GossNet.Discovery.Consul 0.10.0

GossNet.Discovery.Consul

Consul-based node discovery for GossNet.Protocol.

Ships separately so the core package stays free of the Consul client dependency.

Installation

dotnet add package GossNet.Discovery.Consul

Usage

Register each gossip node with Consul under a shared service name, then point discovery at it:

using GossNet.Discovery.Consul;
using GossNet.Protocol;

var consulOptions = new ConsulDiscoveryOptions
{
    ServiceName = "gossnet",
    Address = new Uri("http://consul.internal:8500"),
    PassingOnly = true
};

var configuration = new GossNetConfiguration
{
    Hostname = "10.0.0.1",
    Port = 9055,
    DiscoveryProviderFactory = cfg => new ConsulNodeDiscovery(cfg, consulOptions)
};

using var node = new GossNetNode<MyMessage>(configuration);
node.Start();

DiscoveryProviderFactory is used rather than DiscoveryProvider because the provider needs the node's own hostname and port to exclude itself from its own results — a node registered in Consul always appears in its own service query.

Watching

ConsulNodeDiscovery implements IWatchableNodeDiscovery using blocking queries, so a service registering or deregistering reaches a node in about a round trip rather than after CacheDuration.

Nothing needs enabling — GossNetNode.Start() subscribes automatically. If the watch fails, the node logs it and falls back to cached polling.

Each request carries the X-Consul-Index from the previous result and the agent holds it open until that index moves. Three rules make that correct, and each fails quietly rather than loudly when it is wrong:

• An index that goes backwards means Consul restarted or the table was re-indexed. It must be reset to zero to re-baseline, or the query blocks forever and no further change is ever seen.
• An index below one must be treated as one, or the next query is a non-blocking read and the watch becomes a hot loop.
• An unchanged index means the wait elapsed, not that anything changed, so nothing is published.

Because those are server behaviours, they are verified against a real Consul container in GossNet.Discovery.IntegrationTests rather than against a fake.

A custom IConsulHealthClient keeps working unchanged; it simply will not watch. Implement IWatchableConsulHealthClient as well to opt in.

Options

Discovery runs on the message path, so results are cached. If Consul cannot be reached, a NodeDiscoveryException is thrown rather than returning an empty neighbour list — an unreachable agent must never be mistaken for a network of one.

License

MIT. See LICENSE.