circle.yml

dependencies:
  pre:
    - source /etc/lsb-release && echo "deb http://download.rethinkdb.com/apt $DISTRIB_CODENAME main" | sudo tee /etc/apt/sources.list.d/rethinkdb.list
    - wget -qO- http://download.rethinkdb.com/apt/pubkey.gpg | sudo apt-key add -
    - sudo apt-get update
    - sudo apt-get install rethinkdb=1.16.3~0precise
    - sudo cp /etc/rethinkdb/default.conf.sample /etc/rethinkdb/instances.d/instance1.conf
    - sudo /etc/init.d/rethinkdb restart

this is fixed to 1.16.3, it's pretty old. If you want to get the latests version just remove the version from the install command, like this:

    - sudo apt-get install rethinkdb