Hi Scott,
I thoroughly enjoyed the updated docs. It is just what I needed. I just want to mention a few inferences I have now from reading it.
Thanks.
In a load balanced setup using connect_timeout and prepost_timeout, this will protect me from sending either newly established connections (rare event due to persistence) as well as each and every individual request from being sent to a failed tomcat node based on CPING/CPONG messages. These messages only detect whether or not the container (I'm using tomcat) is healthy enough to respond to such a message but not necessarily anything more, correct? Basically, its ajp listener is responsive. Plus, if I need more high speed error detection I can use
That's correct.
reply_timeout. Sound correct?
That one, reply_timeout, is not really meant for high speed detection. Usually you've got an ap, that every now and then needs 10 or 20 seconds for an answer and you don't like to disable a worker automatically because of those rare events. So normally one sets reply_timeout to 1, 2 or 3 minutes.
Now with the new max_reply_timeouts one can experiment with lower values. It's new, so not enough experience for good suggestions.
I get confused on the recovery_options section. How does it work in a load balanced environment? If tomcat receives a request and processes some of it followed by a catastrophic failure before completing the response, what exactly does a repeated request from the client do? Assuming recovery_options is set to 0.
Value "0" means, if you don't get any part of the answer and an error occurs (network, reply_timeout, ...) then send the same request again to another member of the load balancer (if a working member is remaining).
That's why you usualy really want to not use value "0" in case your app has data changing use cases. Most apps have.
If you use REST principles and HEAD and GET is always idempotent for your app, the new (version 1.2.24) bits 8 and 16 are your friend!
Also, I get confused with the section describing the retries directive. In a load balanced environment, would the connector retry no matter the state (tcp state here) of the connection whether it be established already? Would it retry against the same backend tomcat server? The reason I ask is because the docs say "If the load balancer can not get a free connection for a member worker from the pool, it will try again a number of times given by retries." I highlighted the words that confuse me.
We have to strongly make a difference between retries of a non-lb worker and of a load balancer worker. A normal worker has a simple retry procedure, independant of the fact, if it is used directly or as part of an lb. If it detects an error it uses another pool connection and by default tries once more.
An lb has another idea of retries. It uses retries if all connections to a backend are busy. For Apache with default config, this should never happen, because we allow as many connections as threads per process. So any request should be able to get a connection without waiting (maybe it needs to start a new one). For the other web servers we don't have a good way to detect the "correct" pool size. In some cases even for Apache it might be interesting to use a smaler pool size, in case the backend is only used occasionally and/or you want to prevent it from getting flodded in case of congestion. Then you might run out of available connections and requests will have to wait. LB retries configure this waiting.
Every 60 seconds would we expect the connector to attempt to send a valid request to a backend tomcat and fail or once a worker goes into error state do we only check with CPING/CPONG requests during the maintenance cycle?
The maintenance uses a real request and handles it as if the backend wouldn't have failed. If you enabled CPing/CPong this means, that it would detect a still broken backend early and transparently send the request to another member. Because no part of the request (the CPing doesn't count) already has been send, the failover to another member happens independently of recovery_options (i.e. even with recovery_options 3).
If you like to improve the page about load balancing or the timeouts page, or you want to add some parts about retries and recovery: contributions are welcome.
Regards, Rainer --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
