Ping on first usage

Pinging is enabled by default for the Static, Sniffing and Sticky connection pools. This means that the first time a node is used or resurrected, a ping is issued a with a small (configurable) timeout, allowing the client to fail and fallover to a healthy node much faster than attempting a request, that may be heavier than a ping.

Here’s an example with a cluster with two nodes where the second node fails on ping

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(2)
    .Ping(p => p.Succeeds(Always))
    .Ping(p => p.OnPort(9201).FailAlways())
    .ClientCalls(c=>c.SucceedAlways())
    .StaticConnectionPool()
    .AllDefaults()
);

When making the calls, the first call goes to 9200 which succeeds, and the 2nd call does a ping on 9201 because it’s used for the first time. The ping fails so we wrap over to node 9200 which we’ve already pinged.

Finally we assert that the connectionpool has one node that is marked as dead

await audit.TraceCalls(

    new ClientCall {
        { PingSuccess, 9200},
        { HealthyResponse, 9200},
        { pool =>
        {
            pool.Nodes.Where(n=>!n.IsAlive).Should().HaveCount(0);
        } }
    },
    new ClientCall {
        { PingFailure, 9201},
        { HealthyResponse, 9200},
        { pool =>  pool.Nodes.Where(n=>!n.IsAlive).Should().HaveCount(1) }
    }
);

A cluster with 4 nodes where the second and third pings fail

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(4)
    .Ping(p => p.SucceedAlways())
    .Ping(p => p.OnPort(9201).FailAlways())
    .Ping(p => p.OnPort(9202).FailAlways())
    .ClientCalls(c=>c.SucceedAlways())
    .StaticConnectionPool()
    .AllDefaults()
);

await audit.TraceCalls(
    new ClientCall {
        { PingSuccess, 9200}, 
        { HealthyResponse, 9200},
        { pool =>
            pool.Nodes.Where(n=>!n.IsAlive).Should().HaveCount(0)
        }
    },
    new ClientCall {
        { PingFailure, 9201}, 
        { PingFailure, 9202}, 
        { PingSuccess, 9203}, 
        { HealthyResponse, 9203},
        { pool =>
            pool.Nodes.Where(n=>!n.IsAlive).Should().HaveCount(2) 
        }
    }
);

	The first call goes to 9200, which succeeds
	The 2nd call does a ping on 9201 because its used for the first time. This fails
	So we ping 9202. This also fails
	We then ping 9203 because we haven’t used it before and it succeeds
	Finally, we assert that the connection pool has two nodes that are marked as dead

All nodes are pinged on first use, provided they are healthy

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(4)
    .Ping(p => p.SucceedAlways()) 
    .ClientCalls(c=>c.SucceedAlways())
    .StaticConnectionPool()
    .AllDefaults()
);

await audit.TraceCalls(
    new ClientCall { { PingSuccess, 9200}, { HealthyResponse, 9200} }, 
    new ClientCall { { PingSuccess, 9201}, { HealthyResponse, 9201} },
    new ClientCall { { PingSuccess, 9202}, { HealthyResponse, 9202} },
    new ClientCall { { PingSuccess, 9203}, { HealthyResponse, 9203} },
    new ClientCall { { HealthyResponse, 9200} },
    new ClientCall { { HealthyResponse, 9201} },
    new ClientCall { { HealthyResponse, 9202} },
    new ClientCall { { HealthyResponse, 9203} },
    new ClientCall { { HealthyResponse, 9200} }
);

	Pings on nodes always succeed
	A successful ping on each node

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