This one was scheduled for removal in 2.3 since 2.2-dev3 by commit
1b85785bc ("MINOR: config: mark global.debug as deprecated"). Let's
remove it now. It remains totally possible to use -d on the command
line though.
This was introduced 15 years ago or so to delay the stopping of some
services so that a monitoring device could detect its port being down
before services were stopped. Since then, clean reloads were implemented
and this doesn't cope well with reload at all, preventing the new process
from seamlessly binding, and forcing processes to coexist with half-baked
configurations.
Now it has become a real problem because there's a significant code
portion in the proxies that is solely dedicated to this obsolete feature,
and dealing with its special cases eases the introduction of bugs in
other places so it's about time that it goes.
We could tentatively schedule its removal for 2.4 with a hard deadline
for 2.5 in any case.
Now we have ->suspend() and ->resume() for listeners at the protocol
level. This means that it now becomes possible for a protocol to redefine
its own way to suspend and resume. The default functions are provided for
TCP, UDP and unix, and they are pass-through to the receiver equivalent
as it used to be till now. Nothing was defined for sockpair since it does
not need to suspend/resume during reloads, hence it will succeed.
The inner part now goes into the protocol and is used to decide how to
unbind a given protocol's listener. The existing code which is able to
also unbind the receiver was provided as a default function that we
currently use everywhere. Some complex listeners like QUIC will use this
to decide how to unbind without impacting existing connections, possibly
by setting up other incoming paths for the traffic.
This is used as a generic way to unbind a receiver at the end of
do_unbind_listener(). This allows to considerably simplify that function
since we can now let the protocol perform the cleanup. The generic code
was moved to sock.c, along with the conditional rx_disable() call. Now
the code also supports that the ->disable() function of the protocol
which acts on the listener performs the close itself and adjusts the
RX_F_BUOND flag accordingly.
This listener flag indicates whether the receiver part of the listener
is specific to the master or to the workers. In practice it's only used
by the master's CLI right now. It's used to know whether or not the FD
must be closed before forking the workers. For this reason it's way more
of a receiver's property than a listener's property, so let's move it
there under the name RX_F_MWORKER. The rest of the code remains
unchanged.
And also remove it from its callers. This subtle distinction was added as
sort of a hack for the seamless reload feature but is not needed anymore
since the do_close turned unused since commit previous commit ("MEDIUM:
listener: let do_unbind_listener() decide whether to close or not").
This also removes the unbind_listener_no_close() function.
The listener contains all the information needed to decide to close on
unbind or not. The rule is the following (when we're not stopping):
- worker process unbinding from a worker's FD with socket transfer enabled => keep
- master process unbinding from a master's inherited FD => keep
- master process unbinding from a master's FD => close
- master process unbinding from a worker's FD => close
- worker process unbinding from a master's FD => close
- worker process unbinding from a worker's FD => close
Let's translate that into the function and stop using the do_close
argument that is a bit obscure for callers. It was not yet removed
to ease code testing.
BROKEN: the failure rate on reg-tests/seamless-reload/abns_socket.vtc has
significantly increased for no obvious reason. It fails 99% of the time vs
10% before.
do_unbind_listener() is not logical and is not even idempotent. It must
not touch the fd if already -1, which also means not touch the receiver.
In addition, when performing a partial stop on a socket (not closing),
we know the socket remains in the listening state yet it's marked as
LI_ASSIGNED, which is confusing as it doesn't translate its real state.
With this change, we make sure that FDs marked for close end up in
ASSIGNED state and that those which are really bound and on which a
listen() was made (i.e. not pause) remain in LISTEN state. This is what
is closest to reality.
Ideally this function should become a default proto->unbind() one but
it may still keep a bit too much state logic to become generalized to
other protocols (e.g. QUIC).
Right now in enable_listener(), we used to start all enabled
listeners then kill from the workers those that were for the master.
But this is incomplete. We must also close from the master the
listeners that are solely for workers, and do it before we even
start them. Otherwise we end up with a master responding to the
worker CLI connections if the listener remains in listen mode to
translate the socket's real state.
It doesn't seem like it could have caused bugs in the past because we
used to aggressively mark disabled listeners as LI_ASSIGNED despite
the fact that they were still bound and listening. If this patch were
ever seen as a candidate solution for any obscure bug, be careful in
that it subtly relies on the fact that fd_delete() doesn't close
inherited FDs anymore, otherwise that could break the master's ability
to pass inherited FDs on reloads.
In Linux kernel's net/ipv4/udp.c there's a udp_disconnect() function
which is called when connecting to AF_UNSPEC, and which unhashes a
"connection". This property, which is also documented in connect(2)
both in Linux and Open Group's man pages for datagrams, is interesting
because it allows to reverse a connect() which is in fact a filter on
the source. As such we can suspend a receiver by making it connect to
itself, which will cause it not to receive any traffic anymore, letting
a new one receive it all, then resume it by breaking this connection.
This was tested to work well on Linux, other operating systems should
also be tested. Before this, sending a SIGTTOU to a process having a
UDP syslog forwarder would cause this error:
[WARNING] 280/194249 (3268) : Paused frontend GLOBAL.
[WARNING] 280/194249 (3268) : Some proxies refused to pause, performing soft stop now.
[WARNING] 280/194249 (3268) : Proxy GLOBAL stopped (cumulated conns: FE: 0, BE: 0).
[WARNING] 280/194249 (3268) : Proxy sylog-loadb stopped (cumulated conns: FE: 0, BE: 0).
With this change, it now proceeds just like with TCP listeners:
[WARNING] 280/195503 (3885) : Paused frontend GLOBAL.
[WARNING] 280/195503 (3885) : Paused frontend sylog-loadb.
And SIGTTIN also works:
[WARNING] 280/195507 (3885) : Resumed frontend GLOBAL.
[WARNING] 280/195507 (3885) : Resumed frontend sylog-loadb.
On Linux this also works with TCP listeners (which can then be resumed
using listen()) and established TCP sockets (which we currently kill
using setsockopt(so_linger)), both not being portable on other OSes.
UNIX sockets and ABNS sockets do not support it however (connect
always fails). This needs to be further explored to see if other OSes
might benefit from this to perform portable and reliable resets
particularly on the backend side.
One difficulty in soft-stopping is to make sure not to forget unlisted
listeners. By first doing a pass using protocol_stop_now() we catch the
vast majority of them. The few remaining ones are the ones belonging to
a proxy having a grace period. For these ones, the proxy will arm its
stop_time timer and emit a log message.
Since neither UDP listeners nor peers use the grace period, we can already
get rid of the special cases there since we know they will have been stopped
by the protocols.
This will instantly stop all listeners except those which belong to
a proxy configured with a grace time. This means that UDP listeners,
and peers will also be stopped when called this way.
There are multiple ways a proxy may switch to the disabled state,
but now it's essentially once it loses its last listener. Instead
of keeping duplicate code around and reporting the state change
before actually seeing it, we now report it at the moment it's
performed (from the last listener leaving) which allows to remove
the message from all other places.
For now we cannot easily distinguish a peers frontend from another one,
which will be problematic to avoid reporting them when stopping their
listeners. Let's add PR_MODE_PEERS for this. It's not supposed to cause
any issue since all non-HTTP proxies are handled similarly now.
This function will be used to definitely stop a listener (e.g. during a
soft_stop). This is actually tricky because it may be called for a proxy
or for a protocol, both of which require locks and already hold some. The
function takes booleans indicating which ones are already held, hoping
this will be enough. It's not well defined wether proto->disable() and
proto->rx_disable() are supposed to be called with any lock held, and
they are used from do_unbind_listener() with all these locks. Some back
annotations ought to be added on this point.
The proxy's listeners count is updated, and the proxy is marked as
disabled and woken up after the last one is gone. Note that a
listener in listen state is already not attached anymore since it
was disabled.
We have to count unstoppable jobs which correspond to worker sockpairs, in
order to know when to count. However the way it's currently done is quite
awkward because these are counted when stopping making the stop mechanism
non-idempotent. This is definitely something we want to fix before stopping
by protocol or our listeners count will quickly go wrong. Now they are
counted when the listeners are created.
We'll need an already locked variant of this function so let's make
__delete_listener() which will be called with the protocol lock held
and the listener's lock held.
At each place we used to manipulate the FDs directly we can now call
the listener protocol's enable/disable/rx_enable/rx_disable depending
on whether the state changes on the listener or the receiver. One
exception currently remains in listener_accept() which is a bit special
and which should be split into 2 or 3 parts in the various protocol
layers.
The test of fd_updt in do_unbind_listener() that was added by commit
a51885621 ("BUG/MEDIUM: listeners: Don't call fd_stop_recv() if fd_updt
is NULL.") could finally be removed since that part is correctly handled
in the low-level disable() function.
One disable() was added in resume_listener() before switching to LI_FULL
because rx_resume() enables polling on the FD for the receiver while
we want to disable it if the listener is full. There are different
ways to clean this up in the future. One of them could be to consider
that TCP receivers only act at the listener level. But in fact it does
not translate reality. The reality is that only the receiver is paused
and that the listener's state ought not be affected here. Ultimately
the resume_listener() function should be split so that the part
controlled by the protocols only acts on the receiver, and that the
receiver itself notifies the upper listener about the change so that
the listener protocol may decide to disable or enable polling. Conversely
the listener should automatically update its receiver when they share the
same state. Since there is no harm proceeding like this, let's keep this
for now.
These methods will be used to enable/disable accepting new connections
so that listeners do not play with FD directly anymore. Since all the
currently supported protocols work on socket for now, these are identical
to the rx_enable/rx_disable functions. However they were not defined in
sock.c since it's likely that some will quickly start to differ. At the
moment they're not used.
We have to take care of fd_updt before calling fd_{want,stop}_recv()
because it's allocated fairly late in the boot process and some such
functions may be called very early (e.g. to stop a disabled frontend's
listeners).
These methods will be used to enable/disable rx at the receiver level so
that callers don't play with FDs directly anymore. All our protocols use
the generic ones from sock.c at the moment. For now they're not used.
These will be used on receivers, to enable or disable receiving on a
listener, which most of the time just consists in enabling/disabling
the file descriptor.
We have to take care of the existence of fd_updt to know if we may
or not call fd_{want,stop}_recv() since it's not permitted in very
early boot.
Instead of calling listen() for IPPROTO_TCP in resume_listener(), let's
call the protocol's ->rx_resume() method when defined, which does the same.
This removes another hard-dependency on the fd and underlying protocol
from the generic functions.
This one undoes ->rx_suspend(), it tries to restore an operational socket.
It was only implemented for TCP since it's the only one we support right
now.
The ->pause method is inappropriate since it doesn't exactly "pause" a
listener but rather temporarily disables it so that it's not visible at
all to let another process take its place. The term "suspend" is more
suitable, since the "pause" is actually what we'll need to apply to the
FULL and LIMITED states which really need to make a pause in the accept
process. And it goes well with the use of the "resume" function that
will also need to be made per-protocol.
Let's rename the function and make it act on the receiver since it's
already what it essentially does, hence the prefix "_rx" to make it
more explicit.
The protocol struct was a bit reordered because it was becoming a real
mess between the parts related to the listeners and those for the
receivers.
Since the listeners were split into receiver+listener, this field ought
to have been renamed because it's confusing. It really links receivers
and not listeners, as most of the time it's used via rx.proto_list!
The nb_listeners field was updated accordingly.
protocol_enable_all() calls proto->enable_all() for all protocols,
which is always equal to enable_all_listeners() which in turn simply is
a generic loop calling enable_listener() always returning ERR_NONE. Let's
clean this madness by first calling enable_listener() directly from
protocol_enable_all().
These ones have never been called, they were referenced by the protocol's
disable_all for some protocols but there are no traces of their use, so
in addition to not being sure the code works, it has never been tested.
Let's remove a bit of complexity starting from there.
fd_stop_recv() has nothing to do in the generic listener code, it's per
protocol as some don't need it. For instance with abns@ it could even
lead to fd_stop_recv(-1). And later with QUIC we don't want to touch
the fd at all! It used to be that since commit f2cb169487 delegating
fd manipulation to their respective threads it wasn't possible to call
it down there but it's not the case anymore, so let's perform the action
in the protocol-specific code.
By using the same "ret" variable in the "if" block to test the return
value of pause(), the second one shadows the first one and when forcing
the result to zero in case of an error, it doesn't do anything. The
problem is that some listeners used to fail to pause in multi-process
mode and this was not reported, but their failure was automatically
resolved by the last process to pause. By properly checking for errors
we might now possibly report a race once in a while so we may have to
roll this back later if some users meet it.
The test on ==0 is wrong too since technically speaking a total stop
validates the need for a pause, but stops the listener so it's just
the resume that won't work anymore. We could switch to stopped but
it's an involuntary switch and the user will not know. Better then
mark it as paused and let the resume continue to fail so that only
the resume will eventually report an error (e.g. abns@).
This must not be backported as there is a risk of side effect by fixing
this bug, given that it hides other bugs itself.
In multi-process, the TCP pause is very brittle and we never noticed
it because the error was lost in the upper layers. The problem is that
shutdown() may fail if another process already did it, and will cause
a process to fail to pause.
What we do here in case of error is that we double-check the socket's
state to verify if it's still accepting connections, and if not, we
can conclude that another process already did the job in parallel.
The difficulty here is that we're trying to eliminate false positives
where some OSes will silently report a success on shutdown() while they
don't shut the socket down, hence this dance of shutw/listen/shutr that
only keeps the compatible ones. Probably that a new approach relying on
connect(AF_UNSPEC) would provide better results.
When temporarily pausing the listeners with SIG_TTOU, we now pause
all listeners via the protocols instead of the proxies. This has the
benefits that listeners are paused regardless of whether or not they
belong to a visible proxy. And for resuming via SIG_TTIN we do the
same, which allows to report binding conflicts and address them,
since the operation can be repeated on a per-listener basis instead
of a per-proxy basis.
While in appearance all cases were properly handled, it's impossible
to completely rule out the possibility that something broken used to
work by luck due to the scan ordering which is naturally different,
hence the major tag.
These two functions are used to pause and resume all listeners of
all protocols. They use the standard listener functions for this
so they're supposed to handle the situation gracefully regardless
of the upper proxies' states, and they will report completion on
proxies once the switch is performed.
It might be nice to define a particular "failed" state for listeners
that cannot resume and to count them on proxies in order to mention
that they're definitely stuck. On the other hand, the current
situation is retryable which is quite appreciable as well.
Till now, we used to call pause_proxy()/resume_proxy() to enable/disable
processing on a proxy, which is used during soft reloads. But since we want
to drive this process from the listeners themselves, we have to instead
proceed the other way around so that when we enable/disable a listener,
it checks if it changed anything for the proxy and notifies about updates
at this level.
The detection is made using li_ready=0 for pause(), and li_paused=0
for resume(). Note that we must not include any test for li_bound because
this state is seen by processes which share the listener with another one
and which must not act on it since the other process will do it. As such
the socket behind the FD will automatically be paused and resume without
its local state changing, but this is the limit of a multi-process system
with shared listeners.
It's quite confusing to have the test on LI_READY very low in the function
as it should be made much earlier. Just like with previous commit, let's
do it when entering. The additional states, however (limited, full) continue
to go through the whole function.
It's better not to try to perform pause() actions on wrong states, so
let's check this and make sure that all callers are now safe. This
means that we must not try to pause a listener which is already paused
(e.g. it could possibly fail if the pause operation isn't idempotent at
the socket level), nor should we try it on earlier states.
The two functions don't need to be distinguished anymore since they have
all the necessary info to act as needed on their listeners. Let's just
pass via stop_proxy() and make it check for each listener which one to
close or not.
Its sole remaining purpose was to display "proxy foo started", which
has little benefit and pollutes output for those with plenty of proxies.
Let's remove it now.
The VTCs were updated to reflect this, because many of them had explicit
counts of dropped lines to match this message.
This is tagged as MEDIUM because some users may be surprized by the
loss of this quite old message.
The remaining proxy states were only used to distinguish an enabled
proxy from a disabled one. Due to the initialization order, both
PR_STNEW and PR_STREADY were equivalent after startup, and they
would only differ from PR_STSTOPPED when the proxy is disabled or
shutdown (which is effectively another way to disable it).
Now we just have a "disabled" field which allows to distinguish them.
It's becoming obvious that start_proxies() is only used to print a
greeting message now, that we'd rather get rid of. Probably that
zombify_proxy() and stop_proxy() should be merged once their
differences move to the right place.
The enabled/disabled config options were stored into a "state" field
that is an integer but contained only PR_STNEW or PR_STSTOPPED, which
is a bit confusing, and causes a dependency with proxies. This was
renamed to "disabled" and is used as a boolean. The field was also
moved to the end of the struct to stop creating a hole and fill another
one.
Instead of looking at listeners in proxies in PR_STNEW state, we'd
rather check for listeners in those not in PR_STSTOPPED as it's only
this state which indicates the proxy was disabled. And let's check
the listeners count instead of testing the list's head.
This state was used to mention that a proxy was in PAUSED state, as opposed
to the READY state. This was causing some trouble because if a listener
failed to resume (e.g. because its port was temporarily in use during the
resume), it was not possible to retry the operation later. Now by checking
the number of READY or PAUSED listeners instead, we can accurately know if
something went bad and try to fix it again later. The case of the temporary
port conflict during resume now works well:
$ socat readline /tmp/sock1
prompt
> disable frontend testme3
> disable frontend testme3
All sockets are already disabled.
> enable frontend testme3
Failed to resume frontend, check logs for precise cause (port conflict?).
> enable frontend testme3
> enable frontend testme3
All sockets are already enabled.
This state is only set when a pause() fails but isn't even set when a
resume() fails. And we cannot recover from this state. Instead, let's
just count remaining ready listeners to decide to emit an error or not.
It's more accurate and will better support new attempts if needed.
