falling-over.asciidoc

Fail over

When using a connection pool with more than one node, a request will be retried if the call to a node throws an exception or returns a 502, 503 or 504 response.

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .ClientCalls(r => r.FailAlways())
    .ClientCalls(r => r.OnPort(9201).SucceedAlways())
    .StaticConnectionPool()
    .Settings(s => s.DisablePing())
);

audit = await audit.TraceCall(
    new ClientCall {
        { AuditEvent.BadResponse, 9200 },
        { AuditEvent.HealthyResponse, 9201 },
    }
);

502 Bad Gateway

Will be treated as an error that requires retrying.

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .ClientCalls(r => r.FailAlways(502))
    .ClientCalls(r => r.OnPort(9201).SucceedAlways())
    .StaticConnectionPool()
    .Settings(s => s.DisablePing())
);

audit = await audit.TraceCall(
    new ClientCall {
        { AuditEvent.BadResponse, 9200 },
        { AuditEvent.HealthyResponse, 9201 },
    }
);

503 Service Unavailable

Will be treated as an error that requires retrying.

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .ClientCalls(r => r.FailAlways(503))
    .ClientCalls(r => r.OnPort(9201).SucceedAlways())
    .StaticConnectionPool()
    .Settings(s => s.DisablePing())
);

audit = await audit.TraceCall(
    new ClientCall {
        { AuditEvent.BadResponse, 9200 },
        { AuditEvent.HealthyResponse, 9201 },
    }
);

504 Gateway Timeout

Will be treated as an error that requires retrying.

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .ClientCalls(r => r.FailAlways(504))
    .ClientCalls(r => r.OnPort(9201).SucceedAlways())
    .StaticConnectionPool()
    .Settings(s => s.DisablePing())
);

audit = await audit.TraceCall(
    new ClientCall {
        { AuditEvent.BadResponse, 9200 },
        { AuditEvent.HealthyResponse, 9201 },
    }
);

If a call returns a valid HTTP status code other than 502 or 503, the request won’t be retried.

Important

Different requests may have different status codes that are deemed valid. For example, a 404 Not Found response is a valid status code for an index exists request.

var audit = new Auditor(() => VirtualClusterWith
    .Nodes(10)
    .ClientCalls(r => r.FailAlways(418))
    .ClientCalls(r => r.OnPort(9201).SucceedAlways())
    .StaticConnectionPool()
    .Settings(s => s.DisablePing())
);

audit = await audit.TraceCall(
    new ClientCall {
        { AuditEvent.BadResponse, 9200 },
    }
);