Real world is a bit different.. DNS Caching.. While DNS Round Robin is good enough to distribute loads, it isnt' a very good method for failover, even with a very short TTL. Many home routers, still insist on caching results for a long time, no matter what the TTL says, and of course Windows internal caching etc..
Should not confuse the issue.. call it a 'poor man's load balancer' if you will, but it more of a last line failover, and during the time it takes for DNS to retry, and find another active node, an AWFUL lot of disgruntled customers will be calling ;)
Also so interesting to see some resolvers that don't think of using the second record, if the first one is down..
On 2023-07-18 17:09, Gerald Galster wrote:
While I understand it takes effort to maintain the replication plugin, this is especially problematic for small active/active high-availability deployments. I guess there are lots of servers that use replication for just 50 or 100 mailboxes. Cloudstorage (like S3) would be overkill for these.
Even without active/active, it's super useful for the simple active/backup configuration which I use on my personal mail server
This depends heavily on individual usage. Coming from an active/active deployment it's a major step backwards though: usually two servers are running independently in geographically dispersed datacenters. High-availabilty is achieved by a simple DNS entry that returns two ip addresses, one from each datacenter. Under normal circumstances that gives you 50/50 loadbalancing without loadbalancers, without additional components that can fail. In case one datacenter goes down, and that happens to every datacenter at some time, the other datacenter takes over - automatically, without any configuration changes. Additionally mail user agents (Outlook, Thunderbird, ...) don't need special configuration. If one ip address is unrechable they connect to the other one obtained via DNS and users can quite seemlessly send and receive email again. After the outage ceased and the other datacenter is back online again, there is nothing to do. No configuration changes, no error prone manual synchronization or promoting passive to active - it just works and heals itself. Being used to a carefree setup like that you don't want to go back.
Of course there are other possibilities like nfs, glusterfs, gfs2, zfs snapshots, ceph, minio or dsync backup but they all have their own drawbacks. For small mailservers that want high availability dsync replication is quite the perfect solution.
setup (one colo box, one home server) and a small company mail server; as such I'm pretty sad to see it go. Still, it is up to OX where they want to put their resources.
Well, it seems the dsync replication function is still there, just the replication plugin that notifies what to replicate is deprectated. Of course it's OX's decision, I'm just hoping they were not aware how useful replication is in the before mentioned scenario.
Moreover I'm quite sure this kind of small-scale replication does not have any impact on customers upgrading to the new cloud architecture. Big customers will go for cloud because it scales way better and does not have replication induced performance penalties and small customers probably can't afford to upgrade because it's too pricey.
I guess losing repl probably doesn't affect larger ISP type setups so much; it seems a bit more common to use shared storage (e.g. maildirs on an nfs appliance or similar) in those cases if they're actually running their own storage.
Do you provide dovecot pro subscriptions for such small deployments?
Unless I misunderstood the message (and I don't think I did), repl was removed in pro too. (I don't expect that pro is available on my usual choice of OS anyway..).
As I understood it dsync is still working. Replication configured via ssh is calling dsync under the hood, so if local storage and index/log formats don't change for single deployments, it seems to be more of a political decision. I know maintenance is not for free, that's why I suggested to think about a dovecot small/medium business edition with a more affordable price tag.
Best regards, Gerald
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