Jail to jail network performance?
rwatson at FreeBSD.org
Wed Sep 14 03:04:39 PDT 2005
On Wed, 14 Sep 2005, Lyndon Nerenberg wrote:
> On Sep 13, 2005, at 11:59 PM, Uwe Doering wrote:
>> Now, for security reasons jails normally are confined in separate
>> filesystems, or at least in separate parts of a common one. So in case
>> of MySQL you would have to use TCP sockets to communicate between
>> jails. This socket type typically consumes more CPU because of TCP's
>> protocol overhead. However, whether you would actually notice any
>> difference in speed basically depends on how much excess CPU power
>> there is available on that server.
> Ignoring security (or filesystem namespace issues) I will just note that
> using named sockets for local IPC is a Good Thing. When I worked at
> Messaging Direct I taught sendmail to speak LMTP over named sockets, and
> our local delivery rate (to our IMAP server) went up by a factor of 10.
> It would be really cool if we could figure out a way to do AF_UNIX
> between jails, but I confess to not having thought about any of the
> implications ... (Maybe netgraph can help here?)
There are several ways you can do it, but they generally fall into two
classes of activies:
(1) Modifying the name space exclusion assumption for jails, so that the
file system name spaces overlap. One way to do this is with nullfs.
(2) Having a daemon or tool that runs outside of the jail and brokers
communication between the jails. One example might be a daemon that
inserts a UNIX domain socket into both jails and then provides
references to shared IPC objects between the two "by request".
Another example might be a daemon or tool that responds to a request
and creates a hard link from a socket/fifo endpoint visible in one
jail to a name visible in another jail, perhaps when setting up the
jail. The former requires more infrastructure, but the latter is less
Robert N M Watson
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