The problem is that my application is running on AWS which apparently doesn't support multicasting so I can't use Tomcat's DeltaManager. I thought of using one of the Store implementations for PersistentManager but that has the issues which I mentioned earlier. My aim is to get to the point where I can add or take away servers from the cluster without impacting user experience. Ideally all state would be stored in a central location (e.g. Redis). But, since this is difficult because of the way the application is built I thought of using one server and only persisting the sessions when the server goes down. But I still have to solve the issues I mentioned.
On Tue, May 12, 2020 at 6:06 PM Christopher Schultz < ch...@christopherschultz.net> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > Jonathan, > > On 5/12/20 05:51, Jonathan Yom-Tov wrote: > > I have an application which changes the state of user sessions in > > lots of places in the code. Is it possible to do a seamless switch > > of Tomcat servers, preserving all sessions? > > > > I know I can use PersistentManager to persist sessions and load > > them. I can think of two strategies: > > > > 1. Persist sessions periodically. This is more robust as I might > > not have control of when the server shuts down. 2. Persist sessions > > on server shutdown. > > > > > > The problem with the first approach is that I might lose the latest > > changes when the new server comes up. The problem with the second > > is that I'll have to lock access to the session until the old > > server is done saving it, which may make response times very slow. > > > > Is there a good solution to this that I might have overlooked? > > If you want to solve these problems: > > 1. Seamless (uninterrupted) restarts > 2. Always up-to-date (well, as much as possible) > 3. No downtime > > Then you really need a cluster where the sessions are being replicated > around the cluster. > > This will solve some other problems as well: > > 4. Expected downtime (e.g. OS/Tomcat/application upgrade) > 5. Unexpected downtime (network outage, hardware fault) > 6. Scaling-out (either manually or automatically) > > You can do it with as little as two Tomcat instances. If you only care > about being able to restart your application (and not the whole > server, for example), then you can even run them side-by-side on the > same server. You won't get protection against OS upgrades and > unexpected downtime in that case, but you can get familiar with the > setup without a whole lot of infrastructure. > > - -chris > -----BEGIN PGP SIGNATURE----- > Comment: Using GnuPG with Thunderbird - https://www.enigmail.net/ > > iQIzBAEBCAAdFiEEMmKgYcQvxMe7tcJcHPApP6U8pFgFAl66rKgACgkQHPApP6U8 > pFjsChAAtKdo2Ow+X+Lb0JQLAOxijryxlsRtO3rvdRPJLUxVG4ttVGXuJ86cPX9g > uRoyOrtgSw3N7mPMgL51B39Sp8GtB6zcjAiB4CQzOTXA3FiRN99Jna6dEVpCUcQx > xAUBNuJh6Q5N/l1tpLYIMgKXEmhGcexplNTEVl8IAb5tppNy1LtjUVMG3C4NolI1 > eKUVqNhtSmclBH9aDC94jlWLVH+OiKJhAfc965oCRv4E3vIcj5HGoKfK65iqFYPx > hzOMUzvJfsHBfNMo0UyKvRiDIFyBUgeUEIAJZWAJojhTSHymYpQozYBDIjCfNHYa > II6NYhYb9OuiwV9PEXFN2yZejBsgJvZzlbooWOg2z4nMmCItaTiUhOMyKNIY5wlz > iXnh85yx/GMRSsiQrTD6X4cAwCsXusHwoF/WC0JncYr7hZw/mqwcXDnMhUAccOCc > Z1l2x53yoVSH+RyoGgdG/DSWqLHZfiK/xr8UOtRbMD1WNfGOPo+GhpJBiSNSBeeS > LMNiQbvZEcTKOsxUFgUDPwB62kbDyLnt765tgrSOWubBIaHXBctTNLtv9sjp6ARG > DnNTmAtdk89UuhDA63iimDxx9jxDKsWKPz8Srf6RS7z8yUrlvFkfKQcIEaqHSLTr > LnbrTHK2k92bJonJua5hDcuTgU7axEBlWmXxChyZWmYm2r1R76M= > =suSa > -----END PGP SIGNATURE----- > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org > For additional commands, e-mail: users-h...@tomcat.apache.org > > -- [image: SysAid Technologies] <http://www.sysaid.com/?utm_source=signature&utm_medium=email&utm_campaign=sysaid-logo> Jonathan Yom-Tov Senior Architect jonathan.yom...@sysaid.com Phone (IL): +972 (3) 533-3675 Ext. 932 [image: SysAid Technologies] <https://www.sysaid.com/?utm_source=signature&utm_medium=email&utm_campaign=sysaid-logo-icon> [image: SysAid on Facebook] <https://www.facebook.com/SysAidIT> [image: SysAid on Twitter] <https://twitter.com/sysaid> [image: SysAid on Linked-in] <https://www.linkedin.com/company/sysaid-technologies-ltd> [image: SysAid on YouTube] <https://www.youtube.com/user/SysAidIT> [image: SysAid on Instagram] <https://www.instagram.com/sysaid_technologies/> [image: Banner] <https://www.sysaid.com/sig-link>
