On Tue, Dec 5, 2017 at 4:16 AM, Sami Ketola <sami.ketola at dovecot.fi> wrote:> On Mon, Dec 4, 2017 at 9:16 AM, Sami Ketola <sami.ketola at dovecot.fi> > wrote: > >> >> With every other tool you will face end users needing to invalidate >> their local caches and >> redownloading all headers if not also all mail bodies. >> >> Sami >> >> > On 4 Dec 2017, at 19.59, Webert de Souza Lima <webert.boss at gmail.com> > wrote: > > > > I don't think so. Been using imapsync for large scale migrations from > > external servers to our dovecot setup. Users don't even see it when the > key > > is switched (DNS changes). > > Go for it. > > You are wrong. There is no way to assign IMAP UID:s over IMAP protocol. It > simply does not support it. > With imapsync there is absolutely no way to preserve them and you will > face problems with IMAP UID:s > not matching the cached mail anymore. > > Trust us. We have run multiple migrations at scale of 10+ million users. > > SamiSorry, I might be wrong about cache invalidation, indeed. What I'm sure is that users will hardly notice any server change. We've never had user complaints about mailboxes resyncing or anything like that after imapsync'ing to a new server, that's why I'd recommend using imapsync with no worries. It's easy enough to test this on a single user account first and see how is imap client's behavior after the DNS change. Regards, Webert Lima DevOps Engineer at MAV Tecnologia *Belo Horizonte - Brasil*
> On 5 Dec 2017, at 12.46, Webert de Souza Lima <webert.boss at gmail.com> wrote: > > Sorry, I might be wrong about cache invalidation, indeed. What I'm sure is > that users will hardly notice any server change. > We've never had user complaints about mailboxes resyncing or anything like > that after imapsync'ing to a new server, that's why I'd recommend using > imapsync with no worries. > > It's easy enough to test this on a single user account first and see how is > imap client's behavior after the DNS change. >Can't really do DNS change to test with one user as DNS change affects all users. What we usually do is put layer of dovecot proxies in front of the legacy and destination platform and then have database with information if user has been migrated already and forward the connection to legacy or dovecot platform based on that info. That enables us to migrate user-by-user. And both users and mail server admins do notice if there is IMAP UID or POP3 UIDL changes. Imagine what happens when millions of users suddenly start to redownload terabytes of data. Sami
On Tue, Dec 5, 2017 at 8:54 AM, Sami Ketola <sami.ketola at dovecot.fi> wrote:> > Can't really do DNS change to test with one user as DNS change affects all > users.Yes, of course. For test purposes one could justchange the system's host file and simulate a DNS change, after imapsync is complete I meant a simple test just to see what happens at the client size, to see what the user itself could notice. On Tue, Dec 5, 2017 at 8:54 AM, Sami Ketola <sami.ketola at dovecot.fi> wrote:> > What we usually do is put layer of dovecot proxies in front of the legacy > and destination platform and then have database > with information if user has been migrated already and forward the > connection to legacy or dovecot > platform based on that info. That enables us to migrate user-by-user.Cool, we do that too :D. We might have learned that from you even. In that way users can use our Webmail from day 1 when migration starts. On Tue, Dec 5, 2017 at 8:54 AM, Sami Ketola <sami.ketola at dovecot.fi> wrote:> > And both users and mail server admins do notice if there is IMAP UID or > POP3 UIDL changes. Imagine > what happens when millions of users suddenly start to redownload terabytes > of data. > > Sami >That would just kill my cluster. Happened once due to NFS sharing hang. Terrible day to be alive. Regards, Webert Lima DevOps Engineer at MAV Tecnologia *Belo Horizonte - Brasil*