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Elrond Node Prototype

State Sharding PoC for Elrond network


This readme will give some insight into the code, architecture and several concepts used in this prototype.

Elrond Prototype overview - Progress update #2 - Medium

Table of Contents

Design goal

The purpose of this project is to offer a rapid development iteration twords a state sharded architecture and validate some of the initial hypothesis presented in our paper, while taking the first material steps to transforming our vision of a decentralized, scalable and secure blockchain architecture into working code.

With the validation of our core hypothesis: demonstrating a working model of state sharding and cross-shard transactions, this project has become obsolete and all focus has been moved onto another repository named elrond-go, where the next version of elrond arhitecture is built -> Elrond Testnet v0.1 .

What to expect

This repository was originally created and used to validate several assumptions related to state sharding and cross shard transactions. This can be considered as a sandbox to test various mechanisms as preparation for developing the testnet.

What not to expect

This is not a testnet so expect not all features or functionalities to be available. As our main focus was on validating assumptions regarding sharding and not improvements on performance, there are things that could have been optimised. These will be considered while developing Elrond testnet.

Directory structure

The code is split into two sections:

  • /elrond-api - implementing a web application and the REST APIs allowing elrond client to interact with a node (computer running the Elrond Prototype code)
  • /elrond-core - implements the core part of the Elrond Prototype protocol


P2P communication:

the prototype uses tomp2p for its p2p networking model and communication primitives. Communication is done on channels for the registered topics: Transactions, Blocks, Receipts, Cross Shard transactions, etc. Message relay across channels is currently done by direct send to the registered peers, which is really bad in terms of performance and memory consumption but easy to implement in first phase. This needs to be abstracted on a gossip model at shard level.


the prototype uses cryptographic primitives from spongycastle and implements Schnorr signature scheme for validating transactions and Belare-Neven multisignature scheme for signing and validating block signatures. The multisignature scheme allows for signature aggregation, so no matter how many signers participate in signing a single block the resulting signature is always 64 bytes long.


time is split into epochs, and each epoch is split into rounds. In each round there is a new consensus group created, formed by a block proposer/leader and validators. Each round is again split into subrounds mapped to the consensus phases. Elrond Prototype focuses more on what happens during rounds and subrounds, so the epoch actions are not yet implemented.


the consensus mechanism used in the prototype is a round robin mechanism where each node takes turns in proposing blocks. Although the random sampling of proposer and validators is already implemented in a separate branch, changes to the PBFT consensus still have to be operated. The switch to PBFT consensus and selection of validators will be done as soon as the branch is ready - put on hold as decided to switch to Go for the testnet. PBFT Consensus will be first implemented in testnet repository.

Data layer:

main data models implemented: Block, Receipt, Transaction, Account, Trie etc. For serialization we are currently using either json or Ethereum's RLP. Probably we will switch to either protobufs or capn'proto in testnet for the performance boost, but this is not relevant in the prototype. For persistent storage we are currently using LevelDB while for non-persistent storage LRU maps or Guava Cache.


Phase 1 - we are using a static sharding model where we need to define an initial number of shards. State is currently sharded, each shard maintains only accounts associated to its shard and the corresponding blockchain. For the time being nodes will be placed in shards according to their PK using the same allocation mechanism as for dispatching transactions - will be changed when implementing epoch events. Notarization chain is not yet implemented - relaying cross shard transactions is done through messaging in cross shard communication channels. This will no longer be needed after the introduction of the notarization chain, as our dispatching of transactions takes care of the availability in destination shard, and the inclusion proofs take care of validation (Merkle proofs will be replaced with accumulators)

Execution layer:

Includes several executors: bootstrapping, synchronization and chronology tasks (proposals and validations) + transaction and block execution, account state rollback. Interceptors: blocks, receipts, transactions, cross shard transactions.

How to run a node

You can run an Elrond Prototype node either through Swagger, or by using the elrond-wallet For this you need first to run the elrond-api jar.


To build the jar you should go to root folder and run ''' $ mvn package '''

This will generate a jar '''/elrond-api/target/elrond-api-1.0-SNAPSHOT.jar''' that you can run then with: ''' java -jar ./elrond-api/target/elrond-api-1.0-SNAPSHOT.jar '''

Wait until you you get a message like

''' Started ElrondApiApplication in 15.48 seconds (JVM running for 17.733) '''

Now you should be ready to either launch the elrond-wallet or start using the swagger. To use swagger open a browser page and go to : http://localhost:8080/swagger-ui.html

In elrond-node-controller you can find all currently available REST APIs.

To start the node you should use the '''/node/start''' REST API

Take care about the port and Ip you are using. The first instance you start should be the master node, so port and master peer port should be the same, and ip address should be the ip of the machine you are running on, or localhost. The subsequent nodes should use for the masterPeerPort and masterPeerIpAddress the ones from the first node. If you are trying to run multiple node instances on the same machine, you can start the elrond-api for other instances but you need to change the port (default is 8080) ''' java -jar ./elrond-api/target/elrond-api-1.0-SNAPSHOT.jar --server.port=8081 '''

Now you can start swagger on the new port to configure and start the new elrond prototype node instance http://localhost:8081/swagger-ui.html

One difference between a master node and a peer node (not master node) instance is that the master receives in its account the entire balance in the system, all other nodes start up with 0 balance. There are some other functionalities working only on the first instance, such as benchmarking all shards. This is also the reason why each new connecting node should connect to the network through this master node. If benchmarking shards is not required, then subsequent nodes can connect to the network through any other already connected node.


Official website:

Elrond whitepaer: