Create a PDU Gateway service

We are currently using a python module to abstract communicating with the PDUs.

This solves most issues, but comes with the following drawbacks:

• Hard to keep track of state changes (I would like to know how long a port has been OFF for)
• Periodic polling would lead to duplicated queries
• Make it hard to auto-detect PDUs through MDNS/Bonjour/avahi/...

Here is the proposed sequence diagram:

sequenceDiagram
    participant client as Client
    participant pdu_gateway as PDU<br/>Gateway
    participant pdu as APC PDU<br/>10.42.0.42
    autonumber

    note over client: Register a new PDU
    client->>+pdu_gateway: POST /v1/pdu/<br/>{ name: apc, driver: apc_masterswitch, config: { host: 10.42.0.42 }}
    pdu_gateway->>pdu: Query the list of ports, their states and statuses
    pdu_gateway->>-client: 201 Created

    note over client: List PDUs
    client->>+pdu_gateway: GET /v1/pdu/
    pdu_gateway->>-client: 200 Success<br/>[{name: apc, driver: apc_masterswitch, ports: [{label: Port 1, state=ON}, ...]]

    note over client: Periodic PDU polling
    pdu_gateway->>pdu: Query the list of ports, their states and statuses

    note over client: Check the state of a single port
    client->>+pdu_gateway: GET /v1/pdu/apc/ports/1/state
    pdu_gateway->>-client: 200 Success<br/>ON

    note over client: Set the state of a PDU port
    client->>+pdu_gateway: POST /v1/pdu/apc/ports/1/state<br/>OFF
    pdu_gateway->>-client: 200 Success<br/>OFF