On Fri, 2012-06-08 at 12:56 +0200, Jan Zelený wrote:
> Hi everybody,
> I'm sending some patches which implement the primary server support as I
> see it. It it based on comment #6 in the related ticket
>
https://fedorahosted.org/sssd/ticket/1128
>
>
> Patch #0001 basically adds the necessary support in failover code
> Patches #0002 - #0004 extend this support in each provider
> Patch #0005 documents the new concept in failover section in man pages
> Patches #0006 - #0008 add new options for each provider which utilize this
> concept.
>
>
> Just briefly about the approach. When adding a new server to the list of
> servers related to a service, each server can be marked either as primary
> or secondary.
>
> When selecting new server from failover list, the algorithm iterates over
> the list twice - first it tries to look for primary server and if none is
> found, it tries also secondary server.
>
> If a server is returned from failover, and it is not primary server, a
> timeout is set (currently hard-coded for 30 seconds) for primary server
> lookup. This timeout is rescheduled until a primary server is found. If a
> primary server (either working or neutral) is found after this timeout,
> status of the backend is reset, i.e. first all offline and then all
> online callbacks are called. This is done to interrupt connection to the
> secondary server in favor of new connection to a primary server.
I think this is dangerous. I don't want us to force offline operation
even momentarily.
I changed the concept to re-connection, which is done instantly, without
scheduling any events. Combined with the possibility to mark LDAP connections
as "disconnecting", it is addressing the original issue of going offline and
back online.
> I have just couple concerns about things which I have yet to
inspect.
> First of all when connection to the old server is interrupted, what if an
> operation is currently in progress on this connection? I know ticket
> #1027 induces similar scenario. Maybe to kill two birds with one stone I
> could design an extension to immediately invoke callbacks of all
> operations running on existing connection. What do you think about that?
Better behavior would be to allow existing communications to complete,
and only direct new requests to the primary server. I think interrupting
in-progress requests would be dangerous and unpredictable.
Done, see the proposed concept of reconnection.
> My second concern is about port status timeout. After some time
a port is
> marked as neutral if originally marked as not-working. That effectively
> leads to second attempt to primary server reconnection being successful
> even though the server is still not running. As a result, an unnecessary
> reconnection to secondary server is performed once some data are needed
> from the server.
This is intentional behavior. It's done so that if we eventually lose
connection to the current server, we'll be able to retry that one again
while looping through the failover code. I'd suggest just resetting the
port-neutralizer timeout when you make the primary reconnection attempt
and it fails.
I left it as it was. It is impossible for failover code to check if the port
is online. Therefore this solution is probably the best we can do.
> Thank you very much for your opinions on this
> Jan
General comment: I don't think I like the term "secondary" here. I think
we might want to use something more descriptive. Perhaps "backup"? I'm
soliciting suggestions :)
Backup seems as good as any. Should I rename all those config options or do you
have any other ideas?
Patch 0001: Nack
See above concerns.
Hopefully addressed.
Patch 0002: Nack
Please add a comment explaining why secondary_urls gets promoted to
primary.
Added DEBUG message, that's more useful I guess
Patch 0003: Ack
Patch 0004: Nack
Please add a comment explaining why secondary_urls gets promoted to
primary.
Added DEBUG message, that's more useful I guess
Patch 0005: Nack
Typos in manpage:
"For each failover-enabled config option two variants exists:" should be
"For each failover-enabled config option, two variants exist:"
and
"it will replace current" should be "it will replace the current"
Fixed
Patch 0006: Nack
Typo in the manpage:
"If neither options is specified," should be "If neither option is
specified,"
You removed the warning about missing ldap_uri. You should put it back
in if both urls and secondary_urls are NULL.
Please add the same config debug information that you used in the IPA
provider (about promoting secondary servers to primary)
Done
Patch 0007: Nack
Same comment about the warning when the servers are unspecified.
Done
Thanks
Jan