I'm new to Blockchain and trying to understand if Hyperledger platforms (such as Fabric and Sawtooth) offer full/light nodes separation like Ethereum.
Thanks.
Don't know about STL, but Fabric doesn't have a light node.
There are 2 reasons for this:
1) The hash in the block header is simply a concatenated hash over the block data, and not a Merkle tree root. So you cannot prove efficiently that a Transaction exists in a block, without giving the entire block.
2) Unlike most Blockchains, Fabric is an execute-order Blockchain, which means that some transactions in the block may not be valid at all, and only at the time of commit, the peer checks if they are valid.
Related
I want to ask about blockhain Hyperledger Fabric. Is it possible to let Peer nodes to do Orderer node's task which is packing the transaction into new block?
I kind of think the orderer node is kind of a redundant node since for example in Bitcoin network, the packing of the transactions into block and the verification of new transaction is solely done by the full node(miner node).
Can anyone give me justification why there should be orderer's node in the Hyperledger Fabric?
And if I were to build my project on Hyperledger network and forgo orderer node(which means the peer node will do both the verification of transaction and the packing of transaction) is it possible?
Please tell me your thoughts and ideas.
Thank you.
TL;DR
HLF by design is deterministic so the orderer nodes are important. Only they participate in consensus not all peers and the blocks they produce are Final (Not prone to forks).
No you cannot make a peer orderer as well. Your network configuration for HLF must have at least one orderer to work
Hyperledger Fabric (HLF) vs Bitcoin
HLF is a private permissioned blockchain where as Bitcoin is a public permissionless blockchain. You should not expect them to work similarly.
Public blockchains
In public blockchain for example bitcoin everyone is treated equal in other words no one have special privileges you may think well miner are the ones minning block but the important point is anyone can become miner its open game no restriction on who can become miner or who can run a node etc.
Private Blockchain
In private blockchain for example HLF roles are predefined at the time of setting up and starting blockchain. Each role has certain tasks and privileges and restriction. The no of organisations peers, endorser peers, orderers, channels all are predefined and some have special privileges which no other role has like orderer whose is responsible for receiving endorsed transactions from peers and put them into blocks then these blocks are distributed to all peers. These blocks are Final.
But Why?
Private Blockchains (Like HLF) full-fill special use cases for example supply chain, B2B operations In such use cases one may want to harness positives of blockchain like transparency, auditing, provenance but may also want some sort of role based access or restrictions of certain data to certain audience public blockchains like Ethereum and bitcoin does not fit here.
Now coming toward your question
Why is there an orderer node in HLF isn't it redundant ?
No it's not redundant, HLF has deterministic consensus algorithms where as Ethereum and Bitcoin have probabilistic consensus algorithms which means there can be ledger forks. In HLF there are no Ledger forks because fork occur when two equal participants have conflict at a common point. Incase of HLF the participants are not equal as peers cannot participate in consensus process the block order set by orderers is Final. And rightfully so because for the use cases it is designed for does not want forks and want to have special roles and much much more transaction throughput.
Must must Read !
https://hyperledger-fabric.readthedocs.io/en/release-2.2/orderer/ordering_service.html#what-is-ordering
No it is not possible to assign peers orderer's role you must have at least 1 orderer in your HLF network to work.
I am new to the latest Hyperledger fabric 2. Before deprecating fabric-composer (a very well thought and intuitive framework) if you wanted to add multiple assests you could call AssetRegistry.addAll() method to add not just one asset but an array of assets. Is there an equivalent in the new hlf version 2? If I have an array of assets/states that I want added in the world-state database and I call putState() multiple times for each state/asset is it not less efficient than calling a putStateList() method that would take as param an array of states? (BTW the old naming of asset from the times of hyperledger composer is much more intuitive than the new name of state ... composer vs de-composer :)))
There is no putStateList in Hyperledger Fabric.
As you mentioned, the only way is to call PutState the number of times you want.
In terms of performance, the data to be sent by the chaincode to the peer is the same length, but I understand that if Peer node could accept a list of states, it could be more efficient on the server-side.
If we look at the internals of Node.JS library, we can see that handlePutState connects to the peer and waits:
And then, it will send the message to the peer, writing the msg to the stream:
Suppose I have started fabric with two peers in a single organization. After running my application/rest-server through composer and submitting transactions. I was able to make changes in the values of Couchdb instance of peer1 by going on the address http://localhost:6984/_utils/#/_all_dbs. Now, the two peers are not in sync with each other - application should throw some error but it isn't. Mostly, because it is getting data just from the first peer i.e. peer1.
So, firstly how can I get data from multiple peers - if I want to get data from peer2 aswell?
Secondly, why it is getting data from state database not from ledger?
Thirdly, data should remain in sync even after committed how can I configure this? if some peer tampered its database it should be notified. I have read consensus part and got that it is for the correct order of transactions and blocks but what if someone tampered with the state database?
If you're able to change the entries in state database for 1 peer, with a strong endorsement policy such as AND, your transactions will fail validation because of difference in the data for the two peers. This is one of the most important pros of decentralized network.
State database and the Ledger are not same thing. this should help you in understanding the differences between the both.
Every participating member of a Hyperledger Fabric network is a known entity per se (since Fabric being a permissioned blockchain). Said that, a change in state database of a single peer will again lead to scenario #1 above, where the Read/Write sets in a transaction won't match for multiple peers (as their state databases contain different values of an asset). This will lead to invalidation of the transactions. Now it just becomes a question of how can the network know about the corrupted peer(and subsequent state db). There can be multiple solutions for the same.
But most importantly, Fabric being a permissioned blockchain network, the state databases must be very strictly access protected and authorized outside of the network too.
the fact that you modified the world db doesn't mean anything. any changes you make to that database are not a representation of the ledger.
The ledger itself, the blocks and the transactions they contain are stored in a physical file. The world state db is simply a collection of the current state for each asset. This is a good design because an application will not care about every state change an item went through, it will only care about the current state. The world state db can easily be recreated whenever there is a need for it.
Now, you should not make any changes directly to to the world state db, because that's useless. Any change needs to go through the proper process, via a proposal submitted by a peer which then goes through the orderer. Only when everything is followed, does a change go onto the ledger and get synced with every peer and the world state db will reflect that.
In terms of where you should get the data, the answer is that it doesn't matter. Each peer will have an exact copy of the ledger so if you get data from peer 1 or 2 is irrelevant, it will be the same thing.
Again, just because you changed the world state, that doesn't mean anything, the ledger is untouched, but your application reports the current state from the world state db, which is now incorrect because of your change.
I am wondering that how your data is safe when an admin can change the latest state in Couchdb using Fauxton or cURL provided by Couchdb directly.
According to my understanding Hyperledger Fabric provides immutable data feature and is best for fraud prevention(Blockchain feature).
The issue is :- I can easily change the data in couchdb and when I query from my chaincode it shows the changed data. But when I query ledger by using GetHistoryForKey() it does not shows that change I made to couchdb. Is there any way I can prevent such fraud? Because user will see the latest state always i.e data from couchdb not from ledger
Any answer would be appreciated.
Thanks
You should not expose the CouchDB port beyond the peer's network to avoid the data getting tampered. Only the peer's administrator should be able to access CouchDB, and the administrator has no incentive to tamper their own data. Let me explain further...
The Hyperledger Fabric state database is similar to the bitcoin unspent transaction database, in that if a peer administrator tampers with their own peer’s database, the peer will not be able to convince other peers that transactions coming from it are valid. In both cases, the database can be viewed as a cache of current blockchain state. And in both cases, if the database becomes corrupt or tampered, it can be rebuilt on the peer from the blockchain. In the case of bitcoin, this is done with the -reindex flag. In the case of Fabric, this is done by dropping the state database and restarting the peer.
In Fabric, peers from different orgs as specified in the endorsement policy must return the same chaincode execution results for transactions to be validated. If ledger state data had been altered or corrupted (in CouchDB or LevelDB file system) on a peer, then the chaincode execution results would be inconsistent across endorsing peers, the 'bad’ peer/org will be found out, and the application client should throw out the results from the bad peer/org before submitting the transaction for ordering/commit. If a client application tries to submit a transaction with inconsistent endorsement results regardless, this will be detected on all the peers at validation time and the transaction will be invalidated.
You must secure your couchdb from modification by processes other than the peer, just as you must generally protect your filesystem or memory.
If you make your filesystem world writable, other users could overwrite ledger contents. Similarly, if you do not put access control on couchdb writes, then you lose the immutability properties.
In Hyperledger Fabric v1.2, each peer has its own CouchDB. So even if you change the data directly from CouchDB of one peer. The endorsement would fail. If the endorsement fails, your data will not be written neither in world state nor in the current state.
That's the beauty of a decentralized distributed system. Even if you or someone else changes the state of your database/ledger it will not match with the state of others in the network, neither will it match the transaction block hash rendering any transactions invalid by the endorsers unless you can restore the actual agreed upon state of the ledger from the network participants or the orderer.
To take advantage of the immutability of ledger you must query the ledger. Querying the database does not utilize the power of blockchain and hence must be protected in fashion similar to how access to any other database is protected.
You need to understand 2 things here
Although the data of a couchdb of a peer maybe tampered, you should setup your endorsement policy in such a way that it must be endorsed by all the peers.
You cannot expose your couchdb to be altered, I recommend to see Cilium
As explained by others - endorsements/consensus is the key. Despite the fact that ledger state of an endorsing peer can be modified externally - in that event all transactions endorsed by that peer would get discarded, because other endorsing peers would be sending correct transactions (assuming other's world state was also not tampered with) and consensus would play the key role here to help select the correct transaction.
Worst case scenario all transactions would fail.
Hyperledger fabric's world state (Ledger state) can be regenerated from the blockchain (Transactions Log) anytime. And, in the event of peer failure this regeneration happens automatically. With some careful configuration, one can build a self-healing network where a peer at fault would automatically rise from ashes (pun intended).
The key point to consider here is the Gossip Data dissemination protocol which can be considered as the mystical healer. All peers within the network continuously connect, and exchange data with other peers within the network.
To quote the documentation -
Peers affected by delays, network partitions, or other causes resulting in missed blocks will eventually be synced up to the current ledger state by contacting peers in possession of these missing blocks.
and ...
Any peer with data that is out of sync with the rest of the channel identifies the missing blocks and syncs itself by copying the correct data.
That's why it is always recommended to have more and more of endorsing peers within the network and organizations. The bigger the network - harder it would be beat with malicious intent.
I hope, I could be of some help. Ref Link: https://hyperledger-fabric.readthedocs.io/en/release-1.4/gossip.html
Even though this is plausible, the endorsement policy is the general means by which you protect yourself (the system) from the effects of such an act.
"a state reconciliation process synchronizes world state across peers on each channel. Each peer continually pulls blocks from other peers on the channel, in order to repair its own state if discrepancies are identified."
just playing with Hyperledger Composer, and I'm wondering ,Where is the blockchain physically
I'mean is it binary file , text file ....?
is it portable ?
thank you all
There are two place which "store" data in Hyperledger Fabric (the underlying blockchain infrastructure used by Composer which is a runtime abstraction layer above it):
the ledger
the state database ('World state')
The ledger is the actual "blockchain". It is a file-based ledger which stores serialized blocks. Each block has one or more transactions. Each transaction contains a 'read-write set' which modifies one or more key/value pairs. The ledger is the definitive source of data and is immutable.
The state database (or 'World State') holds the last known committed value for any given key - an indexed view into the chain’s transaction log. It is populated when each peer validates and commits a transaction. The state database can always be rebuilt from re-processing the ledger (ie replaying the transactions that led to that state). There are currently two options for the state database: an embedded LevelDB or an external CouchDB.
As an aside, if you are familiar with Hyperledger Fabric 'channels', there is a separate ledger for each channel.
The chain is a transaction log, structured as hash-linked blocks, where each block contains a sequence of N transactions. The block header includes a hash of the block’s transactions, as well as a hash of the prior block’s header. In this way, all transactions on the ledger are sequenced and cryptographically linked together.
The state database is simply an indexed view into the chain’s transaction log, it can therefore be regenerated from the chain at any time.
Source: http://hyperledger-fabric.readthedocs.io/en/release/ledger.html
Suffice to say, Hyperledger Composer uses Fabric (as the blockchain infrastructure) to endorse/order/commit transactions to blocks on the ledger.
To see the physical location of these data you can go to /var/hyperledger/production in each peer container in your fabric network
Actually, the blockchain is a shared database, which is read-only and append-only. And it is distributed in every peers. So every peer has a copy of the shared database. Normally, LevelDB or CouchDB is used in HyperLedger Fabric.
The ledger is comprised of a blockchain (‘chain’) to store the immutable, sequenced record in blocks, as well as a state database to maintain current fabric state.
Here is more information about HyperLedger Fabric Ledger (the blockchain)
Blockchain is shared among all the peer to peer networks hosting it. So basically blockchain is stored in many HDD all around the world.