Restfully

Phoenix server for demonstrating Wombat.

Requirements

1. Elixir
2. Phoenix
3. Postgres

Starting

1. get dependencies - mix deps.get
2. compile - mix compile
3. create database - mix ecto.create
4. add Restfully tables - mix ecto.migrate
5. start server with node name - iex --name [email protected] --cookie cookie -S mix phoenix.server

Endpoints

Base URL: http://localhost:4000/

Action	Endpoint	Description
GET	/counters	list counters
POST	/counters	create new counter
GET	/counters/:id	retrieve counter
GET	/counters/:id/next	syncronhous increment counter and get new value
GET	/counters/:id/incr	asynchronous increment counter and get old value
PUT	/delay/http_millis/:value	delay for counters/:id/incr http request (default 100)
PUT	/delay/delay_millis/:value	delay for counters/:id/incr serialized counter (default 100)
GET	/ets/bomb	trigger too many ets tables alarm
GET	/ets/defuse	clear too many ets tables alarm state
GET	/process/bomb	trigger too many processes alarm
GET	/process/defuse	clear too many processes state
GET	/atom/bomb	trigger too many atoms alarm

Notes on Endpoints

/counters/:id/incr

GET on /counters/:id/incr is asynchronous. The http response is sent immediately. A message is cast to a gen_server to increment the counter. The http_millis delay is the number of milliseconds delay added before sending the http response. This is meant to simulate internal processing. The delay_millis delay is the number of milliseconds delay between handling each message processed by the gen_server. Each /counters/:id/incr GET sends 101 messages to the gen_server. The large number of messages allows the message queue to grow faster. Tune the delays and the number of clients to adjust the growth and consumption rate of the message queue.

/counters/:id/next

GET on /counters/:id/next is synchronous, That is, the http response is sent after the database is updated. Note that the default Postgres isolation rules to not serialize writes, so concurrent GETs on /counters/:id/next may overwrite one another. That is, 1000 GETs on /counters/:id/next using 4 clients may not result in the counter incremented by 1000. The delay_millis delay is the number of milliseconds taken to update the counter. This is meant to simulate processing time. GET on /counters/:id/next does not use the https_millis delay.

Create counter

curl --header "Content-Type: application/json" --data-raw '{"counter": {"name": "fifty", "count": 0}}' http://localhost:4000/counters

Demonstrating Long Message Queue Alarm

1. Use POST /counters to create a new counter.
2. Monitor message queue length (Process,Sum message queue length)
3. Use a benchmarking tool to GET /counters/:id/incr
4. Wait for the message queue length alarm

Speed up the queue drain rate by changing delay_millis:

curl -X PUT http://localhost:4000/delay/delay_millis/0