cronetes
Cronetes is a simple daemon which creates jobs in Kubernetes at specified intervals. It is designed as a provisional solution until Kubernetes ScheduledJobs is released. For this reason it is designed to be run as a single instance. Running multiple instances (with the same configuration) will result in the same jobs being executed.
cron
By using the command cron you will launch the cron daemon. This daemon
requires a configuration file:
cronetes cron --config="config_example.yml"
It is also possible to pipe this configuration into the application using stdin:
cat config_example.yml | cronetes cron
Configuration
The configuration is a yaml file, which contains a array of jobs and their cron schedule:
# Every minute
- schedule: 0 * * * * *
job:
apiVersion: batch/v1
kind: Job
metadata:
name: sendemails
spec:
template:
metadata:
name: sendemails
spec:
restartPolicy: Never
containers:
- name: job
image: debian
The job must contain a valid Kubernetes Job.
Schedule format
Cronetes uses the cron package for scheduling. See
CRON Expression Format
for valid schedule inputs.
Docker image
There is a cronetes Docker image which you can use. It is hosted op quay.io:
quay.io/wercker/cronetes. It doesn't come with any configuration, so you need
to create a new Docker image which has the config included.
Wercker
You need to create a repository on GitHub or Bitbucket, and add this repository to wercker. Next you need the following wercker.yml:
box: debian
# build creates a config file. Currently it is a static file, but could be dynamic
build:
steps:
- termie/bash-template:
name: render config files
input: config.template.yml
- script:
name: forward config files
code: mv config.yml $WERCKER_OUTPUT_DIR
# push-quay takes cronetes as the base container, adds the config and pushes it to quay
push-quay:
box:
id: quay.io/wercker/cronetes
registry: https://quay.io
# Overriding the entrypoint: see https://github.com/wercker/wercker/issues/218
entrypoint: /bin/sh -c
cmd: /bin/sh
steps:
- script:
name: install apk packages
code: |
echo "@edge http://dl-cdn.alpinelinux.org/alpine/edge/main" >> /etc/apk/repositories
apk update && apk add ca-certificates
- script:
name: forward config files
code: mv config.yml /
- internal/docker-push:
repository: quay.io/wercker/custom-cronetes
registry: https://quay.io
username: $DOCKER_USERNAME
password: $DOCKER_PASSWORD
tag: $WERCKER_GIT_BRANCH-$WERCKER_GIT_COMMIT
entrypoint: /cronetesIn the build pipeline you need to ensure that the configuration files are
available for the next push pipeline. This can be done by simply moving
static files, using a template, or some other dynamic way.
docker build
It is also possible to create a new docker build to create a new image.
FROM quay.io/wercker/cronetes
ADD config.yml /config.yml
ENV CRONETES_CONFIG=/config.yml
Then run docker build ., and use the resulting image.
docker run
Finally it possible to pipe the config into docker when running the container:
cat config_example.yml | docker run -i quay.io/wercker/cronetes cron
Kubernetes
The easiest way to run cronetes is as a Kubernetes pod. This requires a Docker image which has the configuration included (see Docker image).
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: custom-cronetes
spec:
replicas: 1
strategy:
type: RollingUpdate
rollingUpdate:
maxUnavailable: 1
maxSurge: 0
template:
metadata:
labels:
app: custom-cronetes
spec:
containers:
- name: custom-cronetes
image: quay.io/wercker/custom-cronetes:${WERCKER_GIT_BRANCH}-${WERCKER_GIT_COMMIT}
args: [
"--kube-in-cluster",
"cron",
"--config=/config.yml",
]reap
cronetes only creates Jobs, it doesn't clean them. This binary comes with
another command called reap. This will query any Jobs that have the label
cronetes=true and will delete them.
- schedule: 0 0 * * * *
job:
apiVersion: batch/v1
kind: Job
metadata:
name: reap-jobs
spec:
template:
metadata:
name: reap-jobs
spec:
restartPolicy: Never
containers:
- name: cronetes-reap
image: quay.io/wercker/cronetes
args: [
"--kube-in-cluster",
"reap"
]
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