Backing up an Amazon EBS volume with CoreOS

CoreOS is all the rage these days and I find myself having to reinvent a lot of patterns. At Justcoin we produce up to 7,500 new Bitcoin addresses for our customers every day. The key pool functionality of bitcoind (Bitcoin Core) keeps 10,000 unused addresses for future use. When you ask bitcoind to create a new address it actually comes out of this pool. We’re moving over to HD wallets for our customers soon which could be the subject of another post.

There are three steps to the backup routine:

  • Create a scheduled task/cron job for the daily backup
  • Produce a backup file of the bitcoin wallet
  • Instruct Amazon EC2 to create a snapshot

The timer

Timers in systemd are unit files with the .timer file extension. A service with the same unit name but with the .service extension is run when the timer elapses. We’ll create a timer called bitcoind-backup.timer:

I’m not sure if it’s strictly necessary to run the timer on the same CoreOS instance as the timer.

The wallet backup and the EBS snapshot

The backup service issues the bitcoind RPC command backupwallet, which “Safely copies wallet.dat to destination”. An EBS snapshot is initiated using AWS CLI after the backup is completed.

  • Line 8: Alex Crawford’s simple awscli Docker image allows management of AWS resources.
  • Line 9: My bitcoind Docker image lets us issue RPC commands from the bitcoind CLI
  • Line 15, 18: We run bitcoind using Docker. This link allows the backup instance (bitcoind-backup) to connect to the live hot wallet (bitcoind)
  • Line 25–26: We store our AWS key and secret in CoreOS’ etcd
  • Line 30: We also store the AWS volume id of the hot wallet’s data directory inside etcd

Getting everything up and running

fleetctl load bitcoind-backup.service
fleetctl load bitcoind-backup.timer
fleetctl start bitcoind-backup.timer


There’s a lot of extra typing involved to accomplish tasks using CoreOS and Docker. I’d still take it over Chef any day.

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This post is licensed under CC BY 4.0 by the author.