Why are builds failing with “Cannot find Elasticsearch launch script from [elasticsearch]”?

Build Environment
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1

I’ve followed these instructions to install Elasticsearch.

Within a Rails app I’m starting a Test::Cluster to use within rspec tests.

#rails_helper.rb
require 'elasticsearch/extensions/test/cluster'

config.before :all, elasticsearch: true do
  # Start elasticsearch cluster before test run
  Elasticsearch::Extensions::Test::Cluster.start(
    port: 9250,
    nodes: 1,
    timeout: 120
  ) unless Elasticsearch::Extensions::Test::Cluster.running?(on: 9250)
end

config.after :suite do
    # Stop elasticsearch cluster after test run
  Elasticsearch::Extensions::Test::Cluster.stop(port: 9250, nodes: 1) if Elasticsearch::Extensions::Test::Cluster.running?(on: 9250)
end

Everything works fine when testing locally, but when I push to CircleCI the build fails with

An error occurred in an `after(:suite)` hook.
Failure/Error: Elasticsearch::Extensions::Test::Cluster.stop(port: 9250, nodes: 1) if Elasticsearch::Extensions::Test::Cluster.running?(on: 9250)

Errno::ENOENT:
  No such file or directory - Cannot find Elasticsearch launch script from [elasticsearch] -- did you pass a correct path?

As far as I can tell, I am configuring the build correctly to use Elasticsearch

#circle.yml
machine:
  services:
    - elasticsearch

or

#circle.yml
dependencies:
  cache_directories:
    - elasticsearch-5.1.1 # relative to the build directory
  post:
    - if [[ ! -e elasticsearch-5.1.1 ]]; then wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-5.1.1.tar.gz && tar -xvf elasticsearch-5.1.1.tar.gz; fi
    - elasticsearch-5.1.1/bin/elasticsearch: {background: true}
    - sleep 10 && wget --waitretry=5 --retry-connrefused -v http://127.0.0.1:9200/

What is the correct way to install Elasticsearch on CicleCi?