persist.
Anyway, I don't know if I have understood you, but if you persist all these, you don't need to join a channel again, the peers remain joined after restarting the network.
Does the gossip protocol is used only to spread the committed blocks via all peers on the "order" stage? Does it work on the “execute” stage, when the endorsing peers execute and sign the transactions?
The gossip component is the peer's communication layer, and it contributes to the block dissemination via having peers distribute blocks among themselves instead of having all of them pull them directly from the orderer nodes.
It works roughly like this:
When the orderer cuts a new block, it appends it to its local file system.
In every organization, there is usually a peer that is selected among the peers in its organization (for that channel) to pull blocks from the orderer, and forward them to other peers in its organziation. The other peers also forward the blocks even further to other peers, etc. etc. and this all happens via a "gossip" style protocol.
I recommend that you read the gossip section in the documentation.