ExitDir is a library to signal a process should exit via the filesystem.
To use this library, on the leader process:
package main
import "chainguard.dev/exitdir"
func main() {
// Signal the other processes should exit via a new file in `EXIT_DIR`.
defer exitdir.Exit();
// ...rest of implementation.
}And then one or more follower processes:
package main
import (
"context"
"chainguard.dev/exitdir"
)
func main() {
// Decorate a context with ExitDir awareness. ExitDir will cancel the
// returned context when a new file in `EXIT_DIR` is created.
ctx := exitdir.Aware(context.Background())
// ...rest of implementation using `ctx` for lifecycle control.
}This functionally is shown locally by using a temp directory and two processes:
export EXIT_DIR=`mktemp -d`
go run ./cmd/follower &
go run ./cmd/leaderResults in:
$ export EXIT_DIR=`mktemp -d`
$ go run ./cmd/follower &
[1] 83528
$ go run ./cmd/leader
[Leader] Doing work...
[Follower] Tick 0
[Follower] Tick 1
[Follower] Tick 2
[Follower] Tick 3
[Leader] Exiting...
[Follower] Exiting...
[1]+ Done go run ./cmd/follower
$Often in Kubernetes a job with multiple containers need to solve a problem of signaling when to exit. If not coordinated, a resulting hung job looks like a failure, but in-fact was successful except one container never exited.
ko apply -f - <<EOF
apiVersion: batch/v1
kind: Job
metadata:
name: example
spec:
template:
spec:
restartPolicy: Never
containers:
- name: leader
image: ko://chainguard.dev/exitdir/cmd/leader
env:
- name: EXIT_DIR
value: "/var/exitdir"
volumeMounts:
- name: exit-dir
mountPath: "/var/exitdir"
- name: follower
image: ko://chainguard.dev/exitdir/cmd/follower
env:
- name: EXIT_DIR
value: "/var/exitdir"
volumeMounts:
- name: exit-dir
mountPath: "/var/exitdir"
volumes:
- name: exit-dir
emptyDir: {}
EOFWe can see the job finished:
% kubectl get job
NAME COMPLETIONS DURATION AGE
example 1/1 8s 17sAnd finding the pod, we can view the logs of each container:
$ kubectl logs example-78fm7 leader
[Leader] Doing work...
[Leader] Exiting...$ kubectl logs example-78fm7 follower
[Follower] Tick 0
[Follower] Tick 1
[Follower] Tick 2
[Follower] Tick 3
[Follower] Exiting...