Re: Changing how LedgerSMB is run and it's installation is secured

On Sat, Mar 26, 2016 at 6:44 AM, David G <..hidden..> wrote:

Hi Michael,

At the moment I don't believe we support having multiple LedgerSMB
servers accessing the same company database, which is roughly what you
are referring to.

Multiple ledgersmb servers can access the same company database with no problem. There isn't really a difference between multiple service processes and multiple servers from the database perspective. It *is* possible to configure LedgerSMB to allow different versions of LedgerSMB to access the same database, but this isn't recommended for any extended period (it is designed for 0-downtime upgrades where worker processes might be recycled after the db upgrade is complete).

Having said that, I also don't think it would take too much in the way
of changes to make that possible (most state and consistency is in the
database already)

But Be Warned, it may not be possible before the last of the legacy code
has been rewritten.
Also there would need to be a fair investment in testing before you
would say it's production ready.

I think the only think one would note would be that some of our caching improvements are server-local. I think there are actually some 1.3 users who use multiple web servers against the same db server.

Chris and Erik may well contradict me on this, as they should if I'm
incorrect.

It's certainly a direction I'd like to be able to move towards,
especially if a robust and reliable bidirectional postgres replication
solution could be used (which it can't at the moment. a) it doesn't
exist. b) there are challenges that would need solving within our code
to do with data integrity eg: assignment of unique consecutive invoice
numbers across multiple DB backends)

I think it is impossible to guarantee unique consecutive invoice numbers across multiple db backends if you want to handle databases being off-line (this is a CAP problem). One possibility would be for each location to have its own series of unique consecutive invoice numbers......

As for bidirectional postgresql replication solutions, there are several including Bucardo and Postgres-bdr which provide different solutions to these problems, but they are not perfect and setting up something like this is rather advanced territory right now (at present we are not even sure what local requirements regarding things like invoice numbers are for such a solution).

Regardless of that use case, it solves some current issues running under
apache directly, and provides performance gains due to the way Starman
handles perl processes, and nginx as a reverse proxy caches static content

Oh, just a note, We are not proposing to prevent LedgerSMB from being
directly served by Apache etc. just making the primary method (ie: the
way it gets installed) be to run via Starman and a reverse proxy

Ok that is worth noting, and we *do* need better tooling in this corner.

Regards
David G

On 26/03/16 02:56, Michael Richardson wrote:
> > 1 Only ever run LedgerSMB using Starman (High-performance
> > preforking PSGI/Plack web server)
> > 2 Only ever bind Starman to localhost
>
> I'll all for this.
>
> (In bigger installations, one binds starman to a backend network, and uses
> nginx or apache or maybe varnish to spread load. Is there any local state in
> LedgerSMB that would prevent this...?)
>
> --
> ] Never tell me the odds! | ipv6 mesh networks [
> ] Michael Richardson, Sandelman Software Works | network architect [
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Best Wishes,

Chris Travers

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