The purpose of this hiring exercise is to test out your level in Elixir/OTP and see if you are a real problem solver which is one of Zenaton core values.
- All code is in
gitrepo (candidate can use his/her own github account). - OTP application is a mix project
- Engine application name is
:zenaton_engine(main Elixir module isZenatonEngine). - Agent application name is
:zenaton_agent(main Elixir module isZenatonAgent) - Agent Interface is just set of public functions of
ZenatonAgent(no API endpoint, no REST/SOAP ) - Applications should not use any database / disc storage. All needed data should be stored only in application memory.
- Candidate can use any Elixir or Erlang library he/she wants to.(but app can be written in pure Elixir/ Erlang/ OTP)
- Code accuracy also matters. Readable, safe, refactorable code is plus.
- Test implementation is plus.
The hearbeat is a feature implemented between one engine and n agents. It is made to improve monitoring, resiliency to any network or infrastructure issues.
The main work is that agents send a state, with additional information periodically and the engine answers back with an action and data.
You are free to choose the connection protocol to make this possible (HTTP/TCP/Erlang message).
Possible state for an agent:
- Starting: transient state between command listen and listening
- Stopping: transient state between command unlisten and disconnection
- Listening: connected to queues
- Sleeping: disconnected from queues
WARNING: You don't have to work on the queues connection, it is not the purpose of this exercise.
the Engine MUST stores agents identificator in memory with his current state and details.
the Engine MUST stores HEART_BEAT_PERIOD in memory which can be changed via Ex shell (value in sec).
the Engine MUST also have a messages_in_adhoc Map. Eg. messages_in_adhoc: %{"agent_1" => 3} where 3 represents the number of message available for agents which can be also changed.
When Engine receives:
state === starting
Then: action=listen with heart_beat_period
When Engine receives:
state === sleeping AND messages_in_adhoc related to the agent id > 0
Then: action=listen with heart_beat_period and the messages_in_adhoc related to the agent id = 0
When Engine receives:
state === listening AND agent not active for more than HEART_BEAT_PERIOD related to the agent id
Then: action=sleep
When Engine receives:
state === stopping
Then: delete the related agent_id in memory
update_heart_beat_period\1increment_messages_in_adhoc\1
It should be possible to open n Agent Application. Like in Zenaton.
When: Agent is asked to listen Then: state=starting, Send heartbeat
When: User is running active\0 method Then: if the Agent is state=listening it sends a fake message to Engine, the Engine must reset the sleeping_timer for this agent_identificator. If the Agent is in state=sleeping, it will make a listen (☝️), then do the same behaviour than when state=listening. If the agent is in state=stopping, it must do nothing.
When: Agent is asked to stop Then: state=stopping, Send heartbeat, log kill message
When: Send heartbeat Then: cancel previous timer if any, plan timer to send a new heartbeat in heart_beat_period, if < 3 calls in previous heart_beat_period => contact the engine with state, identificator, RAM. It should receive a response from the engine instantly
When: receiving action=Sleep Entering sleeping mode Then: state=sleeping, send heartbeat
When: receiving action=listen Entering listening mode Then: state=listening, send heartbeat
listen\0active\0stop\0
If you have some questions do not hesitate to open an issue on the repo 😬