[SSSD] [PATCHES] Primary server support in SSSD

Stephen Gallagher sgallagh at redhat.com
Thu Jul 19 20:10:08 UTC 2012


On Tue, 2012-07-17 at 11:21 +0200, Jan Zelený wrote:
> Dne středa 11 července 2012 13:34:33, Stephen Gallagher napsal(a):
> > On Thu, 2012-06-21 at 12:15 +0200, Jan Zelený wrote:
> > > > 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
> > 
> > These patches look good by inspection, but due to divergence in the
> > codebase, they no longer apply atop the master. Please rebase them so I
> > can run some tests.
> > 
> > Also, the AD provider probably needs modification as well to take
> > advantage of this new feature (sorry, it landed first).
> 
> Rebased on top of current master. Those AD provider changes are included as 
> well, I didn't have a chance to test them though.


These patches don't apply cleanly. Patch 0010 fails with missing blobs.
Please submit rebased patches (or identify which other patches are
required).
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