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Elasticsearch.Net and NEST: the .NET clients [2.x] » Client Concepts - Elasticsearch.Net » Sniffing on connection failure
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Sniffing on connection failureedit

Sniffing on connection is enabled by default when using a connection pool that allows reseeding. The only IConnectionPool we ship that allows this is the SniffingConnectionPool.

This can be very handy to force a refresh of the pools known healthy node by inspecting Elasticsearch itself. A sniff tries to get the nodes by asking each currently known node until one response.

Here we seed our connection with 5 known nodes 9200-9204 of which we think 9202, 9203, 9204 are master eligible nodes. Our virtualized cluster will throw once when doing a search on 9201. This should a sniff to be kicked off.

When the call fails on 9201 the sniff succeeds and returns a new cluster of healthy nodes this cluster only has 3 nodes and the known masters are 9200 and 9202 but a search on 9201 still fails once

After this second failure on 9201 another sniff will be returned a cluster that no longer fails but looks completely different (9210-9212) we should be able to handle this

var audit = new Auditor(() => Framework.Cluster
    .Nodes(5)
    .MasterEligible(9202, 9203, 9204)
    .ClientCalls(r => r.SucceedAlways())
    .ClientCalls(r => r.OnPort(9201).Fails(Once))
.Sniff(p => p.SucceedAlways(Framework.Cluster
        .Nodes(3)
        .MasterEligible(9200, 9202)
        .ClientCalls(r => r.OnPort(9201).Fails(Once))
.Sniff(s => s.SucceedAlways(Framework.Cluster
            .Nodes(3, 9210)
            .MasterEligible(9210, 9212)
            .ClientCalls(r => r.SucceedAlways())
            .Sniff(r => r.SucceedAlways())
        ))
    ))
    .SniffingConnectionPool()
    .Settings(s => s.DisablePing().SniffOnStartup(false))
);

We assert we do a sniff on our first known master node 9202

Our pool should now have three nodes

We assert we do a sniff on the first master node in our updated cluster

audit = await audit.TraceCalls(
new ClientCall {
        { HealthyResponse, 9200 },
        { pool =>  pool.Nodes.Count.Should().Be(5) }
    },
    new ClientCall {
        { BadResponse, 9201},
{ SniffOnFail },
        { SniffSuccess, 9202},
        { HealthyResponse, 9200},
{ pool =>  pool.Nodes.Count.Should().Be(3) }
    },
    new ClientCall {
        { BadResponse, 9201},
{ SniffOnFail },
        { SniffSuccess, 9200},
        { HealthyResponse, 9210},
        { pool =>  pool.Nodes.Count.Should().Be(3) }
    },
    new ClientCall { { HealthyResponse, 9211 } },
    new ClientCall { { HealthyResponse, 9212 } },
    new ClientCall { { HealthyResponse, 9210 } },
    new ClientCall { { HealthyResponse, 9211 } },
    new ClientCall { { HealthyResponse, 9212 } },
    new ClientCall { { HealthyResponse, 9210 } },
    new ClientCall { { HealthyResponse, 9211 } },
    new ClientCall { { HealthyResponse, 9212 } },
    new ClientCall { { HealthyResponse, 9210 } }
);

Here we set up our cluster exactly the same as the previous setup Only we enable pinging (default is true) and make the ping fail

var audit = new Auditor(() => Framework.Cluster
    .Nodes(5)
    .MasterEligible(9202, 9203, 9204)
    .Ping(r => r.OnPort(9201).Fails(Once))
    .Sniff(p => p.SucceedAlways(Framework.Cluster
        .Nodes(3)
        .MasterEligible(9200, 9202)
        .Ping(r => r.OnPort(9201).Fails(Once))
        .Sniff(s => s.SucceedAlways(Framework.Cluster
            .Nodes(3, 9210)
            .MasterEligible(9210, 9211)
            .Ping(r => r.SucceedAlways())
            .Sniff(r => r.SucceedAlways())
        ))
    ))
    .SniffingConnectionPool()
    .Settings(s => s.SniffOnStartup(false))
);

We assert we do a sniff on our first known master node 9202

Our pool should now have three nodes

We assert we do a sniff on the first master node in our updated cluster

9210 was already pinged after the sniff returned the new nodes

audit = await audit.TraceCalls(
    new ClientCall {
        { PingSuccess, 9200 },
        { HealthyResponse, 9200 },
        { pool =>  pool.Nodes.Count.Should().Be(5) }
    },
    new ClientCall {
        { PingFailure, 9201},
{ SniffOnFail },
        { SniffSuccess, 9202},
        { PingSuccess, 9200},
        { HealthyResponse, 9200},
{ pool =>  pool.Nodes.Count.Should().Be(3) }
    },
    new ClientCall {
        { PingFailure, 9201},
{ SniffOnFail },
        { SniffSuccess, 9200},
        { PingSuccess, 9210},
        { HealthyResponse, 9210},
        { pool =>  pool.Nodes.Count.Should().Be(3) }
    },
    new ClientCall { { PingSuccess, 9211 }, { HealthyResponse, 9211 } },
    new ClientCall { { PingSuccess, 9212 }, { HealthyResponse, 9212 } },
new ClientCall { { HealthyResponse, 9210 } },
    new ClientCall { { HealthyResponse, 9211 } },
    new ClientCall { { HealthyResponse, 9212 } },
    new ClientCall { { HealthyResponse, 9210 } }
);
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