Port Allocator

[ddimtirov]

• [x] Support block port reservation as well as allocating ports by binding to port zero and releasing
• [x] Support pluggable registry to support multi-classloader and multi-process use-cases
  • [x] hash-map
  • [x] System.properties
  • [x] Consul or Etcd
• [x] Support Bonjour/zeroconf/mdns
• [x] Support TCP and UDP

[ddimtirov]

After analysis, block port reservation is identified to be the main use-case, while the rest of the initial scope boils down to exposing the allocated ports, and controlling the process of allocation. We chose not to support non-block allocations (i.e. keeping track of where "bind to port 0" ended up.

• The entry point is the Ports class, which orchestrates block allocation.
• In order to expose the allocated ports through different discovery mechanisms, we provide Ports.Exporter extension point. This can also be used to probe an allocated port and fail early if not available.
• In order to control the block allocation strategy, we provide the Ports.Registrar extension point.

Registrars can also be exporters, but hey need to be registered for each hook separately. Both can implement AutoCloseable and will be notified appropriately when the Ports instance is closed.

[ddimtirov]

Bonjour/mDNS can be accomodated as custom registrars.

I can't think right now of generic way to support UDP network/port allocation. Ignoring this requirement - if it comes back later will raise another ticket.