Setup Ethereum private Blockchain and sync them

To setup a private ethereum blockchain in ubuntu .

You have to install ethereum first

``` sudo apt-get install software-properties-common

sudo add-apt-repository -y ppa:ethereum/ethereum

sudo apt-get update

sudo apt-get install ethereum

```

Then create a private network , To init the initial block of chain you run this command

``` geth --datadir "firstserver" init "CustomGenesis.json" ```

When you run this command it will generate a genesis hash which should be similar to all private ethereum network if you want them to synchronize. If they have different genesis hash then they will not synchronize

Here --datadir “datadir” means the directory which will store your initial block of chain and the block will store further chain in this directory .

And CustomGensis.json will contain this data

{

   "nonce": "0xlookatmeimanonce",

   "timestamp": "0x00",

   "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",

   "extraData": "0x00",

   "gasLimit": "0x08000000",

   "difficulty": "0x0400",

   "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",

   "coinbase": "0x3333333333333333333333333333333333333333",

   "alloc": {

“”:{

}

   }

}

When you run this command a folder will create with name “firstserver” which contain the inital blockchain . and then you can start the private block chain.

Then start a private blockchain by command

``` geth --datadir firstserver --networkid 1234 --rpcport 8000 --rpcaddr 127.0.0.1 --port 30303 --rpc --rpcapi="db,eth,net,web3,personal,web3"  --maxpeers 3 --nat=any --nodiscover --rpccorsdomain "*"  console ```

What this command does ?

--datadir define the folder of blockchain

--networkid define a network on which all node should connect “important” , if you create  multiple private blockchain all should have same network id . i will discuss it in detail later.

--port define for private blockchain.

--rpcport is the port on which the your webAPi will interact means if you are using web3.js you can connect to this port and access all detail by  api .

--rpcaddr is the ip address to which private blockchain is bind , if i want to connect to other blockchain then i need this otherwise it take by default 127.0.0.1 or localhost

--rpcapi define all api which are disclose to webAPi like web3.js or ethereumj , you can add more api as you want to access more data.

--maxpeers  define how many peer of ethereum private network that private chain can connect.

--nat value       NAT port mapping mechanism , i use any.

--nodiscover  is “important” , this is use for not to discover by public ethereum network.

----rpccorsdomain "*" allow cors origin domain.

You can understand more tags of geth from this , I have described which i think necessary.

https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options

Now you single private blockchain has been created.

You  can create connect to 127.0.0.1:8000 by ethereum webApi like WEB3.JS and ETHEREUMJ . I have used WEB3.JS so i recommend to use it . It is javascript api .

Now you have create a private blockchain you want to create multiple blockchain and synchronize then.

Create a new private blockchain follow above same steps to create another private blockchain

``` geth --datadir "secondserver" init "CustomGenesis.json" ```

Check It should have same genesis hash as the above and CustomGenesis.json should be same.

``` geth --datadir secondserver --networkid 1234 --rpcport 8001 --rpcaddr 127.0.0.1 --port 30304 --rpc --rpcapi="db,eth,net,web3,personal,web3"  --maxpeers 3 --nat=any --nodiscover --rpccorsdomain "*"  console ```

Now both the blockchain are created you need to connect both of them.

Type admin.nodeInfo in both node , this will give

```{

 enode: "enode://38b4bfee228ebfa5d48927da2320ec4054f19d4d85e0d348ac08bff855b51b44a9f2e858e89fd3abd1e2f27d668aed3fadc4f9a7248a3d97cdc3c6568f7247e3@[::]:30303?discport=0",

 id: "38b4bfee228ebfa5d48927da2320ec4054f19d4d85e0d348ac08bff855b51b44a9f2e858e89fd3abd1e2f27d668aed3fadc4f9a7248a3d97cdc3c6568f7247e3",

 ip: "::",

 listenAddr: "[::]:30303",

 name: "Geth/v1.4.18-stable/linux/go1.5.1",

 ports: {

   discovery: 0,

   listener: 30303

 },

 protocols: {

   eth: {

     difficulty: 72633354,

     genesis: "0xdf7b6336757c45a8891ebc017a9ce1d75eb850063ceb65e2b0bab8ddaaf8987a",

     head: "0xd7236bedc7fa4f2ccef26fd81dc2f5652656bbc3766bb135e31b515433b8ba9e",

     network: 1234

   }

 }

} ```

If you run for firstserver

Create a file static-nodes.json inside firstserver and secondserver folder and from above json copy ‘enode’

"enode://38b4bfee228ebfa5d48927da2320ec4054f19d4d85e0d348ac08bff855b51b44a9f2e858e89fd3abd1e2f27d668aed3fadc4f9a7248a3d97cdc3c6568f7247e3@[::]:30303?discport=0

And change [::] to the ip , I am running in localhost can use

"enode://38b4bfee228ebfa5d48927da2320ec4054f19d4d85e0d348ac08bff855b51b44a9f2e858e89fd3abd1e2f27d668aed3fadc4f9a7248a3d97cdc3c6568f7247e3@127.0.0.1:30303?discport=0”

This enode is of firstserver you can write it in static-node.json file to peers second server like this

[

"enode://38b4bfee228ebfa5d48927da2320ec4054f19d4d85e0d348ac08bff855b51b44a9f2e858e89fd3abd1e2f27d668aed3fadc4f9a7248a3d97cdc3c6568f7247e3@127.0.0.1:30303?discport=0”,

"enode://pubkey@ip:port",

........

]

You can add many enode  to connection by separating it by comma.

And them again run secondserver and run this command “admin.peers”  , you can see the a array in which peers detail are shown ,

And same you should do for firstserver , copy secondserver enode data and paste it in firstserver’s static-node.json file .

Then run “admin.peers” , you can see the array which second server detail .

Create a account in firstServer

personal.newAccount("mypasswd") , in console you can see a hash , If this is your first account this will we your coinbase too

Run secondserver by adding “etherbase”

``` geth --datadir secondserver --networkid 1234 --rpcport 8001 --rpcaddr 127.0.0.1 --port 30304 --rpc --rpcapi="db,eth,net,web3,personal,web3"  --maxpeers 3 --nat=any --etherbase=”hashByfirstserver” --nodiscover --rpccorsdomain "*"  console ```

Type eth.coinbase in both now you can see the coinbase is same for both

Now start mining by

miner.start(1)  1 is for one thread for mining.

Now you can see both server will synchronize with eachother

Run command  eth.getBalance(eth.coinbase).toNumber(); in both server the balance of both will increase and would we same.

THANKS