[libvirt PATCH] src: warn if client hits the max requests limit

[Daniel P. Berrangé]

Since they are simply normal RPC messages, the keep alive packets are
subject to the "max_client_requests" limit just like any API calls.

Thus, if a client hits the 'max_client_requests' limit and all the
pending API calls take a long time to complete, it may result in
keep-alives firing and dropping the client connection.

This has been seen by a number of users with the default value of
max_client_requests=5, by issuing 5 concurrent live migration
operations.

By printing a warning message when this happens, admins will be alerted
to the fact that their active clients are exceeding the default client
requests limit.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---

I'm a little wary of this change. If we use anything less than VIR_WARN
it is not going to be useful, as we need it visible by default. At the
same time though I'm concerned that this might expose very many
deployments using an unreasonably low max_client_requests value for
their workload. For example OpenStack deployment tools have often left
this on the default setting and have been known to exceed it with live
migration running concurrently.

One possible optimization would be to only issue this warning once per
connected client, so we don't spam repeatedly ?

 src/rpc/virnetserverclient.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/rpc/virnetserverclient.c b/src/rpc/virnetserverclient.c
index d57ca07167..0d82726194 100644
--- a/src/rpc/virnetserverclient.c
+++ b/src/rpc/virnetserverclient.c
@@ -1259,6 +1259,10 @@ static virNetMessage *virNetServerClientDispatchRead(virNetServerClient *client)
                 client->rx->buffer = g_new0(char, client->rx->bufferLength);
                 client->nrequests++;
             }
+        } else {
+            VIR_WARN("Client hit max requests limit %zd. This may result "
+                     "in keep-alive timeouts. Consider tuning the "
+                     "max_client_requests server parameter", client->nrequests);
         }
         virNetServerClientUpdateEvent(client);
 
-- 
2.37.2