You can replace an NGINX binary without intentionally dropping active connections by running the old and new master processes together, checking the new generation, draining the old workers with SIGWINCH, and retiring the old master with SIGQUIT. The handoff is controlled by signals, not by stopping the service.
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The safe sequence is: validate the replacement, preserve the old executable and PID state, send SIGUSR2 to create the second generation, verify real traffic and workers, drain the old generation, then remove it. If the new binary fails, the retained old master and executable provide a rollback path.
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What an in-place NGINX upgrade actually changes
An NGINX upgrade replaces the executable used by the master and worker processes. A conventional service restart stops those processes first, which can close listening sockets and interrupt requests. An on-the-fly binary upgrade avoids that stop-start gap.
After SIGUSR2, the existing master renames its PID file with an .oldbin suffix and starts a new master from the replacement executable. The two generations overlap and can hold the same listening sockets. New workers can accept work while old workers finish requests that were already in progress.
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This does not make every connection immortal. A client can still experience an error caused by an application failure, an upstream timeout, a network interruption, a protocol-level close, or an incorrectly configured replacement. The upgrade procedure prevents the planned NGINX handoff from being the cause of a drop.
Signals and process states
Use the master-process PID, not a worker PID, for the handoff signals. The PID file location is defined by your NGINX build or configuration, so identify it before beginning.
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|---|---|---|---|
SIGUSR2 |
Current master | Renames the current PID file to an .oldbin form and starts a new master and workers from the replacement executable. |
Begin the binary handoff after validation and installation. |
SIGWINCH |
Old master recorded in the .oldbin PID file |
Asks old workers to shut down gracefully. They stop accepting new work and finish active requests and connections. | Drain the old generation after the new one passes health checks. |
SIGQUIT |
Old master | Retires the old generation after its workers have drained. | Complete the upgrade only after the new generation is demonstrably healthy. |
SIGHUP |
Old master during rollback | Starts the old workers again without rereading configuration, according to NGINX’s binary-upgrade procedure. | Restore service with the old generation when the replacement is faulty. |
Signals are asynchronous. Sending one does not prove that the requested state has already been reached; inspect process lists, PID files, logs, health checks, and representative traffic between stages.
Prepare before replacing the executable
Record the current state
Write down the running NGINX version, the master PID, the worker PIDs, the executable path, the configuration path, and the listening addresses and ports. Capture the currently loaded modules as well. A module compiled for a different NGINX version or build options can prevent the new binary from starting or can change request behavior after the handoff.
Keep a terminal or monitoring view open for process and application health. You need to distinguish the old master, the new master, and their workers once both generations exist.
Preserve rollback material
Copy the current executable to a protected rollback location before installing the replacement. Keep the existing master process and its .oldbin PID state until the upgrade is accepted. For a package-managed NGINX Plus deployment, back up the NGINX configuration and logs as part of the package runbook.
Do not overwrite the only copy of the old executable. If the replacement fails after SIGUSR2, the old master can only restart old workers reliably when the old binary and its process state remain available.
Build or obtain a compatible replacement
Use a replacement that matches the required operating-system libraries, compile-time options, dynamic modules, TLS support, and other dependencies of the running service. Compatibility is not limited to the version string: a binary can start successfully while a required module is absent or built for an incompatible ABI.
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Install the replacement in the path used by the service, but retain the rollback copy. If you use a symlink or an atomic file replacement, confirm which path the current master and the service manager actually execute; changing an unrelated copy has no effect on the running process.
Test the replacement against the live configuration
Run the configuration test with the replacement executable, using the same configuration file and include paths as the live service. The test must be performed by the new binary, not merely by the old command that happens to be first in your shell’s PATH.
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PIDFILE=/run/nginx.pid
CONF=/etc/nginx/nginx.conf
NEW_NGINX=/usr/sbin/nginx
sudo "$NEW_NGINX" -t -c "$CONF"Proceed only when the test reports a valid configuration and the expected modules can be loaded. A successful syntax test does not replace traffic testing, so treat it as a gate before the process handoff rather than as final proof.
Perform the no-drop binary handoff
1. Install the replacement and check the running master
Place the validated executable at the live service path. Confirm that the old master is still running and that the PID file contains the expected master PID. Save that PID before sending any signal.
PIDFILE=/run/nginx.pid
OLD_MASTER=$(cat "$PIDFILE")
printf 'Current master: %sn' "$OLD_MASTER"
ps -o pid,ppid,cmd -p "$OLD_MASTER"Use the PID file configured for your installation; distributions and custom builds may use different locations.
2. Start the second generation with SIGUSR2
Send SIGUSR2 to the current master. NGINX renames the original PID file to an .oldbin form and launches a new master and workers from the replacement executable.
sudo kill -USR2 "$OLD_MASTER"Do not send SIGWINCH or SIGQUIT immediately afterward. The old generation must remain available while you prove that the new generation started correctly.
3. Verify the new master and workers
Check for the new master PID in the active PID file and the old master PID in the corresponding .oldbin file. Confirm that the new workers are children of the new master and that the executable and modules reported by the new process match the intended release.
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Then test the service through the same path used by clients. Include representative virtual hosts, TLS listeners, authentication paths, static content, reverse-proxy routes, and any health endpoint that exercises upstream connectivity. Review error logs and upstream logs while sending normal test traffic. A process that exists but cannot serve a configured listener is not a successful upgrade.
- The new master process exists and has the expected PID relationship.
- New workers are running and remain running during observation.
- Expected listening sockets are available to the new generation.
- The replacement version and required modules are present.
- Health checks pass through each important listener and route.
- Representative requests complete without new NGINX or upstream errors.
Only after these checks pass should you begin draining the old generation.
4. Drain old workers with SIGWINCH
Read the old master PID from the .oldbin PID file and send it SIGWINCH. The old master tells its workers to shut down gracefully. They stop taking new work while existing requests and connections finish.
OLD_PIDFILE=/run/nginx.pid.oldbin
OLD_MASTER=$(cat "$OLD_PIDFILE")
sudo kill -WINCH "$OLD_MASTER"Keep watching the old worker count and active connection metrics. Short requests may disappear quickly; long-lived requests, WebSockets, keepalive sessions, slow clients, and busy upstreams can keep workers alive considerably longer.
5. Retire the old master with SIGQUIT
When old workers have drained and the new generation continues to pass health checks, send SIGQUIT to the old master.
sudo kill -QUIT "$OLD_MASTER"After the old master exits, confirm that only the new master and its workers remain. Check that the ordinary PID file now represents the active generation and that the .oldbin state is no longer needed. Keep the rollback executable until your operational acceptance period is complete, then remove it according to your change-control policy.
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The old and new masters overlap while they share the listening sockets. The new workers can accept new connections, while old workers continue handling requests that they already accepted. The graceful worker shutdown requested by SIGWINCH avoids an intentional close of those active requests.
Connection survival depends on reaching the signals in the correct order. If you stop the service first, kill workers forcibly, replace a binary that cannot load its modules, or retire the old master before the new workers are ready, the overlap protection is lost. A graceful upgrade also cannot prevent an application from closing a connection or a client from timing out independently.
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Rollback when the new generation is bad
Rollback is easiest while the old executable, old master, and .oldbin PID file are still present. Stop treating the replacement as accepted as soon as health checks, logs, or real traffic show a regression.
Restore old workers
Send SIGHUP to the old master. In the documented binary-upgrade flow, this starts the old workers again without rereading the configuration. That distinction matters: the rollback is intended to restore the known-good generation rather than introduce an unverified configuration reload at the same time.
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OLD_MASTER=$(cat "$OLD_PIDFILE")
sudo kill -HUP "$OLD_MASTER"Shut down the faulty new generation
Once old workers are serving again, gracefully shut down the new master. Identify the new master from the active PID file or process tree rather than guessing from worker PIDs. If the new master cannot be controlled normally, terminating it allows the old master to resume workers, but a forced termination should be treated as an emergency recovery action because it can interrupt work owned by the new generation.
After rollback, verify the old version, modules, listeners, health checks, and representative traffic. Do not delete the replacement immediately if you need logs or process evidence to diagnose the failure.
How long should the drain take?
There is no universal sleep interval for this procedure. Drain time is determined by request duration, WebSocket and other long-lived connections, keepalive behavior, worker load, client speed, upstream response time, and host scheduling.
Automation should wait for observable conditions instead of sleeping for an arbitrary number of seconds. Useful gates include:
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- The new master PID is present and stable.
- The expected new workers remain running.
- Health checks and representative requests continue to pass for an observation window appropriate to your service.
- Old worker processes have exited or the remaining connections are understood and intentionally allowed to continue.
- Error rates, latency, upstream failures, and connection counts remain within your normal operating thresholds.
If old workers do not drain, inspect long-lived connections and active requests before taking action. Sending a forceful termination to meet a timer defeats the purpose of a graceful upgrade.
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The signal choreography is the same conceptually, but the preparation and support model differ.
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| Decision axis | Manual binary upgrade | Package-managed NGINX Plus upgrade |
|---|---|---|
| Rollback control | You retain the previous executable directly and control when it is replaced or restored. | Use the package manager’s available versions and preserve the prior package and configuration according to the distribution runbook. |
| Repository and credentials | Requires the binary source or build process you selected; no package repository is implied. | Requires the official repository configuration and credentials for the installation. |
| Module and version compatibility | You must validate compile-time options, dynamic modules, libraries, and the target configuration yourself. | Check package contents and the release notes for source and target versions, including version-specific changes. |
| Backups | At minimum, retain the old executable and PID state; preserve configuration and logs as part of your change procedure. | Back up /etc/nginx and logs before using the operating system package manager. |
| Automation | Expose each signal and verify each process transition explicitly. | Combine package-manager transaction checks with the same PID, worker, health, and drain gates. |
| Operational support | Your team owns the build, compatibility checks, and rollback artifacts. | Follow the vendor’s distribution instructions and release notes in addition to the graceful handoff checks. |
Do not assume that installing a package completes the no-drop procedure by itself. The package transaction changes files; the controlled overlap, verification, drain, and retirement still need to be observed.
Automating the runbook safely
A reliable automation job should be state-aware and abortable. Separate the workflow into stages so a failed check leaves the old generation available.
- Capture state: record the current version, executable path, configuration path, master PID, worker list, listeners, and module expectations.
- Stage artifacts: copy the old executable, install the replacement, and retain configuration and log backups required by your deployment model.
- Validate: run
nginx -tthrough the replacement executable and stop if it fails. - Handoff: send
SIGUSR2to the recorded old master. - Observe: wait for the new PID and workers, then run health and traffic checks. Abort and roll back if any gate fails.
- Drain: send
SIGWINCHto the old master and wait for old workers to leave, allowing for known long-lived sessions. - Retire: send
SIGQUITonly after the new generation remains healthy and the drain condition is satisfied. - Record: save final PIDs, version output, check results, and any warnings for the change record.
Make each wait interruptible and report the state that caused a timeout. A script that says only “sleep, then quit” can retire a healthy rollback path before the replacement has been observed.
Troubleshooting common failure modes
The new master never appears
Check the error log, executable permissions, linked libraries, module loading, configuration paths, and the PID-file location. Confirm that the binary you tested is the binary installed at the service path. Keep the old master running while correcting the problem; do not send the retirement signals.
The new master starts but workers exit
Inspect startup and error logs for module, privilege, resource, and upstream configuration errors. Re-run the replacement’s configuration test with the exact live include paths. Worker exit is a failed verification state even when the master PID exists.
Both generations appear healthy but old workers remain
Look for WebSockets, slow requests, keepalive sessions, large uploads, or blocked upstream responses. Measure active connections and request duration. Allow the known sessions to finish rather than converting the graceful drain into a forced kill.
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Traffic fails after the handoff
Stop the retirement sequence, preserve the old PID and executable, and begin rollback. Compare listener bindings, loaded modules, TLS settings, proxy behavior, and error rates between generations. A syntax-pass does not prove behavioral compatibility.
The PID files are confusing
Use the process parent-child tree and the configured PID path to identify masters. The original master is associated with the .oldbin PID file during the overlap; the active PID file belongs to the new generation. Never send a signal to a worker merely because its command line contains NGINX.
Quick Recap
Final preflight and completion checklist
- Old executable copied and recoverable.
- Configuration, logs, and package backups made where required.
- Replacement modules and build options checked.
- Replacement executable passed its own
nginx -tagainst the live configuration. - Current master PID recorded before
SIGUSR2. - New master and workers verified before draining.
- Representative traffic and health checks passed.
SIGWINCHsent only to the old master from the.oldbinPID state.- Drain observed rather than assumed.
SIGQUITsent only after the new generation was accepted.- Final process, version, listener, and error-log checks completed.
- Rollback artifacts retained for the agreed acceptance period.
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