Sniffing periodically

Connection pools that return true for SupportsReseeding can be configured to sniff periodically. In addition to sniffing on startup and sniffing on failures, sniffing periodically can benefit scenarios where clusters are often scaled horizontally during peak hours. An application might have a healthy view of a subset of the nodes, but without sniffing periodically, it will never find the nodes that have been added as part of horizontal scaling, to help out with load

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .MasterEligible(9202, 9203, 9204)
    .ClientCalls(r => r.SucceedAlways())
    .Sniff(s => s.SucceedAlways(VirtualClusterWith
        .Nodes(100)
        .MasterEligible(9202, 9203, 9204)
        .ClientCalls(r => r.SucceedAlways())
        .Sniff(ss => ss.SucceedAlways(VirtualClusterWith
            .Nodes(10)
            .MasterEligible(9202, 9203, 9204)
            .ClientCalls(r => r.SucceedAlways())
        ))
    ))
    .SniffingConnectionPool()
    .Settings(s => s
        .DisablePing()
        .SniffOnConnectionFault(false)
        .SniffOnStartup(false)
        .SniffLifeSpan(TimeSpan.FromMinutes(30))
    )
);

healthy cluster all nodes return healthy responses

audit = await audit.TraceCalls(
    new ClientCall { { HealthyResponse, 9200 } },
    new ClientCall { { HealthyResponse, 9201 } },
    new ClientCall { { HealthyResponse, 9202 } },
    new ClientCall { { HealthyResponse, 9203 } },
    new ClientCall { { HealthyResponse, 9204 } },
    new ClientCall { { HealthyResponse, 9205 } },
    new ClientCall { { HealthyResponse, 9206 } },
    new ClientCall { { HealthyResponse, 9207 } },
    new ClientCall { { HealthyResponse, 9208 } },
    new ClientCall { { HealthyResponse, 9209 } },
    new ClientCall {
        { HealthyResponse, 9200 },
        { pool => pool.Nodes.Count.Should().Be(10) }
    }
);

Now let’s forward the clock 31 minutes. Our sniff lifespan should now go stale and the first call should do a sniff, which discovers we’ve scaled up to 100 nodes!

audit.ChangeTime(d => d.AddMinutes(31));

audit = await audit.TraceCalls(
    new ClientCall {
        { SniffOnStaleCluster },
        { SniffSuccess, 9202 },
        { HealthyResponse, 9201 },
        { pool => pool.Nodes.Count.Should().Be(100) }
    }
);

If we move the clock forward again by another 31 minutes, we now discover that we’ve scaled back down to 10 nodes

audit.ChangeTime(d => d.AddMinutes(31));

audit = await audit.TraceCalls(
    new ClientCall {

        { SniffOnStaleCluster },
        { SniffSuccess, 9202 },
        { HealthyResponse, 9200 },
        { pool => pool.Nodes.Count.Should().Be(10) }
    }
);

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