xr09 / flare

Debug how containers react to signals

Flare

Flare is a tool to debug how containers are reacting to signals.

Why use Flare

The idea is to be able to determine if SIGTERM signals are reaching the processes inside containers for them to be able to terminate gracefully.

After running this image the flare process will print its PID and wait for signals.

Signals captured:

• SIGUSR1: will print to stdout
• SIGINT: will print to stdout and exit the program (keyboard interruption)
• SIGTERM: will print to stdout and exit the program

Usage

Flare takes 1 positional parameter called sleep_time, this will be the amount of time the program will take to close its unfinished business when receiving a TERM signal, emulating this way a real world workload.

❯ ./flare 5
Flare running with PID 91082

received SIGTERM
the program will take 5s to finish correctly
...
SUCCESS: the program had enough time to finish

Flare on Docker

Pass the desired sleep time as the CMD.

$ docker run --rm -ti --name flare xr09/flare 5
Flare running with PID 1

received SIGUSR1
received SIGUSR1
received SIGUSR1
received SIGTERM
the program will take 5s to finish correctly
...
SUCCESS: the program had enough time to finish

Send USR1 with docker kill -s USR1 flare

Send TERM with docker stop flare or docker kill -s TERM flare

After receiving a SIGTERM it will print it then wait 5 seconds and shutdown.

Flare on Kubernetes

This tools is convenient for debugging cases where terminationGracePeriodSeconds is needed on Kubernetes.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: flare
  labels:
    app: flare
spec:
  replicas: 3
  selector:
    matchLabels:
      app: flare
  template:
    metadata:
      labels:
        app: flare
    spec:
      terminationGracePeriodSeconds: 60
      containers:
      - name: flare
        image: xr09/flare
        args: ["45"]

Proceed to delete one of the pods:

❯ kubectl get po
NAME                     READY   STATUS    RESTARTS   AGE
flare-777c45d94c-75lmx   1/1     Running   0          11s
flare-777c45d94c-w6kxm   1/1     Running   0          11s
flare-777c45d94c-xxsdn   1/1     Running   0          11s

❯ kubectl delete pod flare-777c45d94c-xxsdn
pod "flare-777c45d94c-xxsdn" deleted

It should have enough time to close by itself:

❯ kubectl logs -f flare-777c45d94c-xxsdn
Flare running with PID 1

received SIGTERM
the program will take 45s to finish correctly
...
SUCCESS: the program had enough time to finish