Private networks
This guide explains how to set up a private network of multiple ETN-SC nodes. An Electroneum network is private if the nodes are not connected to the main network. In this context private only means reserved or isolated, rather than protected or secure. A fully controlled, private Electroneum network is useful as a backend for core developers working on issues relating to networking/blockchain syncing etc. Private networks are also useful for Dapp developers testing multi-block and multi-user scenarios.
Prerequisites
To follow the tutorial on this page it is necessary to have a working ETN-SC installation (instructions here). It is also helpful to understand ETN-SC fundamentals (see Getting Started).
Private Networks
A private network is composed of multiple Electroneum nodes that can only connect to each other. In order to run multiple nodes locally, each one requires a separate data directory (--datadir). The nodes must also know about each other and be able to exchange information, share an initial state and a common consensus algorithm. The remainder of this page will explain how to configure ETN-SC so that these basic requirements are met, enabling a private network to be started.
Choosing A Network ID
Electroneum Mainnet has Network ID = 51420. There are also many other networks that ETN-SC can connect to by providing alternative Chain IDs, some are testnets and others are alternative networks built from forks of the ETN-SC source code. Providing a network ID that is not already being used by an existing network or testnet means the nodes using that network ID can only connect to each other, creating a private network. A list of current network IDs is available at Chainlist.org. The network ID is controlled using the networkid flag, e.g.
Choosing A Consensus Algorithm
While the main network uses Istanbul Byzantine Fault Tolerant (IBFT) to secure the blockchain, ETN-SC also supports the the 'Clique' proof-of-authority (PoA) consensus algorithm and the Ethash proof-of-work algorithm as alternatives for private networks. Clique is strongly recommended for private testnets because PoA is far less resource-intensive than PoW. The key differences between the consensus algorithms available in ETN-SC are:
Ethash
ETN-SC's PoW algorithm, Ethash, is a system that allows open participation by anyone willing to dedicate resources to mining. While this is a critical property for a public network, the overall security of the blockchain strictly depends on the total amount of resources used to secure it. As such, PoW is a poor choice for private networks with few miners. The Ethash mining 'difficulty' is adjusted automatically so that new blocks are created approximately 12 seconds apart. As more mining resources are deployed on the network, creating a new block becomes harder so that the average block time matches the target block time.
Clique
Clique consensus is a PoA system where new blocks can be created by authorized 'signers' only. The clique consensus protocol is specified in EIP-225. The initial set of authorized signers is configured in the genesis block. Signers can be authorized and de-authorized using a voting mechanism, thus allowing the set of signers to change while the blockchain operates. Clique can be configured to target any block time (within reasonable limits) since it isn't tied to the difficulty adjustment.
Creating The Genesis Block
Every blockchain starts with a genesis block. When ETN-SC is run with default settings for the first time, it commits the Mainnet genesis to the database. For a private network, it is generally preferable to use a different genesis block. The genesis block is configured using a genesis.json file whose path must be provided to ETN-SC on start-up. When creating a genesis block, a few initial parameters for the private blockchain must be defined:
Electroneum platform features enabled at launch (config). Enabling and disabling features once the blockchain is running requires scheduling a hard fork.
Initial block gas limit (gasLimit). This impacts how much EVM computation can happen within a single block. Mirroring the main Electroneum network is generally a good choice. The block gas limit can be adjusted after launch using the
--miner.gastargetcommand-line flag.Initial allocation of ETN (alloc). This determines how much ETN is available to the addresses listed in the genesis block. Additional ETN can be created through mining as the chain progresses.
Clique Example
Below is an example of a genesis.json file for a PoA network. The config section ensures that all known protocol changes are available and configures the 'clique' engine to be used for consensus. Note that the initial signer set must be configured through the extradata field. This field is required for Clique to work.
The signer account keys can be generated using the ETN-SC account command (this command can be run multiple times to create more than one signer key).
The Electroneum address printed by this command should be recorded. To encode the signer addresses in extradata, concatenate 32 zero bytes, all signer addresses and 65 further zero bytes. The result of this concatenation is then used as the value accompanying the extradata key in genesis.json. In the example below, extradata contains a single initial signer address, 0x7df9a875a174b3bc565e6424a0050ebc1b2d1d82.
The period configuration option sets the target block time of the chain.
Ethash Example
Since Ethash is the default consensus algorithm, no additional parameters need to be configured in order to use it. The initial mining difficulty is influenced using the difficulty parameter, but note that the difficulty adjustment algorithm will quickly adapt to the amount of mining resources deployed on the chain.
Initialising the ETN-SC Database
To create a blockchain node that uses this genesis block, first use etn-sc init to import and sets the canonical genesis block for the new chain. This requires the path to genesis.json to be passed as an argument.
When ETN-SC is started using --datadir data the genesis block defined in genesis.json will be used. For example:
Scheduling Hard Forks
As Electroneum protocol development progresses, new features become available. To enable these features on an existing private network, a hard fork must be scheduled. To do this, a future block number must be chosen which determines precisely when the hard fork will activate. Continuing the genesis.json example above and assuming the current block number is 35421, a hard fork might be scheduled for block 40000. This hard fork might upgrade the network to conform to the 'London' specs. First, all the ETN-SC instances on the private network must be recent enough to support the specific hard fork. If so, genesis.json can be updated so that the londonBlock key gets the value 40000. The ETN-SC instances are then shut down and etn-sc init is run to update their configuration. When the nodes are restarted they will pick up where they left off and run normally until block 40000, at which point they will automatically upgrade.
The modification to genesis.json is as follows:
The upgrade command is:
Setting Up Networking
With the node configured and initialised, the next step is to set up a peer-to-peer network. This requires a bootstrap node. The bootstrap node is a normal node that is designated to be the entry point that other nodes use to join the network. Any node can be chosen to be the bootstrap node.
To configure a bootstrap node, the IP address of the machine the bootstrap node will run on must be known. The bootstrap node needs to know its own IP address so that it can broadcast it to other nodes. On a local machine this can be found using tools such as ifconfig and on cloud instances such as Amazon EC2 the IP address of the virtual machine can be found in the management console. Any firewalls must allow UDP and TCP traffic on port 30303.
The bootstrap node IP is set using the --nat flag (the command below contains an example address - replace it with the correct one).
The 'node record' of the bootnode can be extracted using the JS console:
This command should print a base64 string such as the following example. Other nodes will use the information contained in the bootstrap node record to connect to the peer-to-peer network.
If the nodes are intended to connect across the Internet, the bootnode and all other nodes must have public IP addresses assigned, and both TCP and UDP traffic can pass their firewalls. If Internet connectivity is not required or all member nodes connect using well-known IPs, ETN-SC should be set up to restrict peer-to-peer connectivity to an IP subnet. Doing so will further isolate the network and prevents cross-connecting with other blockchain networks in case the nodes are reachable from the Internet. Use the --netrestrict flag to configure a whitelist of IP networks:
With the above setting, ETN-SC will only allow connections from the 172.16.254.0/24 subnet, and will not attempt to connect to other nodes outside of the set IP range.
Running Member Nodes
Before running a member node, it must be initialized with the same genesis file as used for the bootstrap node. With the bootnode operational and externally reachable (telnet <ip> <port> will confirm that it is indeed reachable), more ETN-SC nodes can be started and connected to them via the bootstrap node using the --bootnodes flag. The process is to start ETN-SC on the same machine as the bootnode, with a separate data directory and listening port and the bootnode node record provided as an argument:
For example, using data directory (example: data2) and listening port (example: 30305):
With the member node running, it is possible to check that it is connected to the bootstrap node or any other node in the network by attaching a console and running admin.peers. It may take up to a few seconds for the nodes to get connected.
Running A Signer (Clique)
To set up ETN-SC for signing blocks in Clique, a signer account must be available. The account must already be available as a keyfile in the keystore. To use it for signing blocks, it must be unlocked. The following command, for address 0x7df9a875a174b3bc565e6424a0050ebc1b2d1d82 will prompt for the account password, then start signing blocks:
Mining can be further configured by changing the default gas limit blocks converge to (with --miner.gastarget) and the price transactions are accepted at (with --miner.gasprice).
Running A Miner (Ethash)
For PoW in a simple private network, a single CPU miner instance is enough to create a stable stream of blocks at regular intervals. To start a ETN-SC instance for mining, it can be run with all the usual flags plus the following to configure mining:
This will start mining bocks and transactions on a single CPU thread, crediting all block rewards to the account specified by --miner.etherbase.
End-to-end example
This section will run through the commands for setting up a simple private network of two nodes. Both nodes will run on the local machine using the same genesis block and network ID. The data directories for each node will be named node1 and node2.
Each node will have an associated account that will receive some ether at launch. The following command creates an account for Node 1:
This command returns a request for a password. Once a password has been provided the following information is returned to the terminal:
The keyfile and account password should be backed up securely. These steps can then be repeated for Node 2. These commands create keyfiles that are stored in the keystore directory in node1 and node2 data directories. In order to unlock the accounts later the passwords for each account should be saved to a text file in each node's data directory.
In each data directory save a copy of the following genesis.json to the top level project directory. The account addresses in the alloc field should be replaced with those created for each node in the previous step (without the leading 0x).
The nodes can now be set up using etn-sc init as follows:
This should be repeated for both nodes. The following will be returned to the terminal:
The next step is to configure a bootnode. This can be any node, but for this tutorial the developer tool bootnode will be used to quickly and easily configure a dedicated bootnode. First the bootnode requires a key, which can be created with the following command, which will save a key to boot.key:
This key can then be used to generate a bootnode as follows:
The choice of port passed to -addr is arbitrary, but public Electroneum networks use 30303, so this is best avoided. The bootnode command returns the following logs to the terminal, confirming that it is running:
The two nodes can now be started. Open separate terminals for each node, leaving the bootnode running in the original terminal. In each terminal, run the following command (replacing node1 with node2 where appropriate, and giving each node different --port and authrpc.port IDs). The account address and password file for node 1 must also be provided:
This will start the node using the bootnode as an entry point. Repeat the same command with the information appropriate to node 2. In each terminal, the following logs indicate success:
In the first terminal that is currently running the logs resembling the following will be displayed, showing the discovery process in action:
It is now possible to attach a Javascript console to either node to query the network properties:
Once the Javascript console is running, check that the node is connected to one other peer (node 2):
The details of this peer can also be queried and used to check that the peer really is Node 2:
This should return the following:
The account associated with Node 1 was supposed to be funded with some ETN at the chain genesis. This can be checked easily using eth.getBalance():
This account can then be unlocked and some ETN sent to Node 2, using the following commands:
The same steps can then be repeated to attach a console to Node 2.
Summary
This page explored the various options for configuring a local private network. A step by step guide showed how to set up and launch a private network, unlock the associated accounts, attach a console to check the network status and make some basic interactions.
Last updated