Thank you for all of your help, very informative. Regarding your last answer, I will look at it in greater detail and let you know if I have questions (I am less familiar with some of the term you mention there).
On Fri, Feb 5, 2016 at 11:48 PM, Christopher Schultz < ch...@christopherschultz.net> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Yuval, > > On 2/4/16 3:14 AM, Yuval Schwartz wrote: > >> On Wed, Feb 3, 2016 at 11:15 PM, Christopher Schultz < > >> ch...@christopherschultz.net> wrote: > > > > ELB usually uses HTTP keepalive, so that might be part of the > > issue. > > > >> ELB has a feature called "connection draining" which keeps > >> connections open while the instance is de-registering (my > >> instance begins de-registering when I shutdown tomcat) for a set > >> period of time (default: 300 s). It is this connection that stays > >> open when tomcat shuts down that causes the WARNING message to > >> appear. If I disable connection draining then I stop seeing the > >> WARNING when I shutdown tomcat. > > That'll do it. > > So, if you had waited 5 minutes between removing your node from ELB > and shutting-down Tomcat, you'd find that there also no errors. > > >> However, "connection draining" seems like a nice feature. One > >> option to overcome this WARNING while still keeping connection > >> draining would be to first undeploy my application, then, after > >> the connection draining time period expires, shutdown tomcat > >> (tested this, doesn't throw the warning). > > > >> Do you have any other recommendations for how I might keep this > >> feature and adjust something else in my configuration? Any light > >> to shed on the matter? > > Wait 5 minutes? > > 5 minutes is quite a long time to drain the node. How long is the > average request? In production, we use ELB with 30-second draining. > > (Then again, we have a layer of stateless httpd instances in > between... when we drain our Tomcat nodes, we typically wait over an > hour.) > > I think this might come down to the lack of flexibility of ELB. > > The way we use ELB, we are balancing between a set of httpd instances > which are *all* proxying to the same set of back-end Tomcat nodes. So > the currently-enabled set of httpd instances is irrelevant to the > client: any httpd can get to any Tomcat. > > When we want to service an httpd instance, we remove it from the ELB > with a short draining period and reboot, upgrade, whatever. No > interruption to the Tomcat nodes. > > If we want to service a Tomcat node, we bring-down the node from > *httpd*, not from ELB. We are using mod_jk which allows you to put a > Tomcat node into a "disabled" state, which means existing users will > still be routed to the node that is "going down" but new users will go > to other nodes instead. Once the number of sessions on that node goes > to zero, we STOP the node in mod_jk (NO TRAFFIC AT ALL to the node) > and then service it. > > ELB lacks this two-phase removal feature that mod_jk has. That means, > when you remove a node from ELB, the countdown starts for your > users... if they don't log off from that node, they will lose their > sessions in T minus 5 minutes. If you are using sticky sessions with > no clustering (like we are), then those users are just out of luck > when the 5-minute timer runs out. > > If you want better behavior, you are going to need more complexity. > > /On the other hand/, if you *are* clustered and don't use (or need) > sticky sessions, then you can significantly reduce that user-draining > period to the maximum reasonable response time you expect to be able > to serve. If you have a super-fast entirely-clustered (or stateless) > service, set the drain time to 1 second. If you have requests that > routinely last 45 seconds, set the drain-time to more like 90 seconds. > 5 minutes doesn't seem like it makes any sense to be in any scenario, > though. > > Hope that helps, > - -chris > -----BEGIN PGP SIGNATURE----- > Comment: GPGTools - http://gpgtools.org > Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ > > iEYEARECAAYFAla1GMcACgkQ9CaO5/Lv0PBO+ACeJLP4z3DUfcUqVmG30w7sYSsN > 5ggAoLDU8DSnA1vjVppiN9QU11GFsfng > =RhN2 > -----END PGP SIGNATURE----- > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org > For additional commands, e-mail: users-h...@tomcat.apache.org > >
