kubexit

README

kubexit

Command supervisor for coordinated process termination.

Tombstones

kubexit carves a tombstone at ${KUBEXIT_GRAVEYARD}/${KUBEXIT_NAME} to mark the birth and death of the process it supervises:

1. When a wrapped app starts, kubexit will write a tombstone with a Born timestamp.
2. When a wrapped app exits, kubexit will update the tombstone with a Died timestamp and the ExitCode.

Use Case: Romeo and Juliet

With kubexit, you can define death dependencies between processes that are wrapped with kubexit and configured with the same graveyard.

KUBEXIT_NAME=app1 \
KUBEXIT_GRAVEYARD=/graveyard \
kubexit app1 &

KUBEXIT_NAME=app2 \
KUBEXIT_GRAVEYARD=/graveyard \
KUBEXIT_DEATH_DEPS=app1
kubexit app2 &

If app1 exits before app2 does, kubexit will detect the tombstone update and send the TERM signal to app2.

Use Case: Hercules and Iphicles

With kubexit, you can define birth dependencies between processes that are wrapped with kubexit and configured with the same graveyard.

KUBEXIT_NAME=app1 \
KUBEXIT_GRAVEYARD=/graveyard \
kubexit app1 &

KUBEXIT_NAME=app2 \
KUBEXIT_GRAVEYARD=/graveyard \
KUBEXIT_BIRTH_DEPS=app1
KUBEXIT_POD_NAME=example-pod
KUBEXIT_NAMESPACE=example-namespace
kubexit app2 &

If kubexit app2 starts before app1 is ready (according to its Kubernetes readiness probe), kubexit will block the starting of app2 until app1 is ready.

Config

kubexit is configured with environment variables only, to make it easy to configure in Kubernetes and minimize entrypoint/command changes.

Tombstone:

• KUBEXIT_NAME - The name of the tombstone file to use. Must match the name of the Kubernetes pod container, if using birth dependency.
• KUBEXIT_GRAVEYARD - The file path of the graveyard directory, where tombstones will be read and written.

Death Dependency:

• KUBEXIT_DEATH_DEPS - The name(s) of this process death dependencies, comma separated.
• KUBEXIT_GRACE_PERIOD - Duration to wait for this process to exit after a graceful termination, before being killed. Default: 30s.

Birth Dependency:

• KUBEXIT_BIRTH_DEPS - The name(s) of this process birth dependencies, comma separated.
• KUBEXIT_POD_NAME - The name of the Kubernetes pod that this process and all its siblings are in.
• KUBEXIT_NAMESPACE - The name of the Kubernetes namespace that this pod is in.

Install

Build from source:

go get github.com/karlkfi/kubexit/cmd/kubexit

Copy from pre-built Alpine-based container image in a multi-stage build:

FROM karlkfi/kubexit:latest AS kubexit

FROM alpine:3.11
RUN apk --no-cache add ca-certificates tzdata
COPY --from=kubexit /bin/kubexit /bin/
ENTRYPOINT ["kubexit"]

Copy from init container to ephemeral volume:

volumes:
- name: kubexit
  emptyDir: {}

initContainers:
- name: kubexit
  image: karlkfi/kubexit:latest
  command: ['cp', '/bin/kubexit', '/kubexit/kubexit']
  volumeMounts:
  - mountPath: /kubexit
    name: kubexit

Examples

• Client Server Job
• CloudSQL Proxy Job