Enable multi-pool client connections

[mostafa]

At the moment GatewayD supports a pair of connection pools for managing available and busy connections. On one hand, these pools enables many incoming client, limited by the capacity of the pools, to be connected to a single database server. On the other hand, each client connection is mapped to a single server connection. This works, but is not ideal.

The idea here is to let GatewayD connect to multiple databases at the same time per configuration group, aka. tenant. Each configuration group should have configuration for multiple clients, pools, proxies and a single server. Note that clients, pools and proxies have named groups, yet there will be a single server listening for all of these databases. The distributionStrategy and the splitStrategy config parameters of the server object will decide how the connection are routed to their corresponding database connections (clients).

This should eventually enable a range of possibilities including routing, switching and relaying, to name the least.

This is a possible task list:

• [ ] Add a named config group (for clients, pools, proxies and servers) to config package to load the following config example
• [ ] Connect to multiple databases based on the named client config groups
• [ ] Create multiple pools per named config group and add corresponding clients to each pool
• [ ] Create multiple proxies per named config group and connect them with each pool
• [ ] Create a single server and attach all proxies to it
• [ ] Add tests

This is what the global config might look like after this change, yet other ideas should be explored.

clients:
  default:
    active-writes: # <- This is the "named config group"
      network: tcp
      address: localhost:5432
      ...
    standby-reads:
      network: tcp
      address: localhost:5433
      ...

pools:
  default:
    active-writes:
      size: 10
    standby-reads:
      size: 10

proxies:
  default:
    active-writes:
      healthCheckPeriod: 60s
    standby-reads:
      healthCheckPeriod: 60s

servers:
  default:
    distributionStrategy: ab-testing, canary, write-read-split (?), round-robin, murmur-hash, etc.
    splitStrategy:
      active-writes: 90 # percent
      standby-reads: 10 # percent (automatically deduced)
    ...

Related

• #55

Resources

• Types of load balancing algorithms
• 10 Load Balancing Techniques: Mastering the Art of Distributed Computing