ConnectionBalancer Bug

[dmsqls]

Hi. Report a bug in ConnectionBalancer

When pickTargetHandler is called, Count 1 increases as shown below.

BalancedConnectionHandler&
ExactConnectionBalancerImpl::pickTargetHandler(BalancedConnectionHandler&) {
--- skip ---
    min_connection_handler->incNumConnections();             ///< increment connection count
  }

  return *min_connection_handler;
}

However, the connection count is always 0, and the connection balancer is not processed as expected. (See log below)

[DEBUG] WORKER[0] CONNECTION COUNT[0]
[DEBUG] WORKER[1] CONNECTION COUNT[0]
[DEBUG] incNumConnections!!!!!!            ///< increment count 1
[DEBUG] decNumConnections!!!!!!           ///< decrement ??
[DEBUG] incNumConnections!!!!!!           ///< increment count 1 ???
///< next connection receive
[DEBUG] WORKER[0] CONNECTION COUNT[0]      //< why 0???
[DEBUG] WORKER[1] CONNECTION COUNT[0]
[DEBUG] incNumConnections!!!!!!
[DEBUG] decNumConnections!!!!!!
[DEBUG] incNumConnections!!!!!!

Temporarily modified as follows and it resolved.

BalancedConnectionHandler&
ExactConnectionBalancerImpl::pickTargetHandler(BalancedConnectionHandler&) {
--- skip ---
    min_connection_handler->incNumConnections();
#ifdef _BUG_CONN_BALANCER_ 
    min_connection_handler->incNumConnections();            ///< add
#endif

  }

  return *min_connection_handler;
}

Please review.

Thanks.

Reference information

Envoy Binary Version
./envoy version: 430fb4cd4004831170885184066045a3902acc4b/1.17.0/Modified/RELEASE/BoringSSL

Configuration

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: test-filter
  namespace: istio-system
spec:
  configPatches:
  - applyTo: LISTENER
    match:
      context: SIDECAR_OUTBOUND
      listener: {}
    patch:
      operation: MERGE
      value:
        connection_balance_config:
          exact_balance: {}

[mattklein123]

cc @lambdai I think this is the bug you are currently fixing?

[dmsqls]

cc @lambdai I think this is the bug you are currently fixing

No, I'm not currently fixing it.

[lambdai]

@dmsqls Thanks for the analysis.
Will be fixed by #15842

Before the fix, only the balance depends on the connections owned by the virtualoutbound listener. The number of connections is usually 0 there.
With my fix and the envoy filer crd, the connection will be balanced as your expectation

[dmsqls]

Thank you. It works as expected. 👍