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daemon/command: add support for sd_notify "reload" notifications
commit f74b856 added an [ExecReload] to the systemd unit, which allows users to signal the daemon to reload its config through systemd (`systemctl reload docker.service`). While reloading works, systemd expects the `ExecReload` command to be synchronous, so that it knows when the reload completes, and can account for this when managing dependent services. > Note however that reloading a daemon by enqueuing a signal (...) is usually > not a good choice, because this is an asynchronous operation and hence not > suitable when ordering reloads of multiple services against each other. Systemd 253 introduced a new Type (Type=notify-reload, see [systemd#25916]), which allows setting a "ReloadSignal" instead, if the service supports it by including a [MONOTONIC_USEC] value in its "RELOADING=1" notifications. This patch: - adds reload notifications to the daemon to notify when the daemon got signaled to reload its configuration see [sd_notify(3)]. - appends a [MONOTONIC_USEC] value to the reload notification to support systemd 253's notify-reload protocol. This is backwards-compatible with older systemd releases as the systemd service manager ignores unknown assignments in notifications. - adds a `notifyReady` callback to notify when the reload finished, which we currently send regardless if the reload was successful or failed (which could be due to an invalid config). [ExecReload]: https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#ExecReload= [systemd#25916]: systemd/systemd#25916 [MONOTONIC_USEC]: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#MONOTONIC_USEC=… [sd_notify(3)]: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#RELOADING=1 Signed-off-by: Cory Snider <[email protected]> Co-authored-by: Sebastiaan van Stijn <[email protected]> Signed-off-by: Sebastiaan van Stijn <[email protected]>
1 parent 0e52362 commit af18206

4 files changed

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‎daemon/command/daemon.go‎

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@@ -521,6 +521,13 @@ func (cli *daemonCLI) reloadConfig() {
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}
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}
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// On Linux, we use sd_notify to indicate we're reloading config. We send
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// this signal as early as possible to let systemd know we're reloading,
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// but must signal "ready" after this completes (even on failure), which
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// is done by the reload function defined above.
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done := notifyReloading()
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defer done()
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if err := config.Reload(*cli.configFile, cli.flags, reload); err != nil {
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log.G(ctx).WithError(err).Error("Error reloading configuration")
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return

‎daemon/command/daemon_freebsd.go‎

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@@ -11,6 +11,10 @@ func preNotifyReady() error {
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func notifyReady() {
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}
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// notifyReloading sends a message to the host when the server got signaled to
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// reloading its configuration. It is a no-op on FreeBSD.
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func notifyReloading() func() { return func() {} }
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// notifyStopping sends a message to the host when the server is shutting down
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func notifyStopping() {
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}

‎daemon/command/daemon_linux.go‎

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@@ -58,6 +58,25 @@ func notifyStopping() {
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_, _ = systemdDaemon.SdNotify(false, systemdDaemon.SdNotifyStopping)
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}
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// notifyReloading sends a message to the host when the server got signaled to
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// reloading its configuration, see [sd_notify(3)]. The server should be running
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// as a systemd unit with "Type=notify" or "Type=notify-reload" (see
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// [systemd.service(5)]).
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//
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// notifyReloading returns a callback that must be called after reloading completes
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// (either successfully or unsuccessfully) to send [notifyReady].
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//
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// [sd_notify(3)]: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#RELOADING=1
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// [systemd.service(5)]: https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#Type=
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func notifyReloading() (done func()) {
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sent, _ := systemdDaemon.SdNotify(false, systemdDaemon.SdNotifyReloading+"\n"+systemdDaemon.SdNotifyMonotonicUsec())
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if !sent {
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// Nothing to do if no reloading event was sent.
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return func() {}
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}
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return notifyReady
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}
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func validateCPURealtimeOptions(cfg *config.Config) error {
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if cfg.CPURealtimePeriod == 0 && cfg.CPURealtimeRuntime == 0 {
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return nil

‎daemon/command/daemon_windows.go‎

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@@ -56,6 +56,10 @@ func preNotifyReady() error {
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func notifyReady() {
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}
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// notifyReloading sends a message to the host when the server got signaled to
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// reloading its configuration. It is a no-op on Windows.
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func notifyReloading() func() { return func() {} }
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// notifyStopping sends a message to the host when the server is shutting down
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func notifyStopping() {
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}

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