Step 01 of 06
Learn the concept
Production rarely ends with Ctrl-C and a clean conscience. Supervisors send SIGTERM, wait a deadline, then use SIGKILL if the process refuses to leave. Kubernetes calls that deadline terminationGracePeriodSeconds; course four will make it very real.
The ideas this is made of
Signals are process-level messages
SIGTERM is the standard polite stop signal. SIGINT usually comes from Ctrl-C. SIGKILL cannot be caught, delayed or cleaned up after. Your code only gets a chance to close databases and drain requests if it responds to catchable signals before the outside system loses patience.
NotifyContext connects signals to Go cancellation
signal.NotifyContext returns a context cancelled when selected signals arrive. Passing that context to the scheduler, server and checks creates one stop line through the process. Remember to call the returned stop function so signal handling is released during cleanup.
HTTP shutdown is not server close
Server.Close drops active connections. Server.Shutdown(ctx) first closes listeners so new requests stop, then waits for active handlers until the context deadline. That is the behaviour users expect during deploys: no new work, but current requests get a fair chance.
Kubernetes will not wait forever
In Kubernetes, a pod receives SIGTERM and has terminationGracePeriodSeconds, often 30s, before SIGKILL. If Beacon needs 45s to drain, Kubernetes will cut it off. Designing a 25s shutdown deadline inside a 30s grace period leaves room for runtime and network slop.
package main
import (
"context"
"fmt"
"os"
"os/signal"
"syscall"
)
func main() {
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()
<-ctx.Done()
fmt.Println("shutdown requested")
}The program waits until a signal cancels the context. Beacon will use the same cancellation to stop the scheduler and begin HTTP server shutdown.
Stop signals
| Signal | Catchable | Use |
|---|---|---|
SIGINT | Yes | Terminal interrupt |
SIGTERM | Yes | Supervisor stop |
SIGKILL | No | Forced kill |
SIGHUP | Yes | Reload in some daemons |
What these are called on the job
Drain — Let in-flight work finish while refusing new work.
SIGTERM — A catchable request for a process to terminate.
SIGKILL — An uncatchable forced process kill.