CircleCI 2.0 - exit code 127, bundle command not found - ruby-on-rails

Question

I'm trying to get a rails app to run on Circle CI. With the following configuration I can't seem to get anything to work at all. When I ssh in, I can't even run sudo.
Here's the error output:
install dependencies
$ #!/bin/bash -eo pipefail
bundler install --jobs=4 --retry=3 --path vendor/bundle
/bin/bash: bundler: command not found
Exited with code 127
I noticed there is nothing but assets/ under the vendor directory.
Here's my configuration file:
version: 2
jobs:
build:
working_directory: ~/repo
docker:
- image: circleci/postgres:9.6-alpine-postgis-ram
- image: circleci/ruby:2.3
environment:
PGHOST: 127.0.0.1
PGUSER: staging
RAILS_ENV: test
- image: circleci/postgres:10.5
environment:
POSTGRES_USER: staging
POSTGRES_DB: test
POSTGRES_PASSWORD: ""
steps:
- checkout
# Download and cache dependencies
- restore_cache:
keys:
- v1-dependencies-{{ checksum "Gemfile.lock" }}
# fallback to using the latest cache if no exact match is found
- v1-dependencies-
- run:
name: install dependencies
command: |
bundle install --jobs=4 --retry=3 --path vendor/bundle
- save_cache:
paths:
- ./vendor/bundle
key: v1-dependencies-{{ checksum "Gemfile.lock" }}
# Database setup
- run: bundle exec rake db:create
- run: bundle exec rake db:schema:load
# run tests!
- run:
name: run tests
command: |
mkdir /tmp/test-results
TEST_FILES="$(circleci tests glob "spec/**/*_spec.rb" | circleci tests split --split-by=timings)"
bundle exec rspec --format progress \
--format RspecJunitFormatter \
--out /tmp/test-results/rspec.xml \
--format progress \
$TEST_FILES
# collect reports
- store_test_results:
path: /tmp/test-results
- store_artifacts:
path: /tmp/test-results
destination: test-results
All help is appreciated, thanks!

Answer 1

Your commands are running on the postgres container because it is listed first. If you make the ruby container first, then you will have access to bundle. And then when you SSH, you will be inside of the ruby container.
https://circleci.com/docs/2.0/configuration-reference/#docker--machine--macosexecutor
The first image listed in the file defines the primary container image where all steps will run.