Execution Client

Warning

This tool should be considered alpha software and comes with all of the caveats and disclaimers that one might expect with early stage software. Use at your own risk.

The easiest way to start executing calls is to use the Ethereum Alarm Clock Client.

Installation can be done with pip

$ pip install ethereum-alarm-clock-client

Once the package is installed, a new command line tool eth_alarm should be available.

Running the Scheduler

The execution scheduler is a process that monitors the alarm service for upcoming scheduled function calls and executes them at their target block.

The scheduler requires an unlocked ethereum client with the JSON-RPC server enabled to be running on localhost.

$ eth_alarm scheduler
BLOCKSAGE: INFO: 2015-12-23 15:31:26,920 > Starting block sage
BLOCKSAGE: INFO: 2015-12-23 15:31:38,143 > Heartbeat: block #328 : block_time: 1.90237202068
BLOCKSAGE: INFO: 2015-12-23 15:31:43,623 > Heartbeat: block #335 : block_time: 1.75782920308
SCHEDULER: INFO: 2015-12-23 15:31:56,415 Tracking call: 0xa4a1b0d99e5271dd236a7f2abe30f81bba67dd90
CALL-0XA4A1B0D99E5271DD236A7F2ABE30F81BBA67DD90: INFO: 2015-12-23 15:31:56,415 Sleeping until 377
BLOCKSAGE: INFO: 2015-12-23 15:31:58,326 > Heartbeat: block #340 : block_time: 1.89721174014
BLOCKSAGE: INFO: 2015-12-23 15:32:06,473 > Heartbeat: block #346 : block_time: 2.07706735856
BLOCKSAGE: INFO: 2015-12-23 15:32:12,427 > Heartbeat: block #352 : block_time: 1.78518210439
BLOCKSAGE: INFO: 2015-12-23 15:32:24,904 > Heartbeat: block #357 : block_time: 1.67715797869
BLOCKSAGE: INFO: 2015-12-23 15:32:32,134 > Heartbeat: block #363 : block_time: 2.02664816647
BLOCKSAGE: INFO: 2015-12-23 15:32:41,400 > Heartbeat: block #368 : block_time: 1.70622547582
BLOCKSAGE: INFO: 2015-12-23 15:32:48,291 > Heartbeat: block #373 : block_time: 1.59583837187
BLOCKSAGE: INFO: 2015-12-23 15:32:53,134 > Heartbeat: block #378 : block_time: 1.51536617309
CALL-0XA4A1B0D99E5271DD236A7F2ABE30F81BBA67DD90: INFO: 2015-12-23 15:32:55,419 Entering call loop
CALL-0XA4A1B0D99E5271DD236A7F2ABE30F81BBA67DD90: INFO: 2015-12-23 15:32:55,452 Attempting to execute call
CALL-0XA4A1B0D99E5271DD236A7F2ABE30F81BBA67DD90: INFO: 2015-12-23 15:32:59,473 Transaction accepted.
  • The process will log a heartbeat every 4 blocks (1 minute).
  • When an upcoming call is found that is unclaimed, the scheduler will claim the call. (more on this later)
  • When an upcoming scheduled call is found within the next 40 blocks it will print a notice that it is now tracking that call.
  • When the target block is imminent (2 blocks) a notice that it is entering the call loop is logged.

Call Claiming

The scheduling client will claim scheduled calls. The logic for claiming is roughly the following.

  • Let N be a number between 0 and 255 that represents the current location in the call’s claim window.
  • If the claim value at N is not at least enough to pay for the claiming transaction and N is less than 240 the call is ignored.
  • If the call is profitable at N or N is greater than 240, a random number x is generated between 0 and 255.
  • If x is less than N then the client will attempt to claim the call. Otherwise the call is ignored.

Call Execution

Once the call enters the call window the client will check whether the call is claimed.

  • If the call is claimed and the current coinbase is the claiming address then the client will attempt to execute the call.
  • If the call is claimed and the claiming address is not the current coinbase the client will wait until the call enters free-for-all mode.
  • If the call is unclaimed then the client will attempt to execute it.

Once the client has sent a transaction attempting to execute the call it will wait for the transaction receipt and no further attempts to execute the call will be made.

Checks

The client implements all of the following

  • Don’t claim cancelled calls
  • Don’t execute cancelled calls
  • Don’t execute calls that have already been executed.
  • Don’t execute calls that don’t have enough ether to pay for the transaction.

Other Things You Should Know

  • The script only logs that the transaction was accepted which is not the same as successfully executing the call. see issue 1

Running a server

The scheduler runs nicely on the smallest AWS EC2 instance size. The following steps should get an EC2 instance provisioned with the scheduler running.

1. Setup an EC2 Instance

  • Setup an EC2 instance running Ubuntu. The smallest instance size works fine.
  • Add an extra volume to store your blockchain data. 16GB should be sufficient for the near term future.
  • Optionally mark this volume to persist past termination of the instance so that you can reuse your blockchain data.
  • Make sure that the security policy leaves 30303 open to connections from the outside world.

2. Provision the Server

  • sudo apt-get update --fix-missing
  • sudo apt-get install -y supervisor
  • sudo apt-get install -y python-dev python build-essential libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev python-virtualenv

3. Mount the extra volume

The following comes from the AWS Documentation and will only work verbatim if your additional volume is /dev/xvdb.

  • sudo mkfs -t ext4 /dev/xvdb
  • sudo mkdir -p /data
  • sudo mount /dev/xvdb /data
  • sudo mkdir -p /data/ethereum
  • sudo chown ubuntu /data/ethereum

Modify /etc/fstab to look like the following. This ensures the extra volume will persist through restarts.

#/etc/fstab
LABEL=cloudimg-rootfs   /        ext4   defaults,discard        0 0
/dev/xvdb       /data   ext4    defaults,nofail        0       2

Run sudo mount -a If you don’t get any errors then you haven’t borked your etc/fstab

4. Install Geth

Install the go-ethereum client.

  • sudo apt-get install -y software-properties-common
  • sudo add-apt-repository -y ppa:ethereum/ethereum
  • sudo apt-get update
  • sudo apt-get install -y ethereum

5. Install the Alarm Client

Install the Alarm client.

  • mkdir -p ~/alarm-0.7.0
  • cd ~/alarm-0.7.0
  • virtualenv env && source env/bin/activate
  • pip install ethereum-alarm-clock-client

6. Configure Supervisord

Supervisord will be used to manage both geth and eth_alarm.

Put the following in /etc/supervisord/conf.d/geth.conf

[program:geth]
command=nice geth --datadir /data/ethereum --unlock 0 --password /home/ubuntu/geth_password --rpc --fast --shh
user=ubuntu
stdout_logfile=/var/log/supervisor/geth-stdout.log
stderr_logfile=/var/log/supervisor/geth-stderr.log

Put the following in /etc/supervisord/conf.d/scheduler-v7.conf

[program:scheduler-v7]
user=ubuntu
command=/home/ubuntu/alarm-0.7.0/env/bin/eth_alarm scheduler --client rpc
directory=/home/ubuntu/alarm-0.7.0/
environment=PATH="/home/ubuntu/alarm-0.7.0/env/bin"
stdout_logfile=/var/log/supervisor/scheduler-v7-stdout.log
stderr_logfile=/var/log/supervisor/scheduler-v7-stderr.log
autorestart=true
autostart=false

7. Generate geth account

Use the following command to generate an account. The --datadir argument is important, otherwise the generated account won’t be found by our geth process being run by supervisord.

  • $ geth --datadir /data/ethereum account new

Place the password for that account in /home/ubuntu/geth_password.

You will also need to send this account a few ether. Twice the maximum transaction cost should be sufficient.

8. Turn it on

Reload supervisord so that it finds the two new config files.

  • sudo supervisord reload

You’ll want to wait for geth to fully sync with the network before you start the scheduler-v6 process.

9. Monitoring

You can monitor these two processes with tail

  • tail -f /var/log/supervisor/geth*.log
  • tail -f /var/log/supervisor/scheduler-v6*.log