poptape-auctioneer

Bidding microservice written in Erlang using Cowboy, RabbitMQ and ets.

This microservice is intended as a lightweight service for tracking bids on an auction and broadcast via RabbitMQ to all auction bidders. It uses the cowboy webserver and RabbitMQ as well as ets tables.

The Process:

Auction Owner:

The auction owner sends an http post to an endpoint of /auction/<auction_id> The post has the usual x-access-token JWT header as well as the following json fields:

lot_id
username
start_price

The microservice then creates an exchange on RabbitMQ of type 'fanout' with an id of lot_id. This type of exchange allows a pub/sub model to be used. The service also creates two queues; one with a name matching the lot_id and one matching the username. The lot_id queue is intended for an audit microservice to use and is saved to disk. The other queue is intended for use by the auction owner.

A Bidder:

Any bidders connect via a websocket to the cowboy webserver sending a JWT with the connection request. This is verified as valid by a call to the 'authy' authentication microservice and, if valid, the JWT is stored in an ets table. Any subsequent websocket data sent checks against ets first. This is to enable faster running of the microservice and avoids too many http calls or disk accesses. Any data sent must contain the x-access-token field with the JWT as the content of this field. If the websocket connection is lost then the ets table entry is deleted and any subsequent connections need to be reverified against the authenication service.

The bidder comes in on an URL endpoint of /auction/<auction_id>/<lot_id> and sends the data listed below in a Json format (as well as the x-access-token JWT) in the websocket body:

username
bid

The microservice creates a queue with the name of username (I think I need to change this to make each queue unique as a user can bid on more than one lot at a time - not sure if RabbitMQ allows queues with non-unique names). The queue is bound to the exchange with the name that corresponds to the lot_id. Any subsequent websocket data sent is published to the exchange and all subscribers receive the messages to their own websocket.

Currently we return a whole load of data but this will undoubtably be reduced in the future to the bare minimum.

Extra bits:

All queues and exchanges are on a RabbitMQ virtual host as set in the microservice config file. This virtual host needs to be created seperately via the Rabbit CLI or web interface. Due to websockets, by default, having a timeout of 60 secs I've instigated a timer that sends a 'ping' websocket frame back to the client/browser to keep the connection alive. Browsers automatically respond with a 'pong' websocket frame.

Cowboy docs recommend that cowboy only respond to pings and not send pings as too many timers on the webserver could be a bad thing. However there doesn't exist a facility in the current javascript implementation of websockets to send a websocket 'ping' frame direct from javascript. Javascript docs say send a ping from the server and the server docs say the opposite!

API routes

TBD

Notes:

• Very early pre-alpha. Works(ish). No data sanitization or much other checking.

TODO:

• Need to add a check that create has been called before or not. Currently store a value in ets to check for this but maybe better in dets. If stored in dets we will need to delete from there after auction end to avoid 2Gb limit on dets files.
• Make bidder queue name unique on username and lot_id.
• Add extra ets data for storing latest bid data (?)
• Add extra message queue so auctionhouse service can stay in sync with auctioneer. Make this queue save to disk in case of server fail (?)
• Sanitize the input data.
• Only currently designed for a traditional English style auction.
• Need to think about pulling messages into auctionhouse microservice.