We have implemented a Java servlet running on JBoss container that uses CometD long-polling. This has been implemented in a few organizations without any issue, but in a recent implementation there are functional issues which appear to be related to the network setup of this organization.
Specifically, around 5% of the time, the connect requests are getting back 402 errors:
{"id":"39","error":"402::Unknown client","successful":false,"advice":{"interval":0,"reconnect":"handshake"},"channel":"/meta/connect"}
Getting this organization to address network performance is a significant challenge, so we are looking at a way to tune the implementation to reduce these issues.
Which cometd configuration parameters can be updated to improve this? maxinterval, timeout, multiSessionInverval, etc?
Thank you!
The "402 unknown client" error is due to the fact that the server does not see /meta/connect heartbeat messages from the client and expires the correspondent session on the server. This is typically due to network issues.
Once the client network is restored, the client sends a /meta/connect heartbeat message but the server doesn't have the correspondent session, hence the 402.
The parameter that controls the server side expiration of sessions is maxInterval, documented here: https://docs.cometd.org/current/reference/#_java_server.
By default is 10 seconds. If you increase it, it means you are retaining in the server memory sessions for a longer time, so you need to take that into account.