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spec Put a transaction block around truncations Nov 14, 2017
.env Give the project a port that's not 5000 Nov 1, 2017
Gemfile Add simulator process Oct 7, 2017
Procfile Add reaper process Oct 7, 2017

rocket-rides-atomic Build Status

This is a project based on the original Rocket Rides repository to demonstrate what it might look like to implement idempotency keys in the same vein as Stripe's. See the associated article for full details.

The work done API service is separated into atomic phases, and as the name suggests, all the work done during the phase is guaranteed to be atomic. Midway through each API request a call is made out to Stripe's API which can't be rolled back if it fails, so if it does we rely on clients re-issuing the API request with the same Idempotency-Key header until its results are definitive. After any request is considered to be complete, the results are stored on the idempotency key relation and returned for any future requests that use the same key.


If you look in Procfile, you'll see these processes:

  • api: The main Rocket Rides API. It responds to requests and makes them idempotent using a required Idempotency-Key header.
  • completer: Finds failed API requests and attempts to push them through to completion (after a grace period to give the user a change to do it first).
  • enqueuer: Moves transactionally-staged jobs out of the database and over into a real job queue to be worked.
  • reaper: Reaps idempotency keys after some extended period wherein failed API requests would have been retried by a client or the completer a number of times already.
  • simulator: Randomly issues requests that will either succeed or fail to simulate traffic against api and give completer and enqueuer a chance to do something.

After you run forego start you should see the simulator issuing jobs against api right away. Some of these will succeed with a 201, and that will give the enqueuer something to do. Some will fail with a 500 as the simulator simulates some level of failure.

If you leave the programs running long enough, the completer will kick in and start to finish up any of the simulator's failed API requests. It only starts completing jobs that are at least five minutes old to give the original client a chance to retry them first.

If you leave the programs running really long, the reaper will kick in and start removing keys that are at least 72 hours old.



  1. Postgres (brew install postgres)
  2. Ruby (brew install ruby)
  3. forego (brew install forego)

Install dependencies, create a database and schema, and start running the processes:

bundle install
createdb rocket-rides-atomic
psql rocket-rides-atomic < schema.sql
forego run ruby up.rb
forego start

After those are running, from another terminal you should be able to create a ride:

curl -i -X POST http://localhost:5000/rides -H "Authorization:" -H "Idempotency-Key: $(openssl rand -hex 32)" -d "origin_lat=0.0" -d "origin_lon=0.0" -d "target_lat=0.0" -d "target_lon=0.0"

Or with a non-random idempotency key:

export IDEMPOTENCY_KEY=$(openssl rand -hex 32)
curl -i -X POST http://localhost:5000/rides -H "Authorization:" -H "Idempotency-Key: $IDEMPOTENCY_KEY" -d "origin_lat=0.0" -d "origin_lon=0.0" -d "target_lat=0.0" -d "target_lon=0.0"

Development & testing

Install dependencies, create a test database and schema, and then run the test suite:

bundle install
createdb rocket-rides-atomic-test
psql rocket-rides-atomic-test < schema.sql
bundle exec rspec spec/