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We will inevitably have people running old unicorn versions
for many years to come; but they may be reading the latest
documentation online.
Annotate when the new features (will) appear to avoid misleading
users on old versions.
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Any chrooting would need to happen inside Worker#user, because
you can't chroot until after you have parsed the list of groups,
and you must chroot before dropping root privileges.
chroot adds an extra layer of security, so that if the unicorn
process is exploited, file system access is limited to the chroot
directory instead of the entire file system.
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They'll continue to be maintained, but we're no longer advertising
them. Also, favor lowercase "unicorn" while we're at it since that
matches the executable and gem name to avoid unnecessary escaping
for RDoc.
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This has not been used since unicorn 4.0.0 over three years ago.
This is an incompatible change, but hopefully nobody uses this in
before_fork/after_fork hooks anywhere.
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Signaling using normal kill(2) is preserved, but the master now
prefers to signal workers using a pipe rather than kill(2).
Non-graceful signals (:TERM/:KILL) are still sent using kill(2),
as they ask for immediate shutdown.
This change is necessary to avoid triggering the ubf (unblocking
function) for rb_thread_call_without_gvl (and similar) functions
extensions. Most notably, this fixes compatibility with newer
versions of the 'pg' gem which will cancel a running DB query if
signaled[1].
This also has the nice side-effect of allowing a premature
master death (assuming preload_app didn't cause the master to
spawn off rogue child daemons).
Note: users should also refrain from using "killall" if using the
'pg' gem or something like it.
Unfortunately, this increases FD usage in the master as the writable
end of the pipe is preserved in the master. This limit the number
of worker processes the master may run to the open file limit of the
master process. Increasing the open file limit of the master
process may be needed. However, the FD use on the workers is
reduced by one as the internal self-pipe is no longer used. Thus,
overall pipe allocation for the kernel remains unchanged.
[1] - pg is correct to cancel a query, as it cannot know if
the signal was for a) graceful unicorn shutdown or
b) oh-noes-I-started-a-bad-query-ABORT-ABORT-ABORT!!
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Found via rdoc-spellcheck
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This means we no longer waste an extra file descriptor per
worker process in the master. Now there's no need to set a
higher file descriptor limit for systems running >= 1024
workers.
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This hopefully makes things easier to read, follow, and find
since it's mostly documentation...
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