This patch centralize the logic of creating & reading pid files into the
new pid_file module and improves upon / makes explicit a few race conditions
that existed with the previous code.
Starting Processes / Creating Pidfiles
======================================
Before this patch, we had three places that had very similar-looking
match lock_file::create_lock_file { ... }
blocks.
After this change, they can use a straight-forward call provided
by the pid_file:
pid_file::claim_pid_file_for_pid()
Stopping Processes / Reading Pidfiles
=====================================
The new pid_file module provides a function to read a pidfile,
called read_pidfile(), that returns a
pub enum PidFileRead {
NotExist,
NotHeldByAnyProcess(PidFileGuard),
LockedByOtherProcess(Pid),
}
If we get back NotExist, there is nothing to kill.
If we get back NotHeldByAnyProcess, the pid file is stale and we must
ignore its contents.
If it's LockedByOtherProcess, it's either another pidfile reader
or, more likely, the daemon that is still running.
In this case, we can read the pid in the pidfile and kill it.
There's still a small window where this is racy, but it's not a
regression compared to what we have before.
The NotHeldByAnyProcess is an improvement over what we had before
this patch. Before, we would blindly read the pidfile contents
and kill, even if no other process held the flock.
If the pidfile was stale (NotHeldByAnyProcess), then that kill
would either result in ESRCH or hit some other unrelated process
on the system. This patch avoids the latter cacse by grabbing
an exclusive flock before reading the pidfile, and returning the
flock to the caller in the form of a guard object, to avoid
concurrent reads / kills.
It's hopefully irrelevant in practice, but it's a little robustness
that we get for free here.
Maintain flock on Pidfile of ETCD / any InitialPidFile::Create()
================================================================
Pageserver and safekeeper create their pidfiles themselves.
But for etcd, neon_local creates the pidfile (InitialPidFile::Create()).
Before this change, we would unlock the etcd pidfile as soon as
`neon_local start` exits, simply because no-one else kept the FD open.
During `neon_local stop`, that results in a stale pid file,
aka, NotHeldByAnyProcess, and it would henceforth not trust that
the PID stored in the file is still valid.
With this patch, we make the etcd process inherit the pidfile FD,
thereby keeping the flock held until it exits.
Our shutdown procedure for "pageserver init" was buggy. Firstly, it
merely sent the process a SIGKILL, but did not wait for it to actually
exit. Normally, it should exit quickly as SIGKILL cannot be caught or
ignored by the target process, but it's still asynchronous and the
process can still be alive when the kill(2) call returns. Secondly,
"neon_local" removed the PID file after sending SIGKILL, even though the
process was still running. That hid the first problem: if we didn't
remove the PID file, and you start a new pageserver process while the
old one is still running, you would get an error when the new process
tries to lock the PID file.
We've been seeing a lot of "Cannot assign requested address" failures in
the CI lately. Our theory is that when we run "pageserver init"
immediately followed by "pageserver start", the first process is still
running and listening on the port when the second invocation starts up.
This commit hopefully fixes the problem.
It is generally a bad idea for the "neon_local" to remove the PID file
on the child process's behalf. The correct way would be for the server
process to remove the PID file, after it has fully shutdown everything
else. We don't currently have a robust way to ensure that everything has
truly shut down and closed, however.
A simpler way is to simply never remove the PID file. It's not necessary
to remove the PID file for correctness: we cannot rely on the cleanup to
happen anyway, if the server process crashes for example. Because of
that, we already have all the logic in place to deal with a stale PID
file that belonged to a process that already exited. Let's rely on that
on normal shutdown too.
Nothing interesting in these changes. Passing through the
RUST_BACKTRACE=full will hopefully save someone else panick reproduction
time.
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
* Fix https://github.com/neondatabase/neon/issues/1854
* Never log Safekeeper::conninfo in walproposer as it now contains a secret token
* control_panel, test_runner: generate and pass JWT tokens for Safekeeper to compute and pageserver
* Compute: load JWT token for Safekepeer from the environment variable. Do not reuse the token from
pageserver_connstring because it's embedded in there weirdly.
* Pageserver: load JWT token for Safekeeper from the environment variable.
* Rewrite docs/authentication.md
- Pass through FAILPOINTS environment variable to the pageserver in
"neon_local pageserver start" command
- On startup, list any failpoints that were set with FAILPOINTS to the log
- Add optional "extra_env_vars" argument to the NeonPageserver.start()
function in the python fixture, so that you can pass FAILPOINTS
None of the tests use this functionality yet; that comes in a separate
commit.
closes https://github.com/neondatabase/neon/pull/2865
* Poll more frequently when waiting for process start/stop. This
speeds up startup and shutdown in tests. We did this already in
commit 52ce1c9d53, which reduced the interval to 100 ms, but it was
inadvertently increased back to 500 ms in commit d42700280f. Reduce
it to 100 ms again, for both start and stop operations.
* Harmonize the start and stop loops, printing the dots and notices
the same way in both. I considered extracting the logic to a
separate retry-function that takes a closure as argument that does
the polling, but as long as we only have two copies, the code
duplication isn't that bad.
* Remove newline after "Starting pageserver" and "Starting etcd"
messages, so that the progress-indicator dots that are printed once
a second are printed on the same line. Before:
Starting pageserver at '127.0.0.1:64000' in '.neon'
...
pageserver started, pid: 2538937
After:
Starting pageserver at '127.0.0.1:64000' in '.neon'...
pageserver started, pid: 2538937
The "Starting safekeeper" message already got this right.
* Update example output in README.md to match
