Hello, I've been thinking about the best way to achieve load balancing and making my mail servers highly available. So far I believe I have 2 scenarios: Scenario1: This should allow any to lose any of the servers and clients still have access to their emails (although I am not sure how the indexes would react to this and sudden disconnection) - 2 Dovecot Proxy servers, using a virtual IP to where the clients will connect to from the WAN and LAN - 2 Dovecot+Postfix servers with local cache - 2 NFS servers and synced with dsync (mirror, 1 server writes to its own NFS and changes synced to the other via dsync) Scenario2: Pretty much as above on the back end. However, with this there is no way to load balance users. - 2 Dovecot+Postfix server with local cache - 2 NFS servers synced with dsync - Make use of DNS MX record priority to provide access to secondary email server Anyone care to comment? Thanks. <BR CLEAR="ALL"> <hr style="border: 1px solid #CCC;"> <p style="font-style:italic; font-size:8pt; font-family:verdana; color:gray;">This document and attachments may contain technical data controlled under the U.S. International Traffic in Arms Regulations (ITAR) or the Export Administration Regulations (EAR) and may not be exported to a Foreign Person, either in the U.S. or abroad, without the proper authorization by the U.S. Department of State or Department of Commerce, whichever is applicable. CONFIDENTIALITY NOTE: This electronic transmission, including all attachments, is directed in confidence solely to the person(s) to whom it is addressed, or an authorized recipient, and may not otherwise be distributed, copied or disclosed. The contents of the transmission may also be subject to intellectual property rights and such rights are expressly claimed and are not waived. If you have received this transmission in error, please notify the sender immediately by return electronic transmission and then immediately delete this transmission, including all attachments, without copying, distributing or disclosing same. The recipient should check this e-mail and any attachments for the presence of viruses. Houston Sigma Technologies L.P. accepts no liability for any damage caused by any virus transmitted by this e-mail.</p>
I am actually going through the first stages of implementing your Scenario1. There is small difference: there will also be 2*Postfix relays also on the Dovecot Proxies. This allows placing them in a DMZ such that the "real" Dovecot/Postfix servers are placed away from the WAN. After much arguing and thinking I decided to go with this option as the most basic and possibly the simplest way to achieve MY goals: 1. fault tolerance of the entire system such that a failure will not impact mail delivery/access. 2. distribute users on at least two Dovecot servers to help when peak times arrive. 3. Ability to expand easily if demand rises 4. No use of custom hardware 5. Both internal (LAN) users and "away from office" (WAN) users will "see" the same setup to ease configuration (mostly done by users these days) I should say that other more complicated setups like full blown clusters and distributed file systems have been rejected due to their complexity (and the fact we do not have experience with them). Our user base is around 3-4K of heavy users. Andreas On 29-05-2013 00:23, Romer Ventura wrote:> Hello, > > > > I've been thinking about the best way to achieve load balancing and > making > my mail servers highly available. So far I believe I have 2 > scenarios: > > Scenario1: This should allow any to lose any of the servers and > clients > still have access to their emails (although I am not sure how the > indexes > would react to this and sudden disconnection) > > - 2 Dovecot Proxy servers, using a virtual IP to where the > clients > will connect to from the WAN and LAN > > - 2 Dovecot+Postfix servers with local cache > > - 2 NFS servers and synced with dsync (mirror, 1 server > writes to > its own NFS and changes synced to the other via dsync) > > > > Scenario2: Pretty much as above on the back end. However, with this > there is > no way to load balance users. > > - 2 Dovecot+Postfix server with local cache > > - 2 NFS servers synced with dsync > > - Make use of DNS MX record priority to provide access to > secondary > email server > > > > > > Anyone care to comment? > > > > Thanks.
Romer Ventura schrieb:> Scenario1: This should allow any to lose any of the servers and clients > still have access to their emails (although I am not sure how the indexes > would react to this and sudden disconnection) > > - 2 Dovecot Proxy servers, using a virtual IP to where the clients > will connect to from the WAN and LAN > > - 2 Dovecot+Postfix servers with local cacheYour proxy won't reconnect a user to backend B if the backend A fails.
We tried one time software solution, not very reliable under load, we move to coyotepoint equalizer hardware load balancer, very good cost and excellent reliable On Wed, May 29, 2013 at 7:23 AM, Romer Ventura <rventura at h-st.com> wrote:> Hello, > > > > I've been thinking about the best way to achieve load balancing and making > my mail servers highly available. So far I believe I have 2 scenarios: > > Scenario1: This should allow any to lose any of the servers and clients > still have access to their emails (although I am not sure how the indexes > would react to this and sudden disconnection) > > - 2 Dovecot Proxy servers, using a virtual IP to where the clients > will connect to from the WAN and LAN > > - 2 Dovecot+Postfix servers with local cache > > - 2 NFS servers and synced with dsync (mirror, 1 server writes to > its own NFS and changes synced to the other via dsync) > > > > Scenario2: Pretty much as above on the back end. However, with this there > is > no way to load balance users. > > - 2 Dovecot+Postfix server with local cache > > - 2 NFS servers synced with dsync > > - Make use of DNS MX record priority to provide access to > secondary > email server > > > > > > Anyone care to comment? > > > > Thanks. > > > <BR CLEAR="ALL"> > <hr style="border: 1px solid #CCC;"> > <p style="font-style:italic; font-size:8pt; font-family:verdana; > color:gray;">This document and attachments may contain technical data > controlled under the U.S. International Traffic in Arms Regulations (ITAR) > or the Export Administration Regulations (EAR) and may not be exported to a > Foreign Person, either in the U.S. or abroad, without the proper > authorization by the U.S. Department of State or Department of Commerce, > whichever is applicable. > CONFIDENTIALITY NOTE: This electronic transmission, including all > attachments, is directed in confidence solely to the person(s) to whom it > is addressed, or an authorized recipient, and may not otherwise be > distributed, copied or disclosed. The contents of the transmission may also > be subject to intellectual property rights and such rights are expressly > claimed and are not waived. If you have received this transmission in > error, please notify the sender immediately by return electronic > transmission and then immediately delete this transmission, including all > attachments, without copying, distributing or disclosing same. The > recipient should check this e-mail and any attachments for the presence of > viruses. Houston Sigma Technologies L.P. accepts no liability for any > damage caused by any virus transmitted by this e-mail.</p> > >